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Search for "free radicals" in Full Text gives 54 result(s) in Beilstein Journal of Organic Chemistry.
Advances in radical peroxidation with hydroperoxides
- Oleg V. Bityukov,
- Pavel Yu. Serdyuchenko,
- Andrey S. Kirillov,
- Gennady I. Nikishin,
- Vera A. Vil’ and
- Alexander O. Terent’ev
Beilstein J. Org. Chem. 2024, 20, 2959–3006, doi:10.3762/bjoc.20.249
- Kharasch–Sosnovsky peroxidation became the basic universal platform for the development of peroxidation methods, with its great potential for rapid generation of complexity due to the ability to couple the resulting free radicals with a wide range of partners. This review discusses the recent advances in
Graphical Abstract
Scheme 1: Organic peroxide initiators in polymer chemistry.
Scheme 2: Synthesis of organic peroxides.
Scheme 3: Richness of radical cascades with species formed from hydroperoxides in redox conditions.
Scheme 4: Co-catalyzed allylic peroxidation of alkenes 1 and 3 by TBHP.
Scheme 5: Allylic peroxidation of alkenes 6 by Pd(II)TBHP.
Scheme 6: Cu(I)-catalyzed allylic peroxidation.
Scheme 7: Enantioselective peroxidation of alkenes 10 with TBHP in the presence of copper(I) compounds.
Scheme 8: Oxidation of α-pinene (12) by the Cu(I)/TBHP system.
Scheme 9: Introduction of the tert-butylperoxy fragment into the α-position of cyclic ketones 15 and 17.
Scheme 10: α-Peroxidation of β-dicarbonyl compounds 19 using the Cu(II)/TBHP system.
Scheme 11: Co-catalyzed peroxidation of cyclic compounds 21 with TBHP.
Scheme 12: Co-, Mn- and Fe-catalyzed peroxidation of 2-oxoindoles 23, barbituric acids 25, and 4-hydroxycoumar...
Scheme 13: Cu-catalyzed and metal-free peroxidation of barbituric acid derivatives 31 and 3,4-dihydro-1,4-benz...
Scheme 14: Electrochemical peroxidation of 1,3-dicarbonyl compounds 35.
Scheme 15: Peroxidation of β-dicarbonyl compounds, cyanoacetic esters and malonic esters 37 by the TBAI/TBHP s...
Scheme 16: Cu-catalyzed peroxidation of malonodinitriles and cyanoacetic esters 39 with TBHP.
Scheme 17: Mn-catalyzed remote peroxidation via trifluromethylation of double bond.
Scheme 18: Cu-catalyzed remote peroxidation via trifluromethylthiolation of double bond.
Scheme 19: Fe-, Mn-, and Ru-catalyzed peroxidation of alkylaromatics 45, 47, 49, and 51 with TBHP.
Scheme 20: Cu-catalyzed peroxidation of diphenylacetonitrile (53) with TBHP.
Scheme 21: Cu-catalyzed peroxidation of benzyl cyanides 60 with TBHP.
Scheme 22: Synthesis of tert-butylperoxy esters 63 from benzyl alcohols 62 using the TBAI/TBHP system.
Scheme 23: Enantioselective peroxidation of 2-phenylbutane (64) with TBHP and chiral Cu(I) complex.
Scheme 24: Photochemical synthesis of peroxides 67 from carboxylic acids 66.
Scheme 25: Photochemical peroxidation of benzylic C(sp3)–H.
Scheme 26: Cu- and Ru-catalyzed peroxidation of alkylamines with TBHP.
Scheme 27: Peroxidation of amides 76 with the TBAI/TBHP system.
Scheme 28: Fe-catalyzed functionalization of ethers 78 with TBHP.
Scheme 29: Synthesis of 4-(tert-butylperoxy)-5-phenyloxazol-2(3H)-ones 82 from benzyl alcohols 80 and isocyana...
Scheme 30: Fe- and Co-catalyzed peroxidation of alkanes with TBHP.
Scheme 31: Rh-catalyzed tert-butylperoxy dienone synthesis with TBHP.
Scheme 32: Rh- and Cu-catalyzed phenolic oxidation with TBHP.
Scheme 33: Metal-free peroxidation of phenols 94.
Scheme 34: Cu-catalyzed alkylation–peroxidation of acrylonitrile.
Scheme 35: Cu-catalyzed cycloalkylation–peroxidation of coumarins 99.
Scheme 36: Metal-free cycloalkylation–peroxidation of coumarins 102.
Scheme 37: Difunctionalization of indene 104 with tert-butylperoxy and alkyl groups.
Scheme 38: Acid-catalyzed radical addition of ketones (108, 111) and TBHP to alkenes 107 and acrylates 110.
Scheme 39: Cu-catalyzed alkylation–peroxidation of alkenes 113 with TBHP and diazo compounds 114.
Scheme 40: Cobalt(II)-catalyzed addition of TBHP and 1,3-dicarbonyl compound 116 to alkenes 117.
Scheme 41: Cu(0)- or Co(II)-catalyzed addition of TBHP and alcohols 120 to alkenes 119.
Scheme 42: Fe-catalyzed functionalization of allenes 122 with TBHP.
Scheme 43: Fe-catalyzed alkylation–peroxidation of alkenes 125 and 127.
Scheme 44: Fe- and Co-catalyzed alkylation–peroxidation of alkenes 130, 133 and 134 with TBHP and aldehydes as...
Scheme 45: Carbonylation–peroxidation of alkenes 137, 140, 143 with hydroperoxides and aldehydes.
Scheme 46: Carbamoylation–peroxidation of alkenes 146 with formamides and TBHP.
Scheme 47: TBAB-catalyzed carbonylation–peroxidation of alkenes.
Scheme 48: VOCl2-catalyzed carbonylation–peroxidation of alkenes 152.
Scheme 49: Acylation–peroxidation of alkenes 155 with aldehydes 156 and TBHP using photocatalysis.
Scheme 50: Cu-catalyzed peroxidation of styrenes 158.
Scheme 51: Fe-catalyzed acylation-peroxidation of alkenes 161 with carbazates 160 and TBHP.
Scheme 52: Difunctionalization of alkenes 163, 166 with TBHP and (per)fluoroalkyl halides.
Scheme 53: Difunctionalization of alkenes 169 and 172 with hydroperoxides and sodium (per)fluoromethyl sulfina...
Scheme 54: Trifluoromethylation–peroxidation of styrenes 175 using MOF Cu3(BTC)2 as a catalyst.
Scheme 55: Difunctionalization of alkenes 178 with tert-butylperoxy and dihalomethyl fragments.
Scheme 56: Difunctionalization of alkenes 180 with the tert-butylperoxy and dihalomethyl moieties.
Scheme 57: The nitration–peroxidation of alkenes 182 with t-BuONO and TBHP.
Scheme 58: Azidation–peroxidation of alkenes 184 with TMSN3 and TBHP.
Scheme 59: Co-catalyzed bisperoxidation of butadiene 186.
Scheme 60: Bisperoxidation of styrene (189) and acrylonitrile (192) with TBHP by Minisci.
Scheme 61: Mn-catalyzed synthesis of bis(tert-butyl)peroxides 195 from styrenes 194.
Scheme 62: Bisperoxidation of arylidene-9H-fluorenes 196 and 3-arylidene-2-oxoindoles 198 with TBHP under Mn-c...
Scheme 63: Synthesis of bisperoxides from styrenes 200 and 203 using the Ru and Rh catalysis.
Scheme 64: Iodine-catalyzed bisperoxidation of styrenes 206.
Scheme 65: Synthesis of di-tert-butylperoxyoxoindoles 210 from acrylic acid anilides 209 using a Pd(II)/TBHP o...
Scheme 66: Pinolation/peroxidation of styrenes 211 catalyzed by Cu(I).
Scheme 67: TBAI-catalyzed acyloxylation–peroxidation of alkenes 214 with carboxylic acids and TBHP.
Scheme 68: Difunctionalization of alkenes 217 with TBHP and water or alcohols.
Scheme 69: TBAI-catalyzed hydroxyperoxidation of 1,3-dienes 220.
Scheme 70: Hydroxyperoxidation of 1,3-dienes 220.
Scheme 71: Iodination/peroxidation of alkenes 223 with I2 and hydroperoxides.
Scheme 72: The reactions of cyclic enol ethers 226 and 228 with I2/ROOH system.
Scheme 73: Synthesis of 1-(tert-butylperoxy)-2-iodoethanes 231.
Scheme 74: Synthesis of 1-iodo-2-(tert-butylperoxy)ethanes 233.
Scheme 75: Cu-catalyzed phosphorylation–peroxidation of alkenes 234.
Scheme 76: Co-catalyzed phosphorylation–peroxidation of alkenes 237.
Scheme 77: Ag-catalyzed sulfonylation–peroxidation of alkenes 241.
Scheme 78: Co-catalyzed sulfonylation–peroxidation of alkenes 244.
Scheme 79: Synthesis of α/β-peroxysulfides 248 and 249 from styrenes 247.
Scheme 80: Cu-catalyzed trifluoromethylthiolation–peroxidation of alkenes 250 and allenes 252.
Scheme 81: Photocatalytic sulfonyl peroxidation of alkenes 254 via deamination of N-sulfonyl ketimines 255.
Scheme 82: Photoredox-catalyzed 1,4-peroxidation–sulfonylation of enynones 257.
Scheme 83: Cu-catalyzed silylperoxidation of α,β-unsaturated compounds 260 and enynes 261.
Scheme 84: Fe-catalyzed silyl peroxidation of alkenes.
Scheme 85: Cu-catalyzed germyl peroxidation of alkenes 267.
Scheme 86: TBAI-catalyzed intramolecular cyclization of diazo compounds 269 with further peroxidation.
Scheme 87: Co-catalyzed three-component coupling of benzamides 271, diazo compounds 272 and TBHP.
Scheme 88: Co-catalyzed esterification-peroxidation of diazo compounds 274 with TBHP and carboxylic acids 275.
Scheme 89: Cu-catalyzed alkylation–peroxidation of α-carbonylimines 277 or ketones 280.
Scheme 90: Mn-catalyzed ring-opening peroxidation of cyclobutanols 282 with TBHP.
Scheme 91: Peroxycyclization of tryptamines 284 with TBHP.
Scheme 92: Radical cyclization–peroxidation of homotryptamines 287.
Scheme 93: Iodine-catalyzed oxidative coupling of indoles 288, cyanoacetic esters and TBHP.
Scheme 94: Summary of metal-catalyzed peroxidation processes.
Research progress on the pharmacological activity, biosynthetic pathways, and biosynthesis of crocins
- Zhongwei Hua,
- Nan Liu and
- Xiaohui Yan
Beilstein J. Org. Chem. 2024, 20, 741–752, doi:10.3762/bjoc.20.68
- also reported to inhibit cell invasion and metastasis [54][55]. Anti-inflammation and antioxidation Crocins exhibit anti-inflammation properties by scavenging free radicals and regulating the expression of antioxidant enzymes. Crocins can inhibit the NF-κB signaling pathway, thus downregulating the
Graphical Abstract
Figure 1: Principal structure of crocin and crocetin derivatives, including common substituents of the crocet...
Figure 2: The pharmacological activity and mechanisms of action of crocins.
Figure 3: Crocin biosynthetic pathways in C. sativus and G. jasminoides. Enzyme abbreviations are as follows:...
Mechanisms for radical reactions initiating from N-hydroxyphthalimide esters
- Carlos R. Azpilcueta-Nicolas and
- Jean-Philip Lumb
Beilstein J. Org. Chem. 2024, 20, 346–378, doi:10.3762/bjoc.20.35
- intermediacy of free radicals, indicating the involvement of the SET pathway (Scheme 21C). Eventually, reductive elimination of 113 afforded product 114 while regenerating the catalytic species 109. It is worth nothing that further transformations of NHPI esters under photoinduced Cu catalysis have been
Graphical Abstract
Scheme 1: Comparison between Barton and NHPI ester radical precursors.
