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Search for "oxidant" in Full Text gives 356 result(s) in Beilstein Journal of Organic Chemistry. Showing first 200.
The biomimetic synthesis of balsaminone A and ellagic acid via oxidative dimerization
- Sharna-kay Daley and
- Nadale Downer-Riley
Beilstein J. Org. Chem. 2020, 16, 2026–2031, doi:10.3762/bjoc.16.169
- aqueous conditions to prevent complexation of the reagent and the starting material. Of the Lewis acids used, stannic chloride proved to be the most effective oxidant for dimerization (Table 1). However, the hypervalent iodine reagents PIFA and PIDA gave better results overall, affording dimer 18 in 63
Graphical Abstract
Figure 1: Selected natural products synthesized via oxidative dimerization.
Scheme 1: Proposed biosynthesis of balsaminone A (4) [19].
Scheme 2: Proposed biosynthesis of ellagic acid (5) [20].
Scheme 3: Previous syntheses of balsaminone A (4) [22] and ellagic acid (5) [23].
Scheme 4: Attempted synthesis of the biomimetic precursor 9. [O]: Act-C, K3[Fe(CN)6], or p-benzoquinone.
Scheme 5: Biomimetic synthesis of balsaminone A (4).
Scheme 6: Concise and efficient biomimetic synthesis of ellagic acid (5).
Metal-free synthesis of phosphinoylchroman-4-ones via a radical phosphinoylation–cyclization cascade mediated by K2S2O8
- Qiang Liu,
- Weibang Lu,
- Guanqun Xie and
- Xiaoxia Wang
Beilstein J. Org. Chem. 2020, 16, 1974–1982, doi:10.3762/bjoc.16.164
- motifs were conveniently synthesized from readily available diphenylphosphine oxides and alkenyl aldehydes via a metal-free tandem phosphinoylation/cyclization protocol. The reaction utilizes K2S2O8 as oxidant and proceeds in DMSO/H2O at environmentally benign conditions with a broad substrate scope and
- 1a). Besides, in 2016 Li’s group [28] reported a silver-catalyzed straightforward approach for the synthesis of phosphonate-functionalized chroman-4-ones via a phosphoryl radical-initiated cascade cyclization of 2-(allyloxy)arylaldehydes using K2S2O8 as an oxidant, however, diphenylphosphine oxide
- employing 2-(allyloxy)benzaldehyde (1a) and diphenylphosphine oxide (DPPO, 2a) as the model substrates with K2S2O8 as the oxidant, which is a cheap, readily available, and versatile oxidant. On the basis of literature reports [29][30] and our continuing interest in green chemistry [31][32], we set the
Graphical Abstract
Figure 1: Biologically active compounds featuring the chroman-4-one framework.
Scheme 1: Methods to produce phosphonate-substituted chroman-4-ones.
Figure 2: X-ray structure of compound 3aa (CCDC 2002878).
Scheme 2: Scope of 2-(allyloxy)arylaldehydes. Reaction conditions: 1 (0.3 mmol, 1 equiv), 2a (1.5 equiv) [2f ...
Scheme 3: Scope of diphenylphosphine oxides. Reaction conditions: 1a (0.3 mmol, 1 equiv), 2 (1.5 equiv), DMSO...
Scheme 4: Gram-scale reaction.
Scheme 5: Control experiments and proposed mechanism.
When metal-catalyzed C–H functionalization meets visible-light photocatalysis
- Lucas Guillemard and
- Joanna Wencel-Delord
Beilstein J. Org. Chem. 2020, 16, 1754–1804, doi:10.3762/bjoc.16.147
- activation, a catalytic amount of a transition metal (generally Pd, Rh and Ru) is frequently used in combination with a stoichiometric amount of an external oxidant (typically Cu or Ag salts). Such additional oxidants are required if transiently produced low-valent metal complexes need to be reoxidized by
- , together with a metal hydride or a low-valent metal complex. Hence, in order to reoxidize the metal catalyst, excess of an external oxidant, such as Cu(II) or Ag(I) salts, was frequently used. On the other hand, photoredox catalysis has been mainly employed for electron-transfer reactions and, remarkably
- selecting judiciously a PC with adequate redox potentials, the ground state of the latter could be regenerated by means of a mild and abundant oxidant such as molecular oxygen. The overall process thus allowed the replacement of stoichiometric amounts of external oxidants with a suitable PC. Following this
Graphical Abstract
Figure 1: Concept of dual synergistic catalysis.
Figure 2: Classification of catalytic systems involving two catalysts.
Figure 3: General mechanism for the dual nickel/photoredox catalytic system.
Figure 4: General mechanisms for C–H activation catalysis involving different reoxidation strategies.
Figure 5: Indole synthesis via dual C–H activation/photoredox catalysis.
Figure 6: Proposed mechanism for the indole synthesis via dual catalysis.
Figure 7: Oxidative Heck reaction on arenes via the dual catalysis.
Figure 8: Proposed mechanism for the Heck reaction on arenes via dual catalysis.
Figure 9: Oxidative Heck reaction on phenols via the dual catalysis.
Figure 10: Proposed mechanism for the Heck reaction on phenols via dual catalysis.
Figure 11: Carbazole synthesis via dual C–H activation/photoredox catalysis.
Figure 12: Proposed mechanism for the carbazole synthesis via dual catalysis.
Figure 13: Carbonylation of enamides via the dual C–H activation/photoredox catalysis.
Figure 14: Proposed mechanism for carbonylation of enamides via dual catalysis.
Figure 15: Annulation of benzamides via the dual C–H activation/photoredox catalysis.
Figure 16: Proposed mechanism for the annulation of benzamides via dual catalysis.
Figure 17: Synthesis of indoles via the dual C–H activation/photoredox catalysis.
Figure 18: Proposed mechanism for the indole synthesis via dual catalysis.
Figure 19: General concept of dual catalysis merging C–H activation and photoredox catalysis.
Figure 20: The first example of dual catalysis merging C–H activation and photoredox catalysis.
Figure 21: Proposed mechanism for the C–H arylation with diazonium salts via dual catalysis.
Figure 22: Dual catalysis merging C–H activation/photoredox using diaryliodonium salts.
Figure 23: Direct arylation via the dual catalytic system reported by Xu.
Figure 24: Direct arylation via dual catalytic system reported by Balaraman.
Figure 25: Direct arylation via dual catalytic system reported by Guo.
Figure 26: C(sp3)–H bond arylation via the dual Pd/photoredox catalytic system.
Figure 27: Acetanilide derivatives acylation via the dual C–H activation/photoredox catalysis.
Figure 28: Proposed mechanism for the C–H acylation with α-ketoacids via dual catalysis.
Figure 29: Acylation of azobenzenes via the dual catalysis C–H activation/photoredox.
Figure 30: C2-acylation of indoles via the dual C–H activation/photoredox catalysis.
Figure 31: Proposed mechanism for the C2-acylation of indoles with aldehydes via dual catalysis.
Figure 32: C2-acylation of indoles via the dual C–H activation/photoredox catalysis.
Figure 33: Perfluoroalkylation of arenes via the dual C–H activation/photoredox catalysis.
Figure 34: Proposed mechanism for perfluoroalkylation of arenes via dual catalysis.
Figure 35: Sulfonylation of 1-naphthylamides via the dual C–H activation/photoredox catalysis.
Figure 36: Proposed mechanism for sulfonylation of 1-naphthylamides via dual catalysis.
Figure 37: meta-C–H Alkylation of arenes via visible-light metallaphotocatalysis.
Figure 38: Alternative procedure for meta-C–H alkylation of arenes via metallaphotocatalysis.
Figure 39: Proposed mechanism for meta-C–H alkylation of arenes via metallaphotocatalysis.
Figure 40: C–H borylation of arenes via visible-light metallaphotocatalysis.
Figure 41: Proposed mechanism for C–H borylation of arenes via visible-light metallaphotocatalysis.
Figure 42: Undirected C–H aryl–aryl cross coupling via dual gold/photoredox catalysis.
Figure 43: Proposed mechanism for the undirected C–H aryl–aryl cross-coupling via dual catalysis.
Figure 44: Undirected C–H arylation of (hetero)arenes via dual manganese/photoredox catalysis.
Figure 45: Proposed mechanism for the undirected arylation of (hetero)arenes via dual catalysis.
Figure 46: Photoinduced C–H arylation of azoles via copper catalysis.
Figure 47: Photo-induced C–H chalcogenation of azoles via copper catalysis.
Figure 48: Decarboxylative C–H adamantylation of azoles via dual cobalt/photoredox catalysis.
Figure 49: Proposed mechanism for the C–H adamantylation of azoles via dual catalysis.
Figure 50: General mechanisms for the “classical” (left) and Cu-free variant (right) Sonogoshira reaction.
Figure 51: First example of a dual palladium/photoredox catalysis for Sonogashira-type couplings.
Figure 52: Arylation of terminal alkynes with diazonium salts via dual gold/photoredox catalysis.
Figure 53: Proposed mechanism for the arylation of terminal alkynes via dual catalysis.
Figure 54: C–H Alkylation of alcohols promoted by H-atom transfer (HAT).
Figure 55: Proposed mechanism for the C–H alkylation of alcohols promoted by HAT.
Figure 56: C(sp3)–H arylation of latent nucleophiles promoted by H-atom transfer.
Figure 57: Proposed mechanism for the C(sp3)–H arylation of latent nucleophiles promoted by HAT.
Figure 58: Direct α-arylation of alcohols promoted by H-atom transfer.
Figure 59: Proposed mechanism for the direct α-arylation of alcohols promoted by HAT.
Figure 60: C–H arylation of amines via dual Ni/photoredox catalysis.
Figure 61: Proposed mechanism for the C–H arylation of amines via dual Ni/photoredox catalysis.
Figure 62: C–H functionalization of nucleophiles via excited ketone/nickel dual catalysis.
Figure 63: Proposed mechanism for the C–H functionalization enabled by excited ketones.
Figure 64: Selective sp3–sp3 cross-coupling promoted by H-atom transfer.
Figure 65: Proposed mechanism for the selective sp3–sp3 cross-coupling promoted by HAT.
Figure 66: Direct C(sp3)–H acylation of amines via dual Ni/photoredox catalysis.
Figure 67: Proposed mechanism for the C–H acylation of amines via dual Ni/photoredox catalysis.
Figure 68: C–H hydroalkylation of internal alkynes via dual Ni/photoredox catalysis.
Figure 69: Proposed mechanism for the C–H hydroalkylation of internal alkynes.
Figure 70: Alternative procedure for the C–H hydroalkylation of ynones, ynoates, and ynamides.
Figure 71: Allylic C(sp3)–H activation via dual Ni/photoredox catalysis.
Figure 72: Proposed mechanism for the allylic C(sp3)–H activation via dual Ni/photoredox catalysis.
Figure 73: Asymmetric allylation of aldehydes via dual Cr/photoredox catalysis.
Figure 74: Proposed mechanism for the asymmetric allylation of aldehydes via dual catalysis.
Figure 75: Aldehyde C–H functionalization promoted by H-atom transfer.
Figure 76: Proposed mechanism for the C–H functionalization of aldehydes promoted by HAT.
Figure 77: Direct C–H arylation of strong aliphatic bonds promoted by HAT.
Figure 78: Proposed mechanism for the C–H arylation of strong aliphatic bonds promoted by HAT.
Figure 79: Direct C–H trifluoromethylation of strong aliphatic bonds promoted by HAT.
Figure 80: Proposed mechanism for the C–H trifluoromethylation of strong aliphatic bonds.