Scheme 2: Overview of the mechanisms and activation modes involved in radical generation from RAEs.
Scheme 3: Common mechanisms in photocatalysis.
Scheme 4: A) Giese-type radical addition of NHPI esters mediated by a reductive quenching photocatalytic cycl...
Scheme 5: A) Minisci-type radical addition of NHPI esters. B) Reaction mechanism involving an “off-cycle” red...
Scheme 6: Activation of NHPI esters through hydrogen-bonding in an oxidative quenching photocatalytic cycle.
Scheme 7: SET activation of RAE facilitated by a Lewis acid catalyst.
Scheme 8: PCET activation of NHPI esters in the context of a radical-redox annulation.
Scheme 9: Activation enabled by a strong excited-state reductant catalyst and its application in the dearomat...
Scheme 10: Proposed formation of an intramolecular charge-transfer complex in the synthesis of (spiro)anellate...
Scheme 11: Formation of a charge-transfer complex between enamides and NHPI esters enabled by a chiral phospha...
Scheme 12: Activation of NHPI ester through the formation of photoactive EDA-complexes.
Scheme 13: A) EDA complex-mediated radical hydroalkylation reactions of NHPI esters. B) Proposed mechanism for...
Scheme 14: Proposed radical chain mechanism initiated by EDA-complex formation.
Scheme 15: A) Photoinduced decarboxylative borylation. B) Proposed radical chain mechanism.
Scheme 16: A) Activation of NHPI esters mediated by PPh3/NaI. B) Proposed catalytic cycle involving EDA-comple...
Scheme 17: A) Radical generation facilitated by EDA complex formation between PTH1 catalyst and NHPI esters. B...
Scheme 18: Proposed catalytic cycle for the difunctionalization of styrenes.
Scheme 19: Formation of a charge-transfer complex between NHPI esters and Cs2CO3 enables decarboxylative amina...
Scheme 20: 3-Acetoxyquinuclidine as catalytic donor in the activation of TCNHPI esters.
Scheme 21: A) Photoinduced Cu-catalyzed decarboxylative amination. B) Proposed catalytic cycle. C) Radical clo...
Scheme 22: A) Photoinduced Pd-catalyzed aminoalkylation of 1,4-dienes. B) Proposed catalytic cycle.
Scheme 23: A) TM-catalyzed decarboxylative coupling of NHPI esters and organometallic reagents. B) Representat...
Scheme 24: Synthetic applications of the TM-catalyzed decarboxylative coupling of NHPI esters and organometall...
Scheme 25: A) Ni-catalyzed cross-electrophile coupling of NHPI esters. B) Representative catalytic cycle.
Scheme 26: A) Synthetic applications of decarboxylative cross-electrophile couplings. B) Decarboxylative aryla...
Scheme 27: A) Activation of tetrachlorophthalimide redox-active esters enabled by a low-valency Bi complex. B)...
Scheme 28: Activation of NHPI esters mediated by Zn0 applied in a Z-selective alkenylation reaction.
Scheme 29: A) Activation of NHPI esters enabled by a pyridine-boryl radical species applied to the decarboxyla...
Scheme 30: A) Decarboxylative coupling of RAE and aldehydes enabled by NHC-catalyzed radical relay. B) Propose...
Scheme 31: A) Decarboxylative C(sp3)–heteroatom coupling reaction of NHPI esters under NHC catalysis B) The NH...
Scheme 32: A) Electrochemical Giese-type radical addition of NHPI esters. B) Reaction mechanism.
Scheme 33: Electrochemical Minisci-type radical addition of NHPI-esters.
Scheme 34: Ni-electrocatalytic cross-electrophile coupling of NHPI esters with aryl iodides.
Scheme 35: A) Decarboxylative arylation of NHPI esters under Ag-Ni electrocatalysis B) Formation of AgNP on th...
Scheme 36: Synthetic applications of decarboxylative couplings of NHPI esters under Ni-electrocatalysis.
Scheme 37: Examples of natural product syntheses in which RAEs were used in key C–C bond forming reactions.
Radical chemistry in polymer science: an overview and recent advances
- Zixiao Wang,
- Feichen Cui,
- Yang Sui and
- Jiajun Yan
Beilstein J. Org. Chem. 2023, 19, 1580–1603, doi:10.3762/bjoc.19.116
- conventional radical polymerization. Most free radicals have an extremely short lifetime due to a diffusion-controlled termination process between two free radicals. The inevitable termination between radicals makes the synthesis of well-defined polymers and co-polymers very difficult. In addition, polymers
- initiator is needed to start the radical crosslinking. Besides sulfur, peroxides such as di-tert-butylcumyl peroxide (BCUP) and dicumyl peroxide (DCP) are often used in radical crosslinking. Free radicals are generated at the peroxides’ decomposition temperature and attack the polymer chains to achieve
Graphical Abstract
Scheme 1: Oxidation of catechol and subsequent cross-linking. Scheme 1 redrawn from [3].
Scheme 2: (A) Structure of typical urushiol in Chinese lacquer, and (B) schematic process of laccase-catalyze...
Scheme 3: A) Primary amino acid sequence of mfp-1, mfp-3, and mfp-5 (Y: DOPA, K: lysine). B) Scheme showing e...
Scheme 4: Activation–deactivation equilibrium in nitroxide-mediated polymerizations. Bicomponent initiating s...
Scheme 5: Mechanism of a transition metal complex-mediated ATRP. Scheme 5 redrawn from [14].
Scheme 6: Mechanism of RAFT polymerization. Scheme 6 redrawn from [68].
Scheme 7: Degenerative transfer (a) and reversible termination (b) mechanism of OMRP. Scheme 7 redrawn from [70].
Scheme 8: Simplified mechanism of a RITP. Scheme 8 redrawn from [21].
Scheme 9: (A) Structures of π-conjugated conductive polymers. (B) Examples of conductive polymer synthesis vi...
Scheme 10: Possible regiochemical couplings in PATs. Scheme 10 redrawn from [79].
Scheme 11: General thiol-ene photopolymerization process. Scheme 11 redrawn from [81].
Scheme 12: (a) Three generations of Grubbs catalysts. (b) Proposed mechanism for photo-ROMP via a reductive qu...
Scheme 13: Pyrylium and thiopyrylium salts studied by Boydston et al. Scheme 13 redrawn from [91].
Scheme 14: A general illustration of post-polymerization modification by thiol–ene chemistry.
Scheme 15: Introduction of functionalities by nitroxide radical coupling of HO-TEMPO derivatives.
Scheme 16: Chemical reaction process scheme of DCP-induced crosslinking of LDPE. Scheme 16 redrawn from [126].
Scheme 17: A probable mechanism of radical-induced hydrosilylation.
Scheme 18: Polymer surface modification by homolytic dediazonation of diazonium salts.
Scheme 19: Photoinduced polymer surface modification or surface grafting using benzophenone.
Scheme 20: Depolymerization mechanism of common photoresists. (a) A possible mechanism of radiation decomposit...
Scheme 21: Proposed mechanisms of photooxidative depolymerization of polystyrene. (a) Scheme 21a was reprinted with perm...
Synthesis of 5-arylidenerhodanines in L-proline-based deep eutectic solvent
- Stéphanie Hesse
Beilstein J. Org. Chem. 2023, 19, 1537–1544, doi:10.3762/bjoc.19.110
- recycled for several runs [20]. As some benzylidenerhodanine derivatives were already reported for their antioxidant activities [3], we investigated those compounds for their antioxidant activity expressed as percentage of 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) scavenging activity. DPPH free radicals
Graphical Abstract
Figure 1: Examples of rhodanines and related five-membered heterocycles with interesting biological activitie...
Scheme 1: Synthesis of 5-benzylidenerhodanine derivatives. Conditions: areaction performed for 3 h at 60 °C. b...
Photoredox catalysis harvesting multiple photon or electrochemical energies
- Mattia Lepori,
- Simon Schmid and
- Joshua P. Barham
Beilstein J. Org. Chem. 2023, 19, 1055–1145, doi:10.3762/bjoc.19.81
- formation which corroborates the involvement of free radicals. The authors argued against radical chain propagation on the basis of lack of reactivity in the dark during the light ON-OFF cycle experiments (we note that this does not rule out chain propagation with an efficient chain death). Investigations
- the most appropriate for a given reaction, scale and purpose of a project. Keywords: consecutive photoinduced electron transfer; electro-activated photoredox catalysis; photoelectrochemistry; photoredox catalysis; radical ions; Review 1 Introduction Owing to the unique reactivity patterns of free
- radicals that often provide access to new dimensions of synthetic chemical space, the field of single electron transfer (SET) in organic synthesis has expanded considerably in the past two decades. Among this area, photoredox catalysis (PRC) is highly attractive due to its abilities i) to generate reactive
Graphical Abstract
Figure 1: Oxidative and reductive activations of organic compounds harvesting photoredox catalysis.
Figure 2: General catalytic cycles of radical ion conPET (left) and radical ion e-PRC (right).
Figure 3: “Beginner’s guide”: comparison between advantages, capacities, and prospectives of conPET and PEC.
Figure 4: A) conPET reductive dehalogenation of aryl halides with PDI. B) Reductive C–H arylation with pyrrol...
Figure 5: A) Chromoselective mono- and disubstitution or polybrominated pyrimidines with pyrroles. B) Sequent...
Figure 6: A) Synthesis of pyrrolo[1,2-a]quinolines. B) Synthesis of ullazines.
Figure 7: A) Reductive phosphorylation of aryl halides via conPET. B) Selected examples from the substrate sc...
Figure 8: A) Reductive dehalogenation of aryl halides via conPET and selected examples from the substrate sco...
Figure 9: A) Reductive C–H arylation of aryl halides via conPET (top) and selected examples from the substrat...
Figure 10: A) Reductive hydrodehalogenation of aryl halides with Mes-Acr-BF4. B) Selected examples from the su...
Figure 11: A) Reductive hydrodechlorination of aryl chlorides with 4-DPAIPN. B) Proposed formation of CO2•−. C...
Figure 12: A) Reductive conPET borylation with 3CzEPAIPN (top) and selected examples from the substrate scope ...
Figure 13: Scale-up of conPET phosphorylation with 3CzEPAIPN.
Figure 14: A) Borylation of 1d. B) Characteristics and structure of PC1 with green and red parts showing the l...
Figure 15: A) Reductive C–H arylation scope with polysulfide conPET (top) and selected examples from the subst...
Figure 16: Scale-up of A) C–H arylation and B) dehaloborylation with polysulfide photocatalysis in continuous-...
Figure 17: A) Formation of [Ir1]0 and [Ir2]0 upon PET between [Ir1]+ and Et3N. B) Mechanism of multi-photon ta...
Figure 18: A) Reductive hydrodehalogenation of aryl halides via multi-photon tandem photocatalysis. B) Selecte...
Figure 19: A) Carbonylative amidation of aryl halides in continuous flow. B) Selected examples from the substr...
Figure 20: A) General scheme for reductive (RQ) and oxidative quenching (OQ) protocols using [FeIII(btz)3](PF6)...
Figure 21: A) Carbonylative amidation of alkyl iodides with [IrIII(ppy)2(dtbbpy)]PF6. B) Selected examples fro...
Figure 22: A) Carboxylative C–N bond cleavage in cyclic amines. B) Selected examples from the substrate scope....
Figure 23: A) Formal reduction of alkenes to alkanes via transfer hydrogenation. B) Selected examples from the...
Figure 24: A) Birch-type reduction of benzenes with PMP-BPI. B) Selected examples from the substrate scope (sc...
Figure 25: Proposed mechanism of the OH− mediated conPET Birch-type reduction of benzene via generation of sol...