Fluorohydration of alkynes via I(I)/I(III) catalysis
- Jessica Neufeld,
- Constantin G. Daniliuc and
- Ryan Gilmour
Beilstein J. Org. Chem. 2020, 16, 1627–1635, doi:10.3762/bjoc.16.135
- organocatalyst, Selectfluor® was employed as the terminal oxidant, and an amine/HF complex enlisted as the fluoride source (please see Supporting Information File 1 for full details). The reaction was performed in CHCl3 at ambient temperature and the crude reaction mixtures were analysed by 19F NMR spectroscopy
- (50% yield), ground Oxone® or N-pyridine oxide proved to be ineffective (Table 1, entries 9–11). Increasing the reaction temperature to 50 °C led to the same outcome as at ambient temperature (64% yield, Table 1, entry 12). Finally, the control reactions in the absence of catalyst, oxidant and HF
Graphical Abstract
Figure 1: (A) Synthetic routes to α-fluoroketones from silyl enol ethers or acetophenone derivatives. (B) Sel...
Scheme 1: Substrate scope with standard reaction conditions: alkyne (0.2 mmol), p-TolI (20 mol %), Selectfluor...
Figure 2: X-ray molecular structure of compound 2. Conformation of the carbonyl group and the fluoride with a...
Figure 3: (A) Structure activity relationship of the core scaffold. (B) Exploring the effect of methyl benzoa...
Figure 4: (A) Hammett plot varying the para-substitution on the alkyne (ρ ≈ 0). (B) Hammett plot varying the ...
Figure 5: An overview of the I(I)/I(III)-catalysed fluorohydration of alkynes.
Facile synthesis of 7-alkyl-1,2,3,4-tetrahydro-1,8-naphthyridines as arginine mimetics using a Horner–Wadsworth–Emmons-based approach
- Rhys A. Lippa,
- John A. Murphy and
- Tim N. Barrett
Beilstein J. Org. Chem. 2020, 16, 1617–1626, doi:10.3762/bjoc.16.134
- occur via a radical pathway. When iodide 29 was replaced by a superior oxidant in 1,2-dibromoethane, formation of dimer 32 increased (17% isolated yield). This supports the previously reported proposals that dimerisation occurs via single-electron oxidation of the 2-picolyl anion by the halide
- /pseudohalide oxidant followed by recombination of the resulting picolyl radical [28][29][30]. Whilst trace oxygen may be involved, as indicated by the presence of alcohol 31, no dimerisation or alcohol formation was seen in the absence of a halide/pseudohalide-based oxidant, during C-phosphorylation or
Graphical Abstract
Figure 1: The Arg–Gly–Asp tripeptide sequence and examples of tetrahydro-1,8-naphthyridine-containing integri...
Scheme 1: Commonly used synthetic routes to tetrahydro-1,8-naphthyridine moieties by hydrogenation of saturat...
Scheme 2: Previous synthetic route to fluoropyrrolidine 6 utilising a Wittig reaction and the novel, higher y...
Scheme 3: Synthesis of phosphoramidate 9 from tetrahydro-1,8-naphthyridine 8. Conditions: s-BuLi (3 equiv), d...
Scheme 4: Mono- and diphosphorylation of tetrahydro-1,8-naphthyridine 11. Conditions: (i) s-BuLi (2 equiv), d...
Scheme 5: Synthesis of amine 6 from phosphonate 7 and aldehyde 5. Conditions: (i) T3P® (50% w/w in DCM, 3 equ...
Scheme 6: Monodeuteration of 13 as observed by 1H and 13C NMR. Conditions: s-BuLi (3 equiv), THF, −42 °C, 20 ...
Scheme 7: Sequential diphosphorylation of tetrahydronaphthyridine 11. Conditions: (i) iPrMgCl (1.5 equiv), TH...
Scheme 8: Possible mechanistic pathways for the formation of dimer 28. Conditions: KOt-Bu, THF, 1 h, 68% yiel...
Scheme 9: Alkylation of phosphoramidate 13 by iodide 29 to afford compound 30 and byproducts alcohol 31 and d...
NHC-catalyzed enantioselective synthesis of β-trifluoromethyl-β-hydroxyamides
- Alyn T. Davies,
- Mark D. Greenhalgh,
- Alexandra M. Z. Slawin and
- Andrew D. Smith
Beilstein J. Org. Chem. 2020, 16, 1572–1578, doi:10.3762/bjoc.16.129
- ][44][45] in the presence of an oxidant. As representative examples of the use of azolium enolates in reactions with trifluoroacetophenone derivatives, Ye and co-workers have shown that using disubstituted ketenes as azolium enolate precursors and NHC precatalyst 1 allowed access to trifluoromethyl
- enantioselectivity but requiring superstoichiometric quantities of quinone as an oxidant (Figure 2B) [47]. In our previous work, we have developed α-aroyloxyaldehydes as reactive, bench-stable precursors of azolium enolates [48][49][50][51][52][53], which can be synthesized in a single step from the desired aldehyde
Graphical Abstract
Figure 1: Organocatalytic enantioselective aldol approaches using trifluoroacetophenone derivatives.
Figure 2: NHC-catalyzed approaches to β-lactones using trifluoroacetophenone derivatives.
Scheme 1: Reaction scope with respect to the nucleophile. aIsolated yield of the product in >95:5 dr. bDeterm...
Scheme 2: Reaction scope with respect to the trifluoroacetophenone derivative and α-aroyloxyaldehyde. aIsolat...
Scheme 3: Proposed mechanism.
Photocatalyzed syntheses of phenanthrenes and their aza-analogues. A review
- Alessandra Del Tito,
- Havall Othman Abdulla,
- Davide Ravelli,
- Stefano Protti and
- Maurizio Fagnoni
Beilstein J. Org. Chem. 2020, 16, 1476–1488, doi:10.3762/bjoc.16.123
- –C bonds gave P(=O)Ph2-containing phenanthridines 7.5a–c (Scheme 7, path c), which occurred in the presence of a base (CsF or Cs2CO3) and an external oxidant (K2S2O8). Notably, the presence of electron-withdrawing groups on the biphenyl unit inhibited the process in some instances [67]. Starting from
- exploited for the construction of phenanthridine 6-carboxylates (Scheme 12). Notably, the process occurred in water under metal-free conditions in the presence of rose bengal (5 mol %) and made use of molecular oxygen as the terminal oxidant. Thus, N-biarylglycine esters 12.1a–d promoted the reductive
Graphical Abstract
Figure 1: Bioactive phenanthridine and phenanthridinium derivatives.