Figure 26: Reductive detosylation of N-tosylated amides with Mes-Acr-BF4. B) Selected examples from the substr...
Figure 27: A) Reductive detosylation of N-tosyl amides by dual PRC. B) Selected examples from the substrate sc...
Figure 28: A) Mechanism of the dual PRC based on PET between [Cu(dap)2]+ and DCA. B) Mechanism of the dual PRC...
Figure 29: A) N–O bond cleavage in Weinreb amides with anthracene. B) N–O bond cleavage in Weinreb amides rely...
Figure 30: A) Pentafluorosulfanylation and fluoride elimination. B) Mechanism of the pentafluorosulfanylation ...
Figure 31: A) α-Alkoxypentafluorosulfanylation (top) and selected examples from the substrate scope (bottom). ...
Figure 32: A) Oxidative amination of arenes with azoles catalyzed by N-Ph PTZ. B) Selected examples from the s...
Figure 33: A) C(sp3)–H bond activation by HAT via chloride oxidation by *N-Ph PTZ•+. B) Proposed mechanism for...
Figure 34: A) Recycling e-PRC C–H azolation of electron-rich arenes with pyrazoles using Mes-Acr+ as a photoca...
Figure 35: A) Radical ion e-PRC direct oxidation of unactivated arenes using TAC+ as an electro-activated phot...
Figure 36: A) Radical ion e-PRC direct oxidation of unactivated arenes using TPA as an electro-activated photo...
Figure 37: Proposed mechanism (top) and mode of preassembly (bottom).
Figure 38: A) Possible preassemblies of reactive (left) vs unreactive (right) arenes. B) Calculated spin densi...
Figure 39: A) Recycling e-PRC C(sp2 )–H acetoxylation of arenes using DDQ as a photocatalyst. B) Proposed cata...
Figure 40: Gram scale hydroxylation of benzene in a recirculated flow setup.
Figure 41: A) Radical ion e-PRC vicinal diamination of alkylarenes using TAC+ as an electro-activated photocat...
Figure 42: A) Sequential oxygenation of multiple adjacent C–H bonds under radical ion e-PRC using TAC+ as an e...
Figure 43: A) Enantioselective recycling e-PRC cyanation of benzylic C–H bonds using ADQS as photocatalyst. B)...
Figure 44: Proposed tandem mechanism by Xu and co-workers.
Figure 45: A) Enantioselective recycling e-PRC decarboxylative cyanation using Cu(acac)2, Ce(OTf)3 and a box l...
Figure 46: A) Enantioselective recycling e-PRC benzylic cyanation using Cu(MeCN)4BF4, box ligand and anthraqui...
Figure 47: A) Radical ion e-PRC acetoxyhydroxylation of aryl olefins using TAC+ as an electro-activated photoc...
Figure 48: Selected examples from the substrate scope.
Figure 49: Photoelectrochemical acetoxyhydroxylation in a recirculated flow setup.
Figure 50: A) Radical ion e-PRC aminooxygenation of aryl olefins using TAC+ as an electro-activated photocatal...
Figure 51: A) Recycling e-PRC C–H alkylation of heteroarenes with organic trifluoroborates using Mes-Acr+ as p...
Figure 52: A) Recycling e-PRC decarboxylative C–H alkylation of heteroarenes using CeCl3·7H2O as catalyst. B) ...
Figure 53: A) Recycling e-PRC decarboxylative C–H alkylation of heteroarenes using Fe(NH4)2(SO4)2·6H2O as cata...
Figure 54: A) Recycling e-PRC C–H alkylation of heteroarenes with alkyl oxalates and 4CzIPN as photocatalyst. ...
Figure 55: A) Recycling e-PRC decarboxylative C–H carbamoylation of heteroarenes using 4CzIPN as photocatalyst...
Figure 56: A) Photoelectrochemical HAT-mediated hydrocarbon activation via the chlorine radical. B) Proposed m...
Figure 57: A) Selected examples from the substrate scope. B) Gram and decagram scale semi-continuous flow PEC ...
Figure 58: A) Photoelectrochemical HAT-mediated dehydrogenative coupling of benzothiazoles with aliphatic C–H ...
Figure 59: A) Photoelectrochemical HAT activation of ethers using electro-activated TAC+ as photocatalyst. B) ...
Figure 60: Selected examples from the substrate scope.
Figure 61: A) Photoelectrochemical HAT-mediated synthesis of alkylated benzimidazo-fused isoquinolinones using...
Figure 62: A) Decoupled photoelectrochemical cerium-catalyzed oxydichlorination of alkynes using CeCl3 as cata...
Figure 63: Proposed decoupled photoelectrochemical mechanism.
Figure 64: A) Decoupled photoelectrochemical ring-opening bromination of tertiary cycloalkanols using MgBr2 as...
Figure 65: A) Recycling e-PRC ring-opening functionalization of cycloalkanols using CeCl3 as catalyst. B) Prop...
Figure 66: Selected examples from the substrate scope of the PEC ring-opening functionalization.
Figure 67: A) Radical ion e-PRC reduction of chloro- and bromoarenes using DCA as catalyst and various accepto...
Figure 68: A) Screening of different phthalimide derivatives as catalyst for the e-PRC reduction of aryl halid...
Figure 69: Screening of different organic catalysts for the e-PRC reduction of trialkylanilium salts.
Figure 70: A) e-PRC reduction of phosphonated phenols and anilinium salts. B) Selected examples from the subst...
Figure 71: A) ConPET and e-PRC reduction of 4-bromobenzonitrile using a naphthalene diimide (NDI) precatalyst ...
Figure 72: A) Radical ion e-PRC reduction of phosphinated aliphatic alcohols with n-BuO-NpMI as catalyst. B) C...
Figure 73: Selected examples from the substrate scope.
Figure 74: A) Recycling e-PRC reductive dimerization of benzylic chlorides using a [Cu2] catalyst. B) Proposed...
Figure 75: A) Decoupled photoelectrochemical C–H alkylation of heteroarenes through deamination of Katritzky s...
Figure 76: Proposed mechanism by Chen and co-workers.
Redox-active molecules as organocatalysts for selective oxidative transformations – an unperceived organocatalysis field
- Elena R. Lopat’eva,
- Igor B. Krylov,
- Dmitry A. Lapshin and
- Alexander O. Terent’ev
Beilstein J. Org. Chem. 2022, 18, 1672–1695, doi:10.3762/bjoc.18.179
- /peroxide, quinones, and iodine(I/III) compounds are the most developed catalyst types which are covered here. Keywords: CH-functionalization; free radicals; hypervalent iodine; N-oxyl radicals; redox-active molecules; Introduction Organocatalysis can be defined as catalysis by small organic molecules
Graphical Abstract
Scheme 1: Organocatalysis classification used in the present perspective.
Scheme 2: Oxidative processes catalyzed by amines.
Scheme 3: N-Heterocyclic carbene (NHC) catalysis in oxidative functionalization of aldehydes.
Scheme 4: Examples of asymmetric oxidative processes catalyzed by chiral Brønsted acids.
Scheme 5: Asymmetric aerobic α-hydroxylation of lactams under phase-transfer organocatalysis conditions emplo...
Scheme 6: Selective CH-oxidation of methylarenes to aldehydes or carboxylic acids.
Scheme 7: An example of the regioselective CH-amination by a sterically hindered imide-N-oxyl radical precurs...
Scheme 8: CH-amination of ethylbenzene and CH-fluorination of aldehydes catalyzed by N-hydroxybenzimidazoles,...
Scheme 9: Mixed hetero-/homogeneous TiO2/N-hydroxyimide photocatalysis in the selective benzylic oxidation.
Scheme 10: Electrochemical benzylic iodination and benzylation of pyridine by benzyl iodides generated in situ...
Scheme 11: Electrochemical oxidative C–O/C–N coupling of alkylarenes with NHPI. Electrolysis conditions: Const...
Scheme 12: Chemoselective alcohol oxidation catalyzed by TEMPO.
Scheme 13: ABNO-catalyzed oxidative C–N coupling of primary alcohols with primary amines.
Scheme 14: ACT-catalyzed electrochemical oxidation of primary alcohols and aldehydes to carboxylic acids.
Scheme 15: Electrocatalytic oxidation of benzylic alcohols by a TEMPO derivative immobilized on a graphite ano...
Scheme 16: Electrochemical oxidation of carbamates of cyclic amines to lactams and oxidative cyanation of amin...
Scheme 17: Hydrogen atom transfer (HAT) and single-electron transfer (SET) as basic principles of amine cation...
Scheme 18: Electrochemical quinuclidine-catalyzed oxidation involving unactivated C–H bonds.
Scheme 19: DABCO-mediated photocatalytic C–C cross-coupling involving aldehyde C–H bond cleavage.
Scheme 20: DABCO-derived cationic catalysts in inactivated C–H bond cleavage for alkyl radical addition to ele...
Scheme 21: Electrochemical diamination and dioxygenation of vinylarenes catalyzed by triarylamines.
Scheme 22: Electrochemical benzylic oxidation mediated by triarylimidazoles.
Scheme 23: Thiyl radical-catalyzed CH-arylation of allylic substrates by aryl cyanides.
Scheme 24: Synthesis of redox-active alkyl tetrafluoropyridinyl sulfides by unactivated C–H bond cleavage by t...
Scheme 25: Main intermediates in quinone oxidative organocatalysis.
Scheme 26: Electrochemical DDQ-catalyzed intramolecular dehydrogenative aryl–aryl coupling.
Scheme 27: DDQ-mediated cross-dehydrogenative C–N coupling of benzylic substrates with azoles.
Scheme 28: Biomimetic o-quinone-catalyzed benzylic alcohol oxidation.
Scheme 29: Electrochemical synthesis of secondary amines by oxidative coupling of primary amines and benzylic ...
Scheme 30: General scheme of dioxirane and oxaziridine oxidative organocatalysis.
Scheme 31: Dioxirane organocatalyzed CH-hydroxylation involving aliphatic C(sp3)–H bonds.
Scheme 32: Enantioselective hydroxylation of CH-acids catalyzed by chiral oxaziridines.
Scheme 33: Iodoarene-organocatalyzed vinylarene diamination.
Scheme 34: Iodoarene-organocatalyzed asymmetric CH-hydroxylation of benzylic substrates.
Scheme 35: Iodoarene-organocatalyzed asymmetric difluorination of alkenes with migration of aryl or methyl gro...
Scheme 36: Examples of 1,2-diiodo-4,5-dimethoxybenzene-catalyzed electrochemical oxidative heterocyclizations.
Scheme 37: Electrochemical N-ammonium ylide-catalyzed CH-oxidation.
Scheme 38: Oxidative dimerization of aryl- and alkenylmagnesium compounds catalyzed by quinonediimines.
Scheme 39: FLP-catalyzed dehydrogenation of N-substituted indolines.
Structural basis for endoperoxide-forming oxygenases
- Takahiro Mori and
- Ikuro Abe
Beilstein J. Org. Chem. 2022, 18, 707–721, doi:10.3762/bjoc.18.71
- , natural and (semi)synthetic endoperoxides with wide structural diversity show antimalarial activity against Plasmodium falciparum malaria. In this case, the reductive activation of the endoperoxide ring with the homolytic cleavage of the O–O bond leads to the generation of carbon-centered free radicals
Graphical Abstract
Figure 1: Examples of endoperoxide-containing natural products.
Scheme 1: Reactions of COXs.
Figure 2: Structures of COXs [52,53]. (A) The overall structure of ovine COX-1. (B and C) Comparison of the cyclooxy...
Scheme 2: Proposed reaction mechanisms of COXs [24].
Scheme 3: General reaction mechanism of Fe/2OG oxygenases.
Scheme 4: Reaction of FtmOx1 [68-71].
Figure 3: Structure of FtmOx1 [71]. (A) The FtmOx1 binary structure in complex with 2OG. (B and C) Comparison of ...
Scheme 5: Proposed COX-like mechanism of FtmOx1 [68].
Scheme 6: Proposed CarC-like mechanism of FtmOx1 [70].
Scheme 7: Reaction of NvfI [28].
Scheme 8: Possible reaction pathways leading to fumigatonoid A [28].
Figure 4: Structure of NvfI [28]. (A–C) Conformational changes of loop regions: (A) open conformation, (B) partia...
Scheme 9: Another possible reaction pathway for the formation of fumigatonoid A [28].
Menadione: a platform and a target to valuable compounds synthesis
- Acácio S. de Souza,
- Ruan Carlos B. Ribeiro,
- Dora C. S. Costa,
- Fernanda P. Pauli,
- David R. Pinho,
- Matheus G. de Moraes,
- Fernando de C. da Silva,
- Luana da S. M. Forezi and
- Vitor F. Ferreira
Beilstein J. Org. Chem. 2022, 18, 381–419, doi:10.3762/bjoc.18.43
- useful alkylation approach is the Kochi–Anderson method [76] (or also known as Jacobsen–Torssell method [77][78]), via oxidative decarboxylation, where the quinone reacts with a carboxylic acid in the presence of silver(I) nitrate and ammonium or potassium peroxydisulfate. Nucleophilic free radicals are
- 24–75% yields (Scheme 28). Alkylation and acylation by free radicals One of the largest groups of reactions that use menadione (10) as substrate comprises free radical alkylation and acylation reactions. The most useful alkylation approach is the Kochi–Anderson method [76] or (Jacobsen–Torssell
Graphical Abstract
Figure 1: Natural bioactive naphthoquinones.
Figure 2: Chemical structures of vitamins K.
Figure 3: Redox cycle of menadione.
Scheme 1: Selected approaches for menadione synthesis using silver(I) as a catalyst.
Scheme 2: Methylation approaches for the preparation of menadione from 1,4-naphthoquinone using tert-butyl hy...
Scheme 3: Methylation approach of 1,4-naphthoquinone using i) rhodium complexes/methylboronic acid and ii) bi...
Scheme 4: Synthesis of menadione (10) from itaconic acid.
Scheme 5: Menadione synthesis via Diels–Alder reaction.
Scheme 6: Synthesis of menadione (10) using p-cresol as a synthetic precursor.
Scheme 7: Synthesis of menadione (10) via demethoxycarbonylating annulation of methyl methacrylate.
Scheme 8: Furan 34 used as a diene in a Diels–Alder reaction for the synthesis of menadione (10).
Scheme 9: o-Toluidine as a dienophile in a Diels–Alder reaction for the synthesis of menadione (10).
Scheme 10: Representation of electrochemical synthesis of menadione.
Figure 4: Reaction sites and reaction types of menadione as substrate.
Scheme 11: DBU-catalyzed epoxidation of menadione (10).
Scheme 12: Phase-transfer catalysis for the epoxidation of menadione.
Scheme 13: Menadione epoxidation using a hydroperoxide derived from (+)-norcamphor.
Scheme 14: Enantioselective Diels–Alder reaction for the synthesis of asymmetric quinone 50 catalyzed by a chi...
Scheme 15: Optimized reaction conditions for the synthesis of anthra[9,1-bc]pyranone.
Scheme 16: Synthesis of anthra[9,1-bc]furanone, anthra[9,1-bc]pyridine, and anthra[9,1-bc]pyrrole derivatives.
Scheme 17: Synthesis of derivatives employing protected trienes.
Scheme 18: Synthesis of cyclobutene derivatives of menadione.
Scheme 19: Menadione reduction reactions using sodium hydrosulfite.
Scheme 20: Green methodology for menadiol synthesis and pegylation.
Scheme 21: Menadione reduction by 5,6-O-isopropylidene-ʟ-ascorbic acid under UV light irradiation.
Scheme 22: Selected approaches of menadione hydroacetylation to diacetylated menadiol.
Scheme 23: Thiele–Winter reaction catalyzed by Bi(OTf)3.
Scheme 24: Carbonyl condensation of menadione using resorcinol and a hydrazone derivative.
Scheme 25: Condensation reaction of menadione with thiosemicarbazide.
Scheme 26: Condensation reaction of menadione with acylhydrazides.
Scheme 27: Menadione derivatives functionalized with organochalcogens.
Scheme 28: Synthesis of selenium-menadione conjugates derived from chloromethylated menadione 84.
Scheme 29: Menadione alkylation by the Kochi–Anderson method.
Scheme 30: Menadione alkylation by diacids.
Scheme 31: Menadione alkylation by heterocycles-substituted carboxylic acids.
Scheme 32: Menadione alkylation by bromoalkyl-substituted carboxylic acids.
Scheme 33: Menadione alkylation by complex carboxylic acids.
Scheme 34: Kochi–Anderson method variations for the menadione alkylation via oxidative decarboxylation of carb...
Scheme 35: Copper-catalyzed menadione alkylation via free radicals.
Scheme 36: Nickel-catalyzed menadione cyanoalkylation.
Scheme 37: Iron-catalyzed alkylation of menadione.
Scheme 38: Selected approaches to menadione alkylation.
Scheme 39: Menadione acylation by photo-Friedel–Crafts acylation reported by Waske and co-workers.
Scheme 40: Menadione acylation by Westwood procedure.
Scheme 41: Synthesis of 3-benzoylmenadione via metal-free TBAI/TBHP system.
Scheme 42: Michael-type addition of amines to menadione reported by Kallmayer.
Scheme 43: Synthesis of amino-menadione derivatives using polyalkylamines.
Scheme 44: Selected examples for the synthesis of different amino-substituted menadione derivatives.
Scheme 45: Selected examples of Michael-type addition of complex amines to menadione (10).
Scheme 46: Addition of different natural α-amino acids to menadione.
Scheme 47: Michael-type addition of amines to menadione using silica-supported perchloric acid.
Scheme 48: Indolylnaphthoquinone or indolylnaphthalene-1,4-diol synthesis reported by Yadav et al.
Scheme 49: Indolylnaphthoquinone synthesis reported by Tanoue and co-workers.
Scheme 50: Indolylnaphthoquinone synthesis from menadione by Escobeto-González and co-workers.
Scheme 51: Synthesis of menadione analogues functionalized with thiols.
Scheme 52: Synthesis of menadione-derived symmetrical derivatives through reaction with dithiols.
Scheme 53: Mercaptoalkyl acids as nucleophiles in Michael-type addition reaction to menadione.
Scheme 54: Reactions of menadione (10) with cysteine derivatives for the synthesis of quinoproteins.
Scheme 55: Synthesis of menadione-glutathione conjugate 152 by Michael-type addition.
1,2-Naphthoquinone-4-sulfonic acid salts in organic synthesis
- Ruan Carlos B. Ribeiro,
- Patricia G. Ferreira,
- Amanda de A. Borges,
- Luana da S. M. Forezi,
- Fernando de Carvalho da Silva and
- Vitor F. Ferreira
Beilstein J. Org. Chem. 2022, 18, 53–69, doi:10.3762/bjoc.18.5
- electrons through a redox cycle promoted by the 1,2- or 1,4-naphthoquinone system. In this cycle, transient reactive oxygen (ROS) and nitrogen (RNS) species are formed as free radicals, peroxides, superoxide anions, radical anions, or dianions. These species generated inside cells accelerate hypoxia and
Graphical Abstract
Figure 1: Naphthoquinones are commonly used in organic synthesis.
Figure 2: Some important natural and synthetic naphthoquinones.
Scheme 1: Synthetic studies of BNQs and reactions with amines.
Scheme 2: Methods described for the synthesis of β-NQS.
Figure 3: Drugs detected using β-NQSNa.
Scheme 3: Reactions between β-NQS and amines.
Scheme 4: Isomerization of 4-arylamino-1,2-naphthoquinones.
Scheme 5: Synthesis of unsymmetrical 2-amino-4-imino compounds.
Scheme 6: Synthesis of bis(isoxazolyl)naphthoquinones from β-NQS.
Scheme 7: The reaction of β-NQS with 30 followed by cycle condensation.
Scheme 8: Synthesis of 4-(2-amino-5-selenothiazoles)-1,2-naphthoquinones.
Scheme 9: Synthesis of amino- and phenoxy-1,2-naphthoquinones.
Scheme 10: Synthesis of 4-semicarbazide-1,2-naphthoquinone.
Scheme 11: Reactions of 4-azido-1,2-naphthoquinone.
Figure 4: Modifications that can be easily carried out from the products of β-NQS 8.
Scheme 12: Derivatives of 1,2-naphthoquinones obtained from β-NQS.
Scheme 13: Oximes as well as 4-amino- and 4-phenoxy-1,2-naphthoquinone as potential anti-inflammatory agents.
Scheme 14: Synthesis of triazoles from β-NQS.
Scheme 15: Synthesis of naphtho[1,2-d]oxazoles from β-NQS.
Scheme 16: A) Arylation and vinylation of β-NQS catalyzed by Ni(II) salts. B) Transformation of the 1,2-dicarb...
Scheme 17: Benzo[a]carbazole and benzo[c]carbazoles fused with 1,2-naphthoquinone.
Scheme 18: Synthesis of 1,2-naphthoquinones having a C=C bond from β-NQS. Method A: NaOH, EtOH/H2O, 40 °C, 2 h...
Scheme 19: C=C bond formation from β-NQS and substituted acetonitriles.
Iron-catalyzed domino coupling reactions of π-systems
- Austin Pounder and
- William Tam
Beilstein J. Org. Chem. 2021, 17, 2848–2893, doi:10.3762/bjoc.17.196
- rate-determining step of this transformation, as well as free radicals being involved in the reaction mechanism. In 2017, Luo and Li described a three-component Ag-mediated Fe-catalyzed 1,2-carboamination of alkenes 82 using alkyl nitriles 76 and amines 105 for the synthesis of γ-amino alkyl nitriles
Graphical Abstract
Figure 1: Price comparison among iron and other transition metals used in catalysis.
Scheme 1: Typical modes of C–C bond formation.
Scheme 2: The components of an iron-catalyzed domino reaction.
Scheme 3: Iron-catalyzed tandem cyclization and cross-coupling reactions of iodoalkanes 1 with aryl Grignard ...
Scheme 4: Three component iron-catalyzed dicarbofunctionalization of vinyl cyclopropanes 14.
Scheme 5: Three-component iron-catalyzed dicarbofunctionalization of alkenes 21.
Scheme 6: Double carbomagnesiation of internal alkynes 31 with alkyl Grignard reagents 32.
Scheme 7: Iron-catalyzed cycloisomerization/cross-coupling of enyne derivatives 35 with alkyl Grignard reagen...
Scheme 8: Iron-catalyzed spirocyclization/cross-coupling cascade.
Scheme 9: Iron-catalyzed alkenylboration of alkenes 50.
Scheme 10: N-Alkyl–N-aryl acrylamide 60 CDC cyclization with C(sp3)–H bonds adjacent to a heteroatom.
Scheme 11: 1,2-Carboacylation of activated alkenes 60 with aldehydes 65 and alcohols 67.
Scheme 12: Iron-catalyzed dicarbonylation of activated alkenes 68 with alcohols 67.
Scheme 13: Iron-catalyzed cyanoalkylation/radical dearomatization of acrylamides 75.
Scheme 14: Synergistic photoredox/iron-catalyzed 1,2-dialkylation of alkenes 82 with common alkanes 83 and 1,3...
Scheme 15: Iron-catalyzed oxidative coupling/cyclization of phenol derivatives 86 and alkenes 87.
Scheme 16: Iron-catalyzed carbosulfonylation of activated alkenes 60.