Scheme 1: Synthesis of phenanthrenes by a photo-Pschorr reaction.
Scheme 2: Synthesis of phenanthrenes by a benzannulation reaction.
Scheme 3: Photocatalytic cyclization of α-bromochalcones for the synthesis of phenanthrenes.
Figure 2: Carbon-centered and nitrogen-centered radicals used for the synthesis of phenanthridines.
Scheme 4: General scheme describing the synthesis of phenanthridines from isocyanides via imidoyl radicals.
Scheme 5: Synthesis of substituted phenanthridines involving the intermediacy of electrophilic radicals.
Scheme 6: Photocatalyzed synthesis of 6-β-ketoalkyl phenanthridines.
Scheme 7: Synthesis of 6-substituted phenanthridines through the addition of trifluoromethyl (path a), phenyl...
Scheme 8: Synthesis of 6-(trifluoromethyl)-7,8-dihydrobenzo[k]phenanthridine.
Scheme 9: Phenanthridine syntheses by using photogenerated radicals formed through a C–H bond homolytic cleav...
Scheme 10: Trifluoroacetimidoyl chlorides as starting substrates for the synthesis of 6-(trifluoromethyl)phena...
Scheme 11: Synthesis of phenanthridines via aryl–aryl-bond formation.
Scheme 12: Oxidative conversion of N-biarylglycine esters to phenanthridine-6-carboxylates.
Scheme 13: Photocatalytic synthesis of benzo[f]quinolines from 2-heteroaryl-substituted anilines and heteroary...
Scheme 14: Synthesis of noravicine (14.2a) and nornitidine (14.2b) alkaloids.
Scheme 15: Gram-scale synthesis of the alkaloid trisphaeridine (15.3).
Scheme 16: Synthesis of phenanthridines starting from vinyl azides.
Scheme 17: Synthesis of pyrido[4,3,2-gh]phenanthridines 17.5a–d through the radical trifluoromethylthiolation ...
Scheme 18: The direct oxidative C–H amidation involving amidyl radicals for the synthesis of phenanthridones.
An overview on disulfide-catalyzed and -cocatalyzed photoreactions
- Yeersen Patehebieke
Beilstein J. Org. Chem. 2020, 16, 1418–1435, doi:10.3762/bjoc.16.118
- electron-rich aryl disulfides as the photocatalyst and oxygen as the oxidant [16]. At room temperature, bis(4-methoxyphenyl) disulfide was employed as the metal-free photocatalyst under visible-light and 1 bar of O2 to realize the aerobic oxidative cleavage of the C=C bonds. Under these mild conditions
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.
Recent synthesis of thietanes
- Jiaxi Xu
Beilstein J. Org. Chem. 2020, 16, 1357–1410, doi:10.3762/bjoc.16.116
Graphical Abstract
Figure 1: Examples of biologically active thietane-containing molecules.
Figure 2: The diverse methods for the synthesis of thietanes.
Scheme 1: Synthesis of 1-(thietan-2-yl)ethan-1-ol (10) from 3,5-dichloropentan-2-ol (9).
Scheme 2: Synthesis of thietanose nucleosides 2,14 from 2,2-bis(bromomethyl)propane-1,3-diol (11).
Scheme 3: Synthesis of methyl 3-vinylthietane-3-carboxylate (19).
Scheme 4: Synthesis of 1,6-thiazaspiro[3.3]heptane (24).
Scheme 5: Synthesis of 6-amino-2-thiaspiro[3.3]heptane hydrochloride (28).
Scheme 6: Synthesis of optically active thietane 31 from vitamin C.
Scheme 7: Synthesis of an optically active thietane nucleoside from diethyl L-tartrate (32).
Scheme 8: Synthesis of thietane-containing spironucleoside 40 from 5-aldo-3-O-benzyl-1,2-O-isopropylidene-α-D...
Scheme 9: Synthesis of optically active 2-methylthietane-containing spironucleoside 43.
Scheme 10: Synthesis of a double-linked thietane-containing spironucleoside 48.
Scheme 11: Synthesis of two diastereomeric thietanose nucleosides via 2,4-di(benzyloxymethyl)thietane (49).
Scheme 12: Synthesis of the thietane-containing PI3k inhibitor candidate 54.
Scheme 13: Synthesis of the spirothietane 57 as the key intermediate to Nuphar sesquiterpene thioalkaloids.
Scheme 14: Synthesis of spirothietane 61 through a direct cyclic thioetherification of 3-mercaptopropan-1-ol.
Scheme 15: Synthesis of thietanes 66 from 1,3-diols 62.
Scheme 16: Synthesis of thietanylbenzimidazolone 75 from (iodomethyl)thiazolobenzimidazole 70.
Scheme 17: Synthesis of 2-oxa-6-thiaspiro[3.3]heptane (80) from bis(chloromethyl)oxetane 76 and thiourea.
Scheme 18: Synthesis of the thietane-containing glycoside, 2-O-p-toluenesulfonyl-4,6-thioanhydro-α-D-gulopyran...
Scheme 19: Synthesis of methyl 4,6-thioanhydro-α-D-glucopyranoside (89).
Scheme 20: Synthesis of thietane-fused α-D-galactopyranoside 93.
Scheme 21: Synthesis of thietane-fused α-D-gulopyranoside 100.
Scheme 22: Synthesis of 3,5-anhydro-3-thiopentofuranosides 104.
Scheme 23: Synthesis of anhydro-thiohexofuranosides 110, 112 and 113 from from 1,2:4,5-di-O-isopropylidene D-f...
Scheme 24: Synthesis of optically active thietanose nucleosides from D- and L-xyloses.
Scheme 25: Synthesis of thietane-fused nucleosides.
Scheme 26: Synthesis of 3,5-anhydro-3-thiopentofuranosides.