Scheme 17: Iron-catalyzed oxidative spirocyclization of N-arylpropiolamides 91 with silanes 92 and tert-butyl ...
Scheme 18: Iron-catalyzed free radical cascade difunctionalization of unsaturated benzamides 94 with silanes 92...
Scheme 19: Iron-catalyzed cyclization of olefinic dicarbonyl compounds 97 and 100 with C(sp3)–H bonds.
Scheme 20: Radical difunctionalization of o-vinylanilides 102 with ketones and esters 103.
Scheme 21: Dehydrogenative 1,2-carboamination of alkenes 82 with alkyl nitriles 76 and amines 105.
Scheme 22: Iron-catalyzed intermolecular 1,2-difunctionalization of conjugated alkenes 107 with silanes 92 and...
Scheme 23: Four-component radical difunctionalization of chemically distinct alkenes 114/115 with aldehydes 65...
Scheme 24: Iron-catalyzed carbocarbonylation of activated alkenes 60 with carbazates 117.
Scheme 25: Iron-catalyzed radical 6-endo cyclization of dienes 119 with carbazates 117.
Scheme 26: Iron-catalyzed decarboxylative synthesis of functionalized oxindoles 130 with tert-butyl peresters ...
Scheme 27: Iron‑catalyzed decarboxylative alkylation/cyclization of cinnamamides 131/134.
Scheme 28: Iron-catalyzed carbochloromethylation of activated alkenes 60.
Scheme 29: Iron-catalyzed trifluoromethylation of dienes 142.
Scheme 30: Iron-catalyzed, silver-mediated arylalkylation of conjugated alkenes 115.
Scheme 31: Iron-catalyzed three-component carboazidation of conjugated alkenes 115 with alkanes 101/139b and t...
Scheme 32: Iron-catalyzed carboazidation of alkenes 82 and alkynes 160 with iodoalkanes 20 and trimethylsilyl ...
Scheme 33: Iron-catalyzed asymmetric carboazidation of styrene derivatives 115.
Scheme 34: Iron-catalyzed carboamination of conjugated alkenes 115 with alkyl diacyl peroxides 163 and acetoni...
Scheme 35: Iron-catalyzed carboamination using oxime esters 165 and arenes 166.
Scheme 36: Iron-catalyzed iminyl radical-triggered [5 + 2] and [5 + 1] annulation reactions with oxime esters ...
Scheme 37: Iron-catalyzed decarboxylative alkyl etherification of alkenes 108 with alcohols 67 and aliphatic a...
Scheme 38: Iron-catalyzed inter-/intramolecular alkylative cyclization of carboxylic acid and alcohol-tethered...
Scheme 39: Iron-catalyzed intermolecular trifluoromethyl-acyloxylation of styrene derivatives 115.
Scheme 40: Iron-catalyzed carboiodination of terminal alkenes and alkynes 180.
Scheme 41: Copper/iron-cocatalyzed cascade perfluoroalkylation/cyclization of 1,6-enynes 183/185.
Scheme 42: Iron-catalyzed stereoselective carbosilylation of internal alkynes 187.
Scheme 43: Synergistic photoredox/iron catalyzed difluoroalkylation–thiolation of alkenes 82.
Scheme 44: Iron-catalyzed three-component aminoazidation of alkenes 82.
Scheme 45: Iron-catalyzed intra-/intermolecular aminoazidation of alkenes 194.
Scheme 46: Stereoselective iron-catalyzed oxyazidation of enamides 196 using hypervalent iodine reagents 197.
Scheme 47: Iron-catalyzed aminooxygenation for the synthesis of unprotected amino alcohols 200.
Scheme 48: Iron-catalyzed intramolecular aminofluorination of alkenes 209.
Scheme 49: Iron-catalyzed intramolecular aminochlorination and aminobromination of alkenes 209.
Scheme 50: Iron-catalyzed intermolecular aminofluorination of alkenes 82.
Scheme 51: Iron-catalyzed aminochlorination of alkenes 82.
Scheme 52: Iron-catalyzed phosphinoylazidation of alkenes 108.
Scheme 53: Synergistic photoredox/iron-catalyzed three-component aminoselenation of trisubstituted alkenes 82.
Towards new NIR dyes for free radical photopolymerization processes
- Haifaa Mokbel,
- Guillaume Noirbent,
- Didier Gigmes,
- Frédéric Dumur and
- Jacques Lalevée
Beilstein J. Org. Chem. 2021, 17, 2067–2076, doi:10.3762/bjoc.17.133
- as an electron-donating component with the radical cation dye•+ and therefore, the dye/borate system is able to generate additional free radicals in the reaction medium, improving, in turn, the polymerization process (Scheme 7). This behavior has already been reported in the literature and is in full
- process is expected with different NIR dyes [9]. Table 1 and Figure S2 (Supporting Information File 1) clearly show the exothermicity observed upon irradiation. The proposed NIR dye/iodonium combinations are able to generate free radicals and cationic species (Scheme 7 and Figure 4), and these two
Graphical Abstract
Scheme 1: Investigated NIR dyes.
Scheme 2: Other used chemicals.
Scheme 3: Synthetic routes to compounds Ca, Cb, and CNa.
Scheme 4: Synthetic routes to CI1, CI3, CI4, and CI6–CI9.
Scheme 5: The metathesis reaction enabling the formation of “soft” salts CBPh1-CBPh4.
Figure 1: Visible–NIR spectra of NIR dyes in ACN. A) (1) CBPh1, (2) CBPh2, (3) CBPh3, (4) CBPh4, (5) Ca, (6) ...
Figure 2: Photopolymerization profiles of PETIA monomer under air (acrylate functions conversion vs irradiati...
Figure 3: Photopolymerization profiles of PETIA monomer under air (acrylate functions conversion vs irradiati...
Scheme 6: Pictures of polymers obtained for a thickness of 1.4 mm, using a NIR dye/iod/amine 0.1:3:2, %w/w/w ...
Scheme 7: Proposed mechanism for the photochemical reactivity of NIR dyes in a three-component PIS.
Figure 4: A) Photopolymerization profiles of PETIA/epoxy blend 1:1, w/w under air (acrylate and epoxy functio...
Methodologies for the synthesis of quaternary carbon centers via hydroalkylation of unactivated olefins: twenty years of advances
- Thiago S. Silva and
- Fernando Coelho
Beilstein J. Org. Chem. 2021, 17, 1565–1590, doi:10.3762/bjoc.17.112
- (Scheme 17B). The proposed mechanism involves the formation of a cobalt hydride species that, upon transfer of a hydrogen atom to 32, generates a geminate radical pair containing a Co(II) species and a benzylic radical. The escape from the radical cage then generates the corresponding free radicals, which
- on the solvent radical cage efficiency and, consequently, on the concentration and “life-time” of the alkyl free radicals generated after the solvent cage collapse. In the latter case, the alkyl radical needed more time to cyclize before engaging in another solvent cage. After a β–H abstraction, it
- then furnished the cycloisomerized product (Scheme 18). Carbon-centered radical additions via metal hydride hydrogen H atom transfer Tertiary carbon free radicals are useful intermediates in the construction of new all-carbon quaternary centers. The late stage transition state associated with the
Graphical Abstract
Figure 1: Some examples of natural products and drugs containing quaternary carbon centers.
Scheme 1: Simplified mechanism for olefin hydrofunctionalization using an electrophilic transition metal as a...
Scheme 2: Selected examples of quaternary carbon centers formed by the intramolecular hydroalkylation of β-di...
Scheme 3: Control experiments and the proposed mechanism for the Pd(II)-catalyzed intermolecular hydroalkylat...
Scheme 4: Intermolecular olefin hydroalkylation of less reactive ketones under Pd(II) catalysis using HCl as ...
Scheme 5: A) Selected examples of Pd(II)-mediated quaternary carbon center synthesis by intermolecular hydroa...
Scheme 6: Selected examples of quaternary carbon center synthesis by gold(III) catalysis. This is the first r...
Scheme 7: Selected examples of inter- (A) and intramolecular (B) olefin hydroalkylations promoted by a silver...
Scheme 8: A) Intermolecular hydroalkylation of N-alkenyl β-ketoamides under Au(I) catalysis in the synthesis ...
Scheme 9: Asymmetric pyrrolidine synthesis through intramolecular hydroalkylation of α-substituted N-alkenyl ...
Scheme 10: Proposed mechanism for the chiral gold(I) complex promotion of the intermolecular olefin hydroalkyl...
Scheme 11: Selected examples of carbon quaternary center synthesis by gold and evidence of catalytic system pa...
Scheme 12: Synthesis of a spiro compound via an aza-Michael addition/olefin hydroalkylation cascade promoted b...
Scheme 13: A selected example of quaternary carbon center synthesis using an Fe(III) salt as a catalyst for th...
Scheme 14: Intermolecular hydroalkylation catalyzed by a cationic iridium complex (Fuji (2019) [47]).
Scheme 15: Generic example of an olefin hydrofunctionalization via MHAT (Shenvi (2016) [51]).
Scheme 16: The first examples of olefin hydrofunctionalization run under neutral conditions (Mukaiyama (1989) [56]...
Scheme 17: A) Aryl olefin dimerization catalyzed by vitamin B12 and triggered by HAT. B) Control experiment to...
Scheme 18: Generic example of MHAT diolefin cycloisomerization and possible competitive pathways. Shenvi (2014...
Scheme 19: Selected examples of the MHAT-promoted cycloisomerization reaction of unactivated olefins leading t...
Scheme 20: Regioselective carbocyclizations promoted by an MHAT process (Norton (2008) [76]).
Scheme 21: Selected examples of quaternary carbon centers synthetized via intra- (A) and intermolecular (B) MH...
Scheme 22: A) Proposed mechanism for the Fe(III)/PhSiH3-promoted radical conjugate addition between olefins an...
Scheme 23: Examples of cascade reactions triggered by HAT for the construction of trans-decalin backbone uniti...
Scheme 24: A) Selected examples of the MHAT-promoted radical conjugate addition between olefins and p-quinone ...
Scheme 25: A) MHAT triggered radical conjugate addition/E1cB/lactonization (in some cases) cascade between ole...
Scheme 26: A) Spirocyclization promoted by Fe(III) hydroalkylation of unactivated olefins. B) Simplified mecha...
Scheme 27: A) Selected examples of the construction of a carbon quaternary center by the MHAT-triggered radica...
Scheme 28: Hydromethylation of unactivated olefins under iron-mediated MHAT (Baran (2015) [95]).
Scheme 29: The hydroalkylation of unactivated olefins via iron-mediated reductive coupling with hydrazones (Br...
Scheme 30: Selected examples of the Co(II)-catalyzed bicyclization of dialkenylarenes through the olefin hydro...
Scheme 31: Proposed mechanism for the bicyclization of dialkenylarenes triggered by a MHAT process (Vanderwal ...
Scheme 32: Enantioconvergent cross-coupling between olefins and tertiary halides (Fu (2018) [108]).
Scheme 33: Proposed mechanism for the Ni-catalyzed cross-coupling reaction between olefins and tertiary halide...
Scheme 34: Proposed catalytic cycles for a MHAT/Ni cross-coupling reaction between olefins and halides (Shenvi...
Scheme 35: Selected examples of the hydroalkylation of olefins by a dual catalytic Mn/Ni system (Shenvi (2019) ...
Scheme 36: A) Selected examples of quaternary carbon center synthesis by reductive atom transfer; TBC: 4-tert-...
Scheme 37: A) Selected examples of quaternary carbon centers synthetized by radical addition to unactivated ol...
Scheme 38: A) Selected examples of organophotocatalysis-mediated radical polyene cyclization via a PET process...
Scheme 39: A) Sc(OTf)3-mediated carbocyclization approach for the synthesis of vicinal quaternary carbon cente...
Scheme 40: Scope of the Lewis acid-catalyzed methallylation of electron-rich styrenes. Method A: B(C6F5)3 (5.0...
Scheme 41: The proposed mechanism for styrene methallylation (Oestreich (2019) [123]).
Icilio Guareschi and his amazing “1897 reaction”
- Gian Cesare Tron,
- Alberto Minassi,
- Giovanni Sorba,
- Mara Fausone and
- Giovanni Appendino
Beilstein J. Org. Chem. 2021, 17, 1335–1351, doi:10.3762/bjoc.17.93
- observation was that the presence of radical traps, such as 4-hydroxy-substituted TEMPO, was detrimental for the reaction, which evidently involved free radicals. Anaerobic conditions (degassing with argon) inhibited the reaction, which could be restarted when oxygen was bubbled into the solution. This
Graphical Abstract
Figure 1: Icilio Guareschi (1847–1918). (Source: Annali della Reale Accademia di Agricoltura di Torino 1919, ...
Scheme 1: Vitamin B6 (pyridoxine, 1), gabapentin (2), and thymol (3).
Figure 2: Baliatico (Nursing) by Francesco Scaramuzza (275 cm × 214 cm, Parma, Complesso Museale della Pilott...
Figure 3: Schiff’s fictitious report on the foundation of the Gazzetta Chimica Italiana (Image reproduced fro...
Scheme 2: Reaction of thymol (3) with chloroform under the basic conditions of the Guareschi–Lustgarten react...
Figure 4: The chemistry building of Turin University in a historical picture. Note, that one of the “mysterio...
Scheme 3: Triacetonamine (6) and the related compounds phorone (7), α-eucaine (8), and tropinone (9).
Scheme 4: Taxonomy of the Guareschi pyridone syntheses.
Scheme 5: The catalytic cycle of the “1897 reaction”.
Scheme 6: Resonance forms of the radical 10.
Figure 5: The wet chamber used by Guareschi to restore parchments (Gorrini, G. L'incendio della R. Biblioteca...
Figure 6: The Guareschi mask. (Servizio Chimico Militare. L'opera di Icilio Guareschi precursore della masche...
Figure 7: Guareschi’s bust at the Dipartimento di Scienza e Tecnologia del Farmaco of Turin University. Permi...
An overview on disulfide-catalyzed and -cocatalyzed photoreactions
- Yeersen Patehebieke
Beilstein J. Org. Chem. 2020, 16, 1418–1435, doi:10.3762/bjoc.16.118
- ]. Conclusion In conclusion, under photoirradiation, organic disulfides can be easily cleaved into free radicals and can reversibly add to unsaturated multiple bonds to catalyze a variety of functionalization reactions under mild conditions. Disulfide-catalyzed oxidations of alkenes and alkynes are highly
Graphical Abstract
Scheme 1: [3 + 2] cyclization catalyzed by diaryl disulfide.
Scheme 2: [3 + 2] cycloaddition catalyzed by disulfide.
Scheme 3: Disulfide-bridged peptide-catalyzed enantioselective cycloaddition.
Scheme 4: Disulfide-catalyzed [3 + 2] methylenecyclopentane annulations.
Scheme 5: Disulfide as a HAT cocatalyst in the [4 + 2] cycloaddition reaction.
Scheme 6: Proposed mechanism of the [4 + 2] cycloaddition reaction using disulfide as a HAT cocatalyst.
Scheme 7: Disulfide-catalyzed ring expansion of vinyl spiro epoxides.
Scheme 8: Disulfide-catalyzed aerobic oxidation of diarylacetylene.
Scheme 9: Disulfide-catalyzed aerobic photooxidative cleavage of olefins.
Scheme 10: Disulfide-catalyzed aerobic oxidation of 1,3-dicarbonyl compounds.
Scheme 11: Proposed mechanism of the disulfide-catalyzed aerobic oxidation of 1,3-dicarbonyl compounds.
Scheme 12: Disulfide-catalyzed oxidation of allyl alcohols.
Scheme 13: Disulfide-catalyzed diboration of alkynes.
Scheme 14: Dehalogenative radical cyclization catalyzed by disulfide.
Scheme 15: Hydrodifluoroacetamidation of alkenes catalyzed by disulfide.
Scheme 16: Plausible mechanism of the hydrodifluoroacetamidation of alkenes catalyzed by disulfide.
Scheme 17: Disulfide-cocatalyzed anti-Markovnikov olefin hydration reactions.
Scheme 18: Disulfide-catalyzed decarboxylation of carboxylic acids.
Scheme 19: Proposed mechanism of the disulfide-catalyzed decarboxylation of carboxylic acids.
Scheme 20: Disulfide-catalyzed decarboxylation of carboxylic acids.
Scheme 21: Disulfide-catalyzed conversion of maleate esters to fumarates and 5H-furanones.
Scheme 22: Disulfide-catalyzed isomerization of difluorotriethylsilylethylene.
Scheme 23: Disulfide-catalyzed isomerization of allyl alcohols to carbonyl compounds.
Scheme 24: Proposed mechanism for the disulfide-catalyzed isomerization of allyl alcohols to carbonyl compound...
Scheme 25: Diphenyl disulfide-catalyzed enantioselective synthesis of ophirin B.
Scheme 26: Disulfide-catalyzed isomerization in the total synthesis of (+)-hitachimycin.
Scheme 27: Disulfide-catalyzed isomerization in the synthesis of (−)-gloeosporone.
Oxime radicals: generation, properties and application in organic synthesis
- Igor B. Krylov,
- Stanislav A. Paveliev,
- Alexander S. Budnikov and
- Alexander O. Terent’ev
Beilstein J. Org. Chem. 2020, 16, 1234–1276, doi:10.3762/bjoc.16.107
- reactions of oxime radicals. These reactions are classified into cyclizations involving C–H bond cleavage and cyclizations involving a double C=C bond cleavage. Keywords: iminoxyl radicals; isoxazolines; oxidative cyclization; oxime radicals; oximes; Introduction Free radicals in which an unpaired
- of free radicals (Scheme 9). It remains unchanged [45] when dissolved in styrene (2 hours, 25 °C) or vinyl acetate (20 minutes, 60 °C; conversion of the oxime radical was less than 10% after 3 days at 25 °C). The inertness of the di-tert-butyliminoxyl radical with respect to the mentioned substrates
Graphical Abstract
Figure 1: Imine-N-oxyl radicals (IV) discussed in the present review and other classes of N-oxyl radicals (I–...
Figure 2: The products of decomposition of iminoxyl radicals generated from oximes by oxidation with Ag2O.
Scheme 1: Generation of oxime radicals and study of the kinetics of their decay by photolysis of the solution...
Scheme 2: Synthesis of di-tert-butyliminoxyl radical and its decomposition products.
Scheme 3: The proposed reaction pathway of the decomposition of di-tert-butyliminoxyl radical (experimentally...
Scheme 4: Monomolecular decomposition of the tert-butyl(triethylmethyl)oxime radical.
Scheme 5: The synthesis and stability of the most stable dialkyl oxime radicals – di-tert-butyliminoxyl and d...
Scheme 6: The formation of iminoxyl radicals from β-diketones under the action of NO2.
Scheme 7: Synthesis of the diacetyliminoxyl radical.
Scheme 8: Examples of long-living oxime radicals with electron-withdrawing groups and the conditions for thei...
Figure 3: The electronic structure iminoxyl radicals and their geometry compared to the corresponding oximes.
Figure 4: Bond dissociation enthalpies (kcal/mol) of oximes and N,N-disubstituted hydroxylamines calculated o...
Scheme 9: Examples demonstrating the low reactivity of the di-tert-butyliminoxyl radical towards the substrat...
Scheme 10: The reactions of di-tert-butyliminoxyl radical with unsaturated hydrocarbons involving hydrogen ato...
Scheme 11: Possible mechanisms of reaction of di-tert-butyliminoxyl radical with alkenes.
Scheme 12: Products of the reaction between di-tert-butyliminoxyl radical and phenol derivatives.
Scheme 13: The reaction of di-tert-butyliminoxyl radical with amines.
Scheme 14: Reaction of di-tert-butyliminoxyl radicals with organolithium reagents.
Scheme 15: Cross-dehydrogenative C–O coupling of 1,3-dicarbonyl compounds with oximes under the action of mang...
Scheme 16: Cross-dehydrogenative C–O coupling of 1,3-dicarbonyl compounds with oximes under the action of Cu(BF...
Scheme 17: Oxidative C–O coupling of benzylmalononitrile (47) with 3-(hydroxyimino)pentane-2,4-dione (19).
Scheme 18: The proposed mechanism of the oxidative coupling of benzylmalononitrile (47) with diacetyl oxime (19...
Scheme 19: Oxidative C–O coupling of pyrazolones with oximes under the action of Fe(ClO4)3.
Scheme 20: The reaction of diacetyliminoxyl radical with pyrazolones.
Scheme 21: Oxidative C–O coupling of oximes with acetonitrile, ketones, and esters.
Scheme 22: Intramolecular cyclizations of oxime radicals to form substituted isoxazolines or cyclic nitrones.
Scheme 23: TEMPO-mediated oxidative cyclization of oximes with C–H bond cleavage.
Scheme 24: Proposed reaction mechanism of oxidative cyclization of oximes with C–H bond cleavage.
Scheme 25: Selectfluor/Bu4NI-mediated C–H oxidative cyclization of oximes.
Scheme 26: Oxidative cyclization of N-benzyl amidoximes to 1,2,4-oxadiazoles.
Scheme 27: The formation of quinazolinone 73a from 5-phenyl-4,5-dihydro-1,2,4-oxadiazole 74 under air.
Scheme 28: DDQ-mediated oxidative cyclization of thiohydroximic acids.
Scheme 29: Plausible mechanism of the oxidative cyclization of thiohydroximic acids.
Scheme 30: Silver-mediated oxidative cyclization of α-halogenated ketoximes and 1,3-dicarbonyl compounds.
Scheme 31: Possible pathway of one-pot oxidative cyclization of α-halogenated ketoximes and 1,3-dicarbonyl com...
Scheme 32: T(p-F)PPT-catalyzed oxidative cyclization of oximes with the formation of 1,2,4-oxadiazolines.
Scheme 33: Intramolecular cyclization of iminoxyl radicals involving multiple C=C and N=N bonds.
Scheme 34: Oxidative cyclization of β,γ- and γ,δ-unsaturated oximes employing the DEAD or TEMPO/DEAD system wi...
Scheme 35: Cobalt-catalyzed aerobic oxidative cyclization of β,γ-unsaturated oximes.
Scheme 36: Manganese-catalyzed aerobic oxidative cyclization of β,γ-unsaturated oximes.
Scheme 37: Visible light photocatalytic oxidative cyclization of β,γ-unsaturated oximes.
Scheme 38: TBAI/TBHP-mediated radical cascade cyclization of the β,γ-unsaturated oximes.
Scheme 39: TBAI/TBHP-mediated radical cascade cyclization of vinyl isocyanides with β,γ-unsaturated oximes.
Scheme 40: tert-Butylnitrite-mediated oxidative cyclization of unsaturated oximes with the introduction of an ...
Scheme 41: Transformation of unsaturated oxime to oxyiminomethylisoxazoline via the confirmed dimeric nitroso ...
Scheme 42: tert-Butylnitrite-mediated oxidative cyclization of unsaturated oximes with the introduction of a n...
Scheme 43: Synthesis of cyano-substituted oxazolines from unsaturated oximes using the TBN/[RuCl2(p-cymene)]2 ...
Scheme 44: Synthesis of trifluoromethylthiolated isoxazolines from unsaturated oximes.
Scheme 45: Copper-сatalyzed oxidative cyclization of β,γ-unsaturated oximes with the introduction of an azido ...
Scheme 46: TBHP-mediated oxidative cascade cyclization of β,γ-unsaturated oximes and unsaturated N-arylamides.