Scheme 27: Synthesis of 2-amino-3,5-anhydro-3-thiofuranoside 141.
Scheme 28: Synthesis of thietane-3-ols 145 from (1-chloromethyl)oxiranes 142 and hydrogen sulfide.
Scheme 29: Synthesis of thietane-3-ol 145a from chloromethyloxirane (142a).
Scheme 30: Synthesis of thietane-3-ols 145 from 2-(1-haloalkyl)oxiranes 142 and 147 with ammonium monothiocarb...
Scheme 31: Synthesis of 7-deoxy-5(20)thiapaclitaxel 154a, a thietane derivative of taxoids.
Scheme 32: Synthesis of 5(20)-thiadocetaxel 158 from 10-deacetylbaccatin III (155).
Scheme 33: Synthesis of thietane derivatives 162 as precursors for deoxythiataxoid synthesis through oxiraneme...
Scheme 34: Synthesis of 7-deoxy 5(20)-thiadocetaxel 154b.
Scheme 35: Mechanism for the formation of the thietane ring in 171 from oxiranes with vicinal leaving groups 1...
Scheme 36: Synthesis of cis-2,3-disubstituted thietane 175 from thiirane-2-methanol 172.
Scheme 37: Synthesis of a bridged thietane 183 from aziridine cyclohexyl tosylate 179 and ammonium tetrathiomo...
Scheme 38: Synthesis of thietanes via the photochemical [2 + 2] cycloaddition of thiobenzophenone 184a with va...
Scheme 39: Synthesis of spirothietanes through the photo [2 + 2] cycloaddition of cyclic thiocarbonyls with ol...
Scheme 40: Photochemical synthesis of spirothietane-thioxanthenes 210 from thioxanthenethione (208) and butatr...
Scheme 41: Synthesis of thietanes 213 from 2,4,6-tri(tert-butyl)thiobenzaldehyde (211) with substituted allene...
Scheme 42: Photochemical synthesis of spirothietanes 216 and 217 from N-methylthiophthalimide (214) with olefi...
Scheme 43: Synthesis of fused thietanes from quadricyclane with thiocarbonyl derivatives 219.
Scheme 44: Synthesis of tricyclic thietanes via the photo [2 + 2] cycloaddition of N-methyldithiosuccinimides ...
Scheme 45: Synthesis of tricyclic thietanes via the photo [2 + 2] cycloaddition of N-methylthiosuccinimide/thi...
Scheme 46: Synthesis of tricyclic thietanes via the photo [2 + 2] cycloaddition of N-alkylmonothiophthalimides...
Scheme 47: Synthesis of spirothietanes from dithiosuccinimides 223 with 2,3-dimethyl-2-butene (215a).
Scheme 48: Synthesis of thietanes 248a,b from diaryl thione 184b and ketene acetals 247a,b.
Scheme 49: Photocycloadditions of acridine-9-thiones 249 and pyridine-4(1H)-thione (250) with 2-methylacrynitr...
Scheme 50: Synthesis of thietanes via the photo [2 + 2] cycloaddition of mono-, di-, and trithiobarbiturates 2...
Scheme 51: Synthesis of spirothietanes via the photo [2 + 2] cycloaddition of 1,1,3-trimethyl-2-thioxo-1,2-dih...
Scheme 52: Synthesis of spirothietanes via the photo [2 + 2] cycloaddition of thiocoumarin 286 with olefins.
Scheme 53: Photochemical synthesis of thietanes 296–299 from semicyclic and acyclic thioimides 292–295 and 2,3...
Scheme 54: Photochemical synthesis of spirothietane 301 from 1,3,3-trimethylindoline-2-thione (300) and isobut...
Scheme 55: Synthesis of spirobenzoxazolethietanes 303 via the photo [2 + 2] cycloaddition of alkyl and aryl 2-...
Scheme 56: Synthesis of spirothietanes from tetrahydrothioxoisoquinolines 306 and 307 with olefins.
Scheme 57: Synthesis of spirothietanes from 1,3-dihydroisobenzofuran-1-thiones 311 and benzothiophene-1-thione...
Scheme 58: Synthesis of 2-triphenylsilylthietanes from phenyl triphenylsilyl thioketone (316) with electron-po...
Scheme 59: Diastereoselective synthesis of spiropyrrolidinonethietanes 320 via the photo [2 + 2] cycloaddition...
Scheme 60: Synthesis of bicyclic thietane 323 via the photo [2 + 2] cycloaddition of 2,4-dioxo-3,4-dihydropyri...
Scheme 61: Photo-induced synthesis of fused thietane-2-thiones 325 and 326 from silacyclopentadiene 324 and ca...
Scheme 62: Synthesis of highly strained tricyclic thietanes 328 via the intramolecular photo [2 + 2] cycloaddi...
Scheme 63: Synthesis of tri- and pentacyclic thietanes 330 and 332, respectively, through the intramolecular p...
Scheme 64: Synthesis of tricyclic thietanes 334 via the intramolecular photo [2 + 2] cycloaddition of N-vinylt...
Scheme 65: Synthesis of tricyclic thietanes 336 via the intramolecular photo [2 + 2] cycloaddition of N-but-3-...
Scheme 66: Synthesis of tricyclic thietanes via the intramolecular photo [2 + 2] cycloaddition of N-but-3-enyl...
Scheme 67: Synthesis of tetracyclic thietane 344 through the intramolecular photo [2 + 2] cycloaddition of N-[...
Scheme 68: Synthesis of tri- and tetracyclic thietanes 348, 350, and 351, through the intramolecular photo [2 ...
Scheme 69: Synthesis of tetracyclic fused thietane 354 via the photo [2 + 2] cycloaddition of vinyl 2-thioxo-3H...
Scheme 70: Synthesis of highly rigid thietane-fused β-lactams via the intramolecular photo [2 + 2] cycloadditi...
Scheme 71: Asymmetric synthesis of a highly rigid thietane-fused β-lactam 356a via the intramolecular photo [2...
Scheme 72: Diastereoselective synthesis of the thietane-fused β-lactams via the intramolecular photo [2 + 2] c...
Scheme 73: Asymmetric synthesis of thietane-fused β-lactams 356 via the intramolecular photo [2 + 2] cycloaddi...
Scheme 74: Synthesis of the bridged bis(trifluoromethyl)thietane from 2,2,4,4-tetrakis(trifluoromethyl)-1,3-di...
Scheme 75: Synthesis of the bridged-difluorothietane 368 from 2,2,4,4-tetrafluoro-1,3-dithietane (367) and qua...
Scheme 76: Synthesis of bis(trifluoromethyl)thietanes from 2,2,4,4-tetrakis(trifluoromethyl)-1,3-dithietane (3...
Scheme 77: Synthesis of 2,2-dimethylthio-4,4-di(trifluoromethyl)thietane (378) from 2,2,4,4-tetrakis(trifluoro...
Scheme 78: Formation of bis(trifluoromethyl)thioacetone (381) through nucleophilic attack of dithietane 363 by...
Scheme 79: Synthesis of 2,2-bis(trifluoromethyl)thietanes from 2,2,4,4-tetrakis(trifluoromethyl)-1,3-dithietan...
Scheme 80: Synthesis of the bridged bis(trifluoromethyl)thietane 364 from of 2,2,4,4-tetrakis(trifluoromethyl)...
Scheme 81: Synthesis of 2,4-diiminothietanes 390 from alkenimines and 4-methylbenzenesulfonyl isothiocyanate (...
Scheme 82: Synthesis of arylidene 2,4-diiminothietanes 393 starting from phosphonium ylides 391 and isothiocya...
Scheme 83: Synthesis of thietane-2-ylideneacetates 397 through a DABCO-catalyzed formal [2 + 2] cycloaddition ...
Scheme 84: Synthesis of 3-substituted thietanes 400 from (1-chloroalkyl)thiiranes 398.
Scheme 85: Synthesis of N-(thietane-3-yl)azaheterocycles 403 and 404 through reaction of chloromethylthiirane (...
Scheme 86: Synthesis of 3-sulfonamidothietanes 406 from sulfonamides and chloromethylthiirane (398a).
Scheme 87: Synthesis of N-(thietane-3-yl)isatins 408 from chloromethylthiirane (398a) and isatins 407.
Scheme 88: Synthesis of 3-(nitrophenyloxy)thietanes 410 from nitrophenols 409 and chloromethylthiirane (398a).
Scheme 89: Synthesis of N-aryl-N-(thietane-3-yl)cyanamides 412 from N-arylcyanamides 411 and chloromethylthiir...
Scheme 90: Synthesis of 1-(thietane-3-yl)pyrimidin-2,4(1H,3H)-diones 414 from chloromethylthiirane (398a) and ...
Scheme 91: Synthesis of 2,4-diiminothietanes 418 from 2-iminothiiranes 416 and isocyanoalkanes 415.
Scheme 92: Synthesis of 2-vinylthietanes 421 from thiiranes 419 and 3-chloroallyl lithium (420).
Scheme 93: Synthesis of thietanes from thiiranes 419 and trimethyloxosulfonium iodide 424.
Scheme 94: Mechanism for synthesis of thietanes 425 from thiiranes 419 and trimethyloxosulfonium iodide 424.
Scheme 95: Synthesis of functionalized thietanes from thiiranes and dimethylsulfonium acylmethylides.
Scheme 96: Mechanism for the rhodium-catalyzed synthesis of functionalized thietanes 429 from thiiranes 419 an...
Scheme 97: Synthesis of 3-iminothietanes 440 through thermal isomerization from 4,5-dihydro-1,3-oxazole-4-spir...
Scheme 98: Synthesis of thietanes 443 from 3-chloro-2-methylthiolane (441) through ring contraction.
Scheme 99: Synthesis of an optically active thietanose 447 from D-xylose involving a ring contraction.
Scheme 100: Synthesis of optically thietane 447 via the DAST-mediated ring contraction of 448.
Scheme 101: Synthesis of the optically thietane nucleoside 451 via the ring contraction of thiopentose in 450.
Scheme 102: Synthesis of spirothietane 456 from 3,3,5,5-tetramethylthiolane-2,4-dithione (452) and benzyne (453...
Scheme 103: Synthesis of thietanes 461 via photoisomerization of 2H,6H-thiin-3-ones 459.
Scheme 104: Phosphorodithioate-mediated synthesis of 1,4-diarylthietanes 465.
Scheme 105: Mechanism of the phosphorodithioate-mediated synthesis of 1,4-diarylthietanes 465.
Scheme 106: Phosphorodithioate-mediated synthesis of trisubstituted thietanes (±)-470.
Scheme 107: Mechanism on the phosphorodithioate-mediated synthesis of trisubstituted thietanes.
Scheme 108: Phosphorodithioate-mediated synthesis of thietanes (±)-475.
Scheme 109: Phosphorodithioate-mediated synthesis of 1,2-disubstituted thietanes from aldehydes 476 and acrylon...
Scheme 110: Phosphorodithioate-mediated synthesis of 1,2-disubstituted thietanes via a one-pot three-component ...
Scheme 111: Mechanism for the phosphorodithioate-mediated synthesis of 1,2-disubstituted thietanes via three-co...
Scheme 112: Phosphorodithioate-mediated synthesis of substituted 3-nitrothietanes.
Scheme 113: Mechanism on the phosphorodithioate-mediated synthesis of 1,2-disubstituted thietanes (±)-486.
Scheme 114: Asymmetric synthesis of (S)-2-phenylthietane (497).
Scheme 115: Asymmetric synthesis of optically active 2,4-diarylthietanes.
Scheme 116: Synthesis of 3-acetamidothietan-2-one 503 via the intramolecular thioesterification of 3-mercaptoal...
Scheme 117: Synthesis of 4-substituted thietan-2-one via the intramolecular thioesterification of 3-mercaptoalk...
Scheme 118: Synthesis of 4,4-disubstituted thietan-2-one 511 via the intramolecular thioesterification of the 3...