Scheme 47: Copper-сatalyzed oxidative cyclization of unsaturated oximes with the introduction of an amino grou...
Scheme 48: TEMPO-mediated oxidative cyclization of unsaturated oximes followed by elimination.
Scheme 49: Oxidative cyclization of β,γ-unsaturated oximes with the introduction of a trifluoromethyl group.
Scheme 50: Oxidative cyclization of unsaturated oximes with the introduction of a nitrile group.
Scheme 51: Oxidative cyclization of β,γ-unsaturated oximes to isoxazolines with the introduction of a nitrile ...
Scheme 52: Oxidative cyclization of β,γ-unsaturated oximes to isoxazolines with the introduction of a sulfonyl...
Scheme 53: Oxidative cyclization of β,γ- and γ,δ-unsaturated oximes to isoxazolines with the introduction of a...
Scheme 54: Oxidative cyclization of β,γ-unsaturated oximes to isoxazolines with the introduction of a thiocyan...
Scheme 55: PhI(OAc)2-mediated oxidative cyclization of oximes with C–S and C–Se bond formation.
Scheme 56: PhI(OAc)2-mediated oxidative cyclization of unsaturated oximes accompanied by alkoxylation.
Scheme 57: PhI(OAc)2-mediated cyclization of unsaturated oximes to methylisoxazolines.
Scheme 58: Oxidative cyclization-alkynylation of unsaturated oximes.
Scheme 59: TEMPO-mediated oxidative cyclization of C-glycoside ketoximes to C-glycosylmethylisoxazoles.
Scheme 60: Silver-сatalyzed oxidative cyclization of β,γ-unsaturated oximes with formation of fluoroalkyl isox...
Scheme 61: Oxidative cyclization of β,γ-unsaturated oximes with the formation of haloalkyl isoxazolines.
Scheme 62: Cyclization of β,γ-unsaturated oximes into haloalkyl isoxazolines under the action of the halogenat...
Scheme 63: Synthesis of haloalkyl isoxazoles and cyclic nitrones via oxidative cyclization and 1,2-halogen shi...
Scheme 64: Electrochemical oxidative cyclization of diaryl oximes.
Scheme 65: Copper-сatalyzed cyclization and dioxygenation oximes containing a triple C≡C bond.
Scheme 66: Photoredox-catalyzed sulfonylation of β,γ-unsaturated oximes by sulfonyl hydrazides.
Scheme 67: Oxidative cyclization of β,γ-unsaturated oximes with introduction of sulfonate group.
Scheme 68: Ultrasound-promoted oxidative cyclization of β,γ-unsaturated oximes.
Synthesis of pyrrolidinedione-fused hexahydropyrrolo[2,1-a]isoquinolines via three-component [3 + 2] cycloaddition followed by one-pot N-allylation and intramolecular Heck reactions
- Xiaoming Ma,
- Suzhi Meng,
- Xiaofeng Zhang,
- Qiang Zhang,
- Shenghu Yan,
- Yue Zhang and
- Wei Zhang
Beilstein J. Org. Chem. 2020, 16, 1225–1233, doi:10.3762/bjoc.16.106
- crispine A isolated from Carduus crispus L has antitumor activity [3]. Erythrina alkaloids have curare-like neuromuscular blocking activities [4], and also antioxidant activity against DPPH free radicals [5]. Lamellarins isolated from marine invertebrates [6] are inhibitors for HIV-1 integrase and also
Graphical Abstract
Figure 1: Bioactive pyrrolo[2,1-a]isoquinolines and hexahydropyrrolo[2,1-a]isoquinolines.
Scheme 1: [3 + 2] Cycloaddition with amino esters or amino acids.
Scheme 2: Scaffolds derived from the initial [3 + 2] adducts.
Scheme 3: [3 + 2] Cycloaddition with amino esters or amino acids. Conditions: 1:3:4 (1.2:1:1.1), Et3N (1.5 eq...
Scheme 4: Synthesis of pyrrolo[2,1-a]isoquinolines 9. Reaction conditions: 5 (0.5 mmol, 1 equiv), 7 (3 equiv)...
Scheme 5: Synthesis of pyrrolo[2,1-a]isoquinolines 11. Reaction conditions: 6 (0.5 mmol, 1 equiv), 7 (3 equiv...
Scheme 6: Synthesis of pyrrolo[2,1-a]isoquinolines 12. Reaction conditions: 5 or 6 (0.5 mmol, 1 equiv), cinna...
Scheme 7: Plausible mechanism for the synthesis of 9a.
Insertion of [1.1.1]propellane into aromatic disulfides
- Robin M. Bär,
- Gregor Heinrich,
- Martin Nieger,
- Olaf Fuhr and
- Stefan Bräse
Beilstein J. Org. Chem. 2019, 15, 1172–1180, doi:10.3762/bjoc.15.114
- , which was opened with free radicals in most cases. The reaction with diacetyl and subsequent oxidation leads to the important intermediate bicyclo[1.1.1]pentane-1,3-dicarboxylic acid which provides access to unsymmetrically substituted BCPs (not shown) [13]. It is assumed that the reaction of 1 with
Graphical Abstract
Scheme 1: Summary of the most recent methods to obtain different BCPs from 1.
Scheme 2: Screening reaction performed with different types of irradiation (see Figure 1).
Figure 1: Optimization of the reaction conditions. The relative conversion was determined by GC–MS. The use o...
Figure 2: Molecular structure of 6a (displacement parameters are drawn at 50% probability level), distance C1...
Scheme 3: Proposed mechanism of the propellane insertion into disulfide bonds.
Scheme 4: The insertion of 1 into dibenzyl disulfide (12) led to the formation of BCP 13 and traces of [2]sta...
Scheme 5: Reaction of propellane (1) with the two disulfides 10a and 10d. When two different disulfides were ...
Figure 3: NMR spectra of pure 6a (green) and 6d (red) and the obtained mixture with the new compound 15 (blue...
Scheme 6: The reaction of 1 with the two disulfides 10a and 10e led to the known products 6a, 6e and to the u...
Photochemical generation of the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radical from caged nitroxides by near-infrared two-photon irradiation and its cytocidal effect on lung cancer cells
- Ayato Yamada,
- Manabu Abe,
- Yoshinobu Nishimura,
- Shoji Ishizaka,
- Masashi Namba,
- Taku Nakashima,
- Kiyofumi Shimoji and
- Noboru Hattori
Beilstein J. Org. Chem. 2019, 15, 863–873, doi:10.3762/bjoc.15.84
- new caged nitroxides (nitroxide donors) 2a and 2b having the TP-responsive NPBF chromophore and the NIR TP-triggered generation of the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radical under atmospheric conditions using these species (Scheme 1). Because free radicals are cytotoxic due to their
- strong DNA-damaging activity [65], they play important roles as anticancer therapeutic agents [66]. Among the free radicals, nitroxides including the TEMPO radical have unique properties, where they can act not only as radical scavengers, but also as anticancer agents [67]. Due to the unique properties
- above, the spatiotemporally controlled generation of the radical pair of TEMPO and BR was confirmed in the photolysis of compounds 2a and 2b. Because free radicals play important roles as anticancer therapeutic agents, the cytocidal effect of the radical released from compound 2a was also tested in
Graphical Abstract
Scheme 1: Photochemical generation of TEMPO radical.
Scheme 2: Synthesis of caged nitroxides 2a and 2b.
Figure 1: Photochemical generation of TEMPO from 2a and 2b. EPR spectra acquired during the photolysis of 2a ...
Figure 2: Time profile for photochemical generation of TEMPO radical from 2 (5 mM) at ≈298 K in benzene: (a) ...
Scheme 3: Photochemical generation of TEMPO radical and photoproducts 6 and 7 under air atmosphere.
Figure 3: Time profile, ln([2a]/[2a]0) versus irradiation time, of two-photon uncaging reaction of TEMPO in t...
Figure 4: ESR spectra acquired during the photolysis of 2a (5 mM) in benzene using 365 nm light.
Scheme 4: Isodesmic reaction from BRa and 5b to 5a and BRb.
Figure 5: Irradiation time-dependent decline in viability of LLC cells with compound 2a.
Figure 6: Detection of intracellular ROS only in irradiated LLC cells with 2a-containing medium.
Synthesis of polydicyclopentadiene using the Cp2TiCl2/Et2AlCl catalytic system and thin-layer oxidation of the polymer in air
- Zhargolma B. Bazarova,
- Ludmila S. Soroka,
- Alex A. Lyapkov,
- Мekhman S. Yusubov and
- Francis Verpoort
Beilstein J. Org. Chem. 2019, 15, 733–745, doi:10.3762/bjoc.15.69
- chain process of PDCPD oxidation follows. Various mechanisms of chain initiation are possible, e.g., the formation of primary free radicals initiating the chain reaction of polymer oxidation (Equation 1). More often, the chain initiation step is described as a bimolecular interaction between oxygen and
Graphical Abstract
Figure 1: Absorption spectra in the UV and visible spectral region: 1) bis(cyclopentadienyl)titan dichloride (...
Figure 2: Absorption spectra in the visible spectral region: 1) Cp2TiCl2·AlEt2Cl (toluene, 10 mmol/L, Ti/Al r...
Figure 3: 1Н NMR spectra of tricyclopentadiene (a) and the interaction product between Cp2TiCl2 and AlEt2Cl w...
Scheme 1: Mechanism of alkylation of Cp2TiCl2.
Figure 4: Visible spectra of a mixture of Cp2TiCl2 and AlEt2Cl as function of time.
Figure 5: Thermometric curve of DCPD polymerization using the catalyst system based on Cp2TiCl2 (a) and its s...
Scheme 2: The structures formed as a result of the cationic polymerization of dicyclopentadiene.
Scheme 3: The units resulting from ROMP of dicyclopentadiene.
Scheme 4: Mechanism of ROMP dicyclopentadiene.
Figure 6: FTIR spectrum of PDCPD obtained in toluene with the catalyst system based on Cp2TiCl2 and AlEt2Cl.
Figure 7: 1Н NMR spectrum of PDCPD obtained with the catalytic system based on Cp2TiCl2 and AlEt2Cl.
Figure 8: GPC traces for two samples of DCPD polymers obtained at a concentration of Cp2TiCl2/AlEt2Cl complex...
Figure 9: IR spectra of cationic polymerized dicyclopentadiene taken after certain periods of time exposed to...
Figure 10: Correlation of intensities of vibrational bands at 1620 and 700 cm−1 and layer exposure time in air...
Figure 11: DSC exotherm for PDCPD subjected to air oxidation for 700 hours.
Figure 12: DSC exotherm for PDCPD subjected to unexposed film: 1) in air atmosphere; 2) in argon.
Scheme 5: Possible radical formation in the reaction (1).
Scheme 6: The first step of the chain propagation.
Figure 13: Dependence of intensities of adsorption bands at 1410 and 700 cm−1 and dwell time of the layer in a...
Figure 14: Semi-logarithmic kinetic curve of PDCPD oxidation in air (thin layer on silicon) with respect to in...
Figure 15: The distribution of oxygen concentration in the polymer layer: 1 – a layer of oxidized cross-linked...
Figure 16: Dependence of the ratio of adsorption bands at 1700 and 700 cm−1 on the exposure time of the layer ...
Figure 17: Infrared spectra (a) of products of cationic polymerization of DCPD, stabilized with an antioxidant...
Oxidative radical ring-opening/cyclization of cyclopropane derivatives
- Yu Liu,
- Qiao-Lin Wang,
- Zan Chen,
- Cong-Shan Zhou,
- Bi-Quan Xiong,
- Pan-Liang Zhang,
- Chang-An Yang and
- Quan Zhou
Beilstein J. Org. Chem. 2019, 15, 256–278, doi:10.3762/bjoc.15.23
- of sufficient interest for the scientific community to further advance the application of oxidative radical strategies in the ring-opening/cyclization of cyclopropane derivatives. Keywords: cyclopropane derivatives; free radicals; ring-opening/cyclization; Introduction Cyclopropane is a cycloalkane
Graphical Abstract
Scheme 1: The oxidative radical ring-opening/cyclization of cyclopropane derivatives.