Scheme 119: Synthesis of a spirothietan-2-one 514 via the intramolecular thioesterification of 3-mercaptoalkano...
Scheme 120: Synthesis of thiatetrahydrolipstatin starting from (S)-(−)-epichlorohydrin ((S)-142a).
Scheme 121: Synthesis of 2-phenethyl-4-(propan-2-ylidene)thietane (520) from 5-bromo-6-methyl-1-phenylhept-5-en...
Scheme 122: Synthesis of 2-phenethyl-4-(propan-2-ylidene)thietane (520) directly from S-(5-bromo-6-methyl-1-phe...
Scheme 123: Synthesis of 2-alkylidenethietanes from S-(2-bromoalk-1-en-4-yl)thioacetates.
Scheme 124: Synthesis of 2-alkylidenethietanes from S-(2-bromo/chloroalk-1-en-4-yl)thiols.
Scheme 125: Synthesis of spirothietan-3-ol 548 from enone 545 and ammonium hydrosulfide.
Scheme 126: Asymmetric synthesis of the optically active thietanoside from cis-but-2-ene-1,4-diol (47).
Scheme 127: Synthesis of 2-alkylidenethietan-3-ols 557 via the fluoride-mediated cyclization of thioacylsilanes ...
Scheme 128: Synthesis of 2-iminothietanes via the reaction of propargylbenzene (558) and isothiocyanates 560 in...
Scheme 129: Synthesis of 2-benzylidenethietane 567 via the nickel complex-catalyzed electroreductive cyclizatio...
Scheme 130: Synthesis of 2-iminothietanes 569 via the photo-assisted electrocyclic reaction of N-monosubstitute...
Scheme 131: Synthesis of ethyl 3,4-diiminothietane-2-carboxylates from ethyl thioglycolate (570) and bis(imidoy...
Scheme 132: Synthesis of N-(thietan-3-yl)-α-oxoazaheterocycles from azaheterocyclethiones and chloromethyloxira...
Scheme 133: Synthesis of thietan-3-yl benzoate (590) via the nickel-catalyzed intramolecular reductive thiolati...
Scheme 134: Synthesis of 2,2-bis(trifluoromethyl)thietane from 3,3-bis(trifluoromethyl)-1,2-dithiolane.
Scheme 135: Synthesis of thietanes from enamines and sulfonyl chlorides.
Scheme 136: Synthesis of spirothietane 603 via the [2 + 3] cycloaddition of 2,2,4,4-tetramethylcyclobutane-1,3-...
Scheme 137: Synthesis of thietane (605) from 1-bromo-3-chloropropane and sulfur.
Highly selective Diels–Alder and Heck arylation reactions in a divergent synthesis of isoindolo- and pyrrolo-fused polycyclic indoles from 2-formylpyrrole
- Carlos H. Escalante,
- Eder I. Martínez-Mora,
- Carlos Espinoza-Hicks,
- Alejandro A. Camacho-Dávila,
- Fernando R. Ramos-Morales,
- Francisco Delgado and
- Joaquín Tamariz
Beilstein J. Org. Chem. 2020, 16, 1320–1334, doi:10.3762/bjoc.16.113
- electronic density provided by the nitrogen lone-pair, which plausibly stabilizes the cationic or radical species formed by the oxidant reagent during the aromatization process [46], as efficiently occurred with derivatives 9. Finally, in order to obtain the aromatic indole-based pentacycles 12, the
Graphical Abstract
Figure 1: Fused aza-hetero polycyclic frames and natural pyrrolizine- and isoindole-containing alkaloids.
Scheme 1: Synthetic approaches for the preparation of pyrrolo-fused aza-hetero polycyclic frames.
Scheme 2: Preparation of 1,2-substituted pyrroles 8a–f and 8i,j.
Scheme 3: Diels–Alder cycloadditions of pyrroles 8a–j and 16a–b with maleimides 7b–c.
Figure 2: Structures of 9m (a) and 10m (b) as determined by single-crystal X-ray diffraction crystallography ...
Scheme 4: Pd(0)-catalyzed intramolecular Heck cross-coupling reaction of 2-vinylpyrroles 8c,d and 8g.
Scheme 5: Synthesis of 2-vinylpyrroles 8k,l and their Pd(0)-catalyzed intramolecular Heck cross-coupling to p...
Scheme 6: Diastereoselective Diels–Alder reaction of pyrrolo[2,1-a]isoindole 18a with 7c.
Scheme 7: Synthetic approach to the fused aza-heterocyclic pentacycle 12.
Figure 3: M06-2X/6-31+G(d,p) Optimized geometry for each of the SCs (a and d), TSs (b and e) and ADs (c and f...
Figure 4: M06-2X/6-31+G(d,p) Optimized geometry for each of the TSs of the Diels–Alder reactions of dienes 8b...
Figure 5: M06-2X/6-31+G(d,p) Optimized geometry of the endo SCs (a) and TSs (b) for the Diels–Alder reaction ...
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
- strong single-electron oxidant, cerium(IV) ammonium nitrate, in methanol [38]. To record EPR spectra, a flow system was used, which allowed observation of radicals with lifetimes of about 10−2 s [39]. The EPR spectra of iminoxyl radicals are characterized by large values of the hyperfine splitting
- optimization of the reaction conditions Fe(ClO4)3 was chosen as the optimal oxidant for the synthesis of C–O cross-dehydrogenative coupling products 51 (Scheme 19). The extremely persistent diacetyliminoxyl radical (20) [44] was directly introduced into the reaction with pyrazolones 50 with the formation of
- using DTBP or aerial oxygen as an oxidant. Aliphatic, aromatic, and heteroaromatic amines 140, both primary and secondary, are applicable for this reaction. The reaction of TEMPO with β,γ- and γ,δ-unsaturated oximes 143 leads to substituted unsaturated isoxazolines 144 and cyclic nitrones 145
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.