Scheme 2: Mn(OAc)3-mediated oxidative radical ring-opening and cyclization of MCPs with malonates.
Scheme 3: Mn(III)-mediated oxidative radical ring-opening and cyclization of MCPs with 1,3-dicarbonyl compoun...
Scheme 4: Heat-promoted ring-opening/cyclization of MCPs with elemental chalgogens.
Scheme 5: Copper(II) acetate-mediated oxidative radical ring-opening and cyclization of MCPs with diphenyl di...
Scheme 6: AIBN-promoted oxidative radical ring-opening and cyclization of MCPs with benzenethiol.
Scheme 7: AIBN-mediated oxidative radical ring-opening and cyclization of MCPs with diethyl phosphites.
Scheme 8: Organic-selenium induced radical ring-opening and cyclization of MCPs derivatives (cyclopropylaldeh...
Scheme 9: Copper(I)-catalyzed oxidative radical trifluoromethylation/ring-opening/cyclization of MCPs with To...
Scheme 10: Ag(I)-mediated trifluoromethylthiolation/ring-opening/cyclization of MCPs with AgSCF3.
Scheme 11: oxidative radical ring-opening and cyclization of MCPs with α-C(sp3)-–H of ethers.
Scheme 12: Oxidative radical ring-opening and cyclization of MCPs with aldehydes.
Scheme 13: Cu(I) or Fe(II)-catalyzed oxidative radical trifluoromethylation/ring-opening/cyclization of MCPs d...
Scheme 14: Rh(II)-catalyzed oxidative radical ring-opening and cyclization of MCPs.
Scheme 15: Ag(I)-catalyzed oxidative radical amination/ring-opening/cyclization of MCPs derivatives.
Scheme 16: Heating-promoted radical ring-opening and cyclization of MCP derivatives (arylvinylidenecyclopropan...
Scheme 17: Bromine radical-mediated ring-opening of alkylidenecyclopropanes.
Scheme 18: Fluoroalkyl (Rf) radical-mediated ring-opening of MCPs.
Scheme 19: Visible-light-induced alkylation/ring-opening/cyclization of cyclopropyl olefins with bromides.
Scheme 20: Mn(III)-mediated ring-opening and [3 + 3]-annulation of cyclopropanols and vinyl azides.
Scheme 21: Ag(I)-catalyzed oxidative ring-opening of cyclopropanols with quinones.
Scheme 22: Ag(I)-catalyzed oxidative ring-opening of cyclopropanols with heteroarenes.
Scheme 23: Cu(I)-catalyzed oxidative ring-opening/trifluoromethylation of cyclopropanols.
Scheme 24: Cu(I)-catalyzed oxidative ring-opening and trifluoromethylation/trifluoromethylthiolation of cyclop...
Scheme 25: Ag(I)-mediated oxidative ring-opening/fluorination of cyclopropanols with Selectfluor.
Scheme 26: Photocatalyzed ring-opening/fluorination of cyclopropanols with Selectfluor.
Scheme 27: Na2S2O8-promoted ring-opening/alkynylation of cyclopropanols with EBX.
Scheme 28: Ag(I)-catalyzed ring-opening and chlorination of cyclopropanols with aldehydes.
Scheme 29: Ag(I)-catalyzed ring-opening/alkynylation of cyclopropanols with EBX.
Scheme 30: Na2S2O8-promoted ring-opening/alkylation of cyclopropanols with acrylamides.
Scheme 31: Cyclopropanol ring-opening initiated tandem cyclization with acrylamides or 2-isocyanobiphenyls.
Scheme 32: Ag(II)-mediated oxidative ring-opening/fluorination of cyclopropanols with AgF2.
Scheme 33: Cu(II)-catalyzed ring-opening/fluoromethylation of cyclopropanols with sulfinate salts.
Scheme 34: Cu(II)-catalyzed ring-opening/sulfonylation of cyclopropanols with sulfinate salts.
Scheme 35: Na2S2O8-promoted ring-opening/arylation of cyclopropanols with propiolamides.
Scheme 36: The ring-opening and [3 + 2]-annulation of cyclopropanols with α,β-unsaturated aldehydes.
Scheme 37: Cu(II)-catalyzed ring-opening/arylation of cyclopropanols with aromatic nitrogen heterocyles.
Scheme 38: Ag(I)-catalyzed ring-opening and difluoromethylthiolation of cyclopropanols with PhSO2SCF2H.
Scheme 39: Ag(I)-catalyzed ring-opening and acylation of cyclopropanols with aldehydes.
Scheme 40: Aerobic oxidation ring-opening of cyclopropanols for the synthesis of 2-oxyranyl ketones.
Scheme 41: Aerobic oxidation ring-opening of cyclopropanols for the synthesis of linear enones.
Scheme 42: Aerobic oxidation ring-opening of cyclopropanols for the synthesis of metabolite.
Organometallic vs organic photoredox catalysts for photocuring reactions in the visible region
- Aude-Héloise Bonardi,
- Frédéric Dumur,
- Guillaume Noirbent,
- Jacques Lalevée and
- Didier Gigmes
Beilstein J. Org. Chem. 2018, 14, 3025–3046, doi:10.3762/bjoc.14.282
- with the monomer or a monomer blend. The PI is a component which absorbs light and initiates polymerization alone whereas a photoinitiating system comprises different compounds [8][9][10]. Under irradiation, PI or PIs generate active species: free radicals and/or ions and/or acid. When the active
Graphical Abstract
Figure 1: Typical oxidative and reductive cycle for a photoredox catalyst (PC).
Figure 2: Transitions involved in absorbing species containing π, σ and n electrons.
Figure 3: Ligand to metal charge transfer (illustrated here for a d6 metal complex).
Figure 4: Metal to ligand charge transfer (illustrated here for a d5 metal complex).
Scheme 1: Structures of additives involved in the photoredox catalytic cycles.
Figure 5: Catalytic cycles involved with iodonium salt and (A) (TMS)3SiH, (B) NVK and (C) EDB.
Scheme 2: Structures of photoredox metal-based catalysts.
Scheme 3: Photocatalytical cycle for the Ru complex.
Scheme 4: Structures of photoredox organocatalysts.
Scheme 5: Diversity of the chemical structures of photoredox organocatalysts.
Scheme 6: Structures of benchmarked monomers.
Scheme 7: Structure of the CARET additive.
Scheme 8: Photoredox catalysis mechanism of a visible light-mediated living radical polymerization. (Abbrevia...
Learning from B12 enzymes: biomimetic and bioinspired catalysts for eco-friendly organic synthesis
- Keishiro Tahara,
- Ling Pan,
- Toshikazu Ono and
- Yoshio Hisaeda
Beilstein J. Org. Chem. 2018, 14, 2553–2567, doi:10.3762/bjoc.14.232
- ligand. B12 is reduced to Co(I) species in the active center by reductases in sustainable processes. The partially π-conjugated system of the corrin ring is less easy to be adducted by free radicals than those of porphyrins. B12 is bound to a number of proteins and acts as a module. Different chemical
- electrochemical reduction. In addition, the corrin-ring of the B12 derivatives is tolerant to free radicals, as described above. Thus, alkylated complexes have been used for radical-mediated organic synthesis such as halide coupling, alkene coupling, and addition to double bonds [7][26][27]. In particular, the Co
Graphical Abstract
Figure 1: (a) Structure and (b) reactivity of B12.
Figure 2: (a) Schematic representation of B12 enzyme-involving systems. (b) Construction of biomimetic and bi...
Scheme 1: (a) Carbon-skeleton rearrangement mediated by a coenzyme B12-depenedent enzyme. (b) Electrochemical...
Scheme 2: Electrochemical carbon-skeleton arrangements mediated by B12 model complexes.
Figure 3: Key electrochemical reactivity of 1 and 2 in methylated forms.
Scheme 3: Carbon-skeleton arrangements mediated by B12-vesicle artificial enzymes.
Scheme 4: Carbon-skeleton arrangements mediated by B12-HSA artificial enzymes.
Scheme 5: Photochemical carbon-skeleton arrangements mediated by B12-Ru@MOF.
Scheme 6: (a) Methyl transfer reaction mediated by B12-dependent methionine synthase. (b) Methyl transfer rea...
Scheme 7: Methyl transfer reaction for the detoxification of inorganic arsenics.
Scheme 8: (a) Dechlorination of 1,1,2,2-tetrarchloroethene mediated by a reductive dehalogenase. (b) Electroc...
Scheme 9: Visible-light-driven dechlorination of DDT using 1 in the presence of photosensitizers.
Scheme 10: 1,2-Migration of a phenyl group mediated by the visible-light-driven catalytic system composed of 1...
Scheme 11: Ring-expansion reactions mediated by the B12-TiO2 hybrid catalyst with UV-light irradiation.
Scheme 12: Trifluoromethylation and perfluoroalkylation of aromatic compounds achieved through electrolysis wi...
Hypervalent iodine compounds for anti-Markovnikov-type iodo-oxyimidation of vinylarenes
- Igor B. Krylov,
- Stanislav A. Paveliev,
- Mikhail A. Syroeshkin,
- Alexander A. Korlyukov,
- Pavel V. Dorovatovskii,
- Yan V. Zubavichus,
- Gennady I. Nikishin and
- Alexander O. Terent’ev
Beilstein J. Org. Chem. 2018, 14, 2146–2155, doi:10.3762/bjoc.14.188
- . It was shown that the iodine atom in the prepared iodo-oxyimides can be substituted by various nucleophiles. Keywords: free radicals; hypervalent iodine; imide-N-oxyl radicals; iodination; N-hydroxyimides; oxidative functionalization; Introduction The presented work opens a new chapter in the
Graphical Abstract
Scheme 1: Difunctionalization of double C=C bond with the formation of C–O and C–I bonds.
Scheme 2: Iodo-oxyimidation of styrenes 1a–k with preparation of products 3aa–ka, 3ab–db, 3fb, 3hb, and 3kb.
Figure 1: Scope of the iodo-oxyimidation of vinylarenes with I2/PhI(OAc)2 system. Reaction conditions: vinyla...
Figure 2: Molecular structure of 3ca. Atoms are presented as anisotropic displacement parameters (ADP) ellips...
Scheme 3: The proposed mechanism of iodo-oxyimidation of styrene (1a) using the NHPI/I2/PhI(OAc)2 system with...
Figure 3: CV curves of styrene (1a, purple), NHPI (2a, red), I2 (blue) and PhI(OAc)2 (green) in 0.1 M n-Bu4NBF...
Scheme 4: Gram-scale synthesis of compound 3aa.
Scheme 5: Synthetic utility of the iodo-oxyimides 3aa and 3ab.
Visible light-mediated difluoroalkylation of electron-deficient alkenes
- Vyacheslav I. Supranovich,
- Vitalij V. Levin,
- Marina I. Struchkova,
- Jinbo Hu and
- Alexander D. Dilman
Beilstein J. Org. Chem. 2018, 14, 1637–1641, doi:10.3762/bjoc.14.139
- hydrogen and as a trigger for the generation of free radicals mediated by visible light. Difluoroalkylation of alkenes. Isolated yields are shown. a2 equiv of the alkene were used. Fluoroalkylation of alkenes. Proposed mechanism. Optimization studies. Supporting Information Supporting Information File 220
Graphical Abstract
Scheme 1: Fluoroalkylation of alkenes.
Figure 1: Difluoroalkylation of alkenes. Isolated yields are shown. a2 equiv of the alkene were used.
Scheme 2: Proposed mechanism.