Photocatalysis with organic dyes: facile access to reactive intermediates for synthesis
- Stephanie G. E. Amos,
- Marion Garreau,
- Luca Buzzetti and
- Jerome Waser
Beilstein J. Org. Chem. 2020, 16, 1163–1187, doi:10.3762/bjoc.16.103
- quenching cycle, PC* acts as a reductant donating an electron to A. This generates the oxidized form of the photocatalyst, PC•+, and a reduced acceptor, A•−. Alternatively, in a reductive quenching cycle, PC* acts as an oxidant promoting an SET oxidation of the electron donor D. This leads to the reduced
- use of the strong oxidant Mes-Acr-Ph+ (OD3, E(PC+*/PC) ≈ 2 V) as organic photocatalyst leads to the oxidation/decarboxylation of the in situ-generated carboxylates (Eox ≈ 1.3 V). An organic disulfide cocatalyst, (PhS)2, activated by the reduced photocatalyst, was found to act as a co-base (PhS−) and a
- cyclic ethers 22.3. Mes-Acr-Me+ (OD2) is a strong enough oxidant (E(PC+*/PC) ≈ 2.1 V), allowing the oxidation of unactivated alkenes (1.2 ≤ Eox ≤ 1.9 V). In this transformation, the cocatalyst 22.2 acts as an H atom shuttle. This alkene radical cation-based strategy has been extended to various
Graphical Abstract
Figure 1: Selected examples of organic dyes. Mes-Acr+: 9-mesityl-10-methylacridinium, DCA: 9,10-dicyanoanthra...
Scheme 1: Activation modes in photocatalysis.
Scheme 2: Main strategies for the formation of C(sp3) radicals used in organophotocatalysis.
Scheme 3: Illustrative example for the photocatalytic oxidative generation of radicals from carboxylic acids:...
Scheme 4: Illustrative example for the photocatalytic reductive generation of C(sp3) radicals from redoxactiv...
Figure 2: Common substrates for the photocatalytic oxidative generation of C(sp3) radicals.
Scheme 5: Illustrative example for the photocatalytic oxidative generation of radicals from dihydropyridines ...
Scheme 6: Illustrative example for the photocatalytic oxidative generation of C(sp3) radicals from trifluorob...
Scheme 7: Illustrative example for the photocatalytic reductive generation of C(sp3) radicals from benzylic h...
Scheme 8: Illustrative example for the photocatalytic generation of C(sp3) radicals via direct HAT: the cross...
Scheme 9: Illustrative example for the photocatalytic generation of C(sp3) radicals via indirect HAT: the deu...
Scheme 10: Selected precursors for the generation of aryl radicals using organophotocatalysis.
Scheme 11: Illustrative example for the photocatalytic reductive generation of aryl radicals from aryl diazoni...
Scheme 12: Illustrative examples for the photocatalytic reductive generation of aryl radicals from haloarenes:...
Scheme 13: Illustrative example for the photocatalytic reductive generation of aryl radicals from aryl halides...
Scheme 14: Illustrative example for the photocatalytic reductive generation of aryl radicals from arylsulfonyl...
Scheme 15: Illustrative example for the reductive photocatalytic generation of aryl radicals from triaryl sulf...
Scheme 16: Main strategies towards acyl radicals used in organophotocatalysis.
Scheme 17: Illustrative example for the decarboxylative photocatalytic generation of acyl radicals from α-keto...
Scheme 18: Illustrative example for the oxidative photocatalytic generation of acyl radicals from acyl silanes...
Scheme 19: Illustrative example for the oxidative photocatalytic generation of carbamoyl radicals from 4-carba...
Scheme 20: Illustrative example of the photocatalytic HAT approach for the generation of acyl radicals from al...
Scheme 21: General reactivity of a) radical cations; b) radical anions; c) the main strategies towards aryl an...
Scheme 22: Illustrative example for the oxidative photocatalytic generation of alkene radical cations from alk...
Scheme 23: Illustrative example for the reductive photocatalytic generation of an alkene radical anion from al...
Figure 3: Structure of C–X radical anions and their neutral derivatives.
Scheme 24: Illustrative example for the photocatalytic reduction of imines and the generation of an α-amino C(...
Scheme 25: Illustrative example for the oxidative photocatalytic generation of aryl radical cations from arene...
Scheme 26: NCR classifications and generation.
Scheme 27: Illustrative example for the photocatalytic reductive generation of iminyl radicals from O-aryl oxi...
Scheme 28: Illustrative example for the photocatalytic oxidative generation of iminyl radicals from α-N-oxy ac...
Scheme 29: Illustrative example for the photocatalytic oxidative generation of iminyl radicals via an N–H bond...
Scheme 30: Illustrative example for the photocatalytic oxidative generation of amidyl radicals from Weinreb am...
Scheme 31: Illustrative example for the photocatalytic reductive generation of amidyl radicals from hydroxylam...
Scheme 32: Illustrative example for the photocatalytic reductive generation of amidyl radicals from N-aminopyr...
Scheme 33: Illustrative example for the photocatalytic oxidative generation of amidyl radicals from α-amido-ox...
Scheme 34: Illustrative example for the photocatalytic oxidative generation of aminium radicals: the N-aryltet...
Scheme 35: Illustrative example for the photocatalytic oxidative generation of nitrogen-centered radical catio...
Scheme 36: Illustrative example for the photocatalytic oxidative generation of nitrogen-centered radical catio...
Scheme 37: Illustrative example for the photocatalytic oxidative generation of hydrazonyl radical from hydrazo...
Scheme 38: Generation of O-radicals.
Scheme 39: Illustrative examples for the photocatalytic generation of O-radicals from N-alkoxypyridinium salts...
Scheme 40: Illustrative examples for the photocatalytic generation of O-radicals from alkyl hydroperoxides: th...
Scheme 41: Illustrative example for the oxidative photocatalytic generation of thiyl radicals from thiols: the...
Scheme 42: Main strategies and reagents for the generation of sulfonyl radicals used in organophotocatalysis.
Scheme 43: Illustrative example for the reductive photocatalytic generation of sulfonyl radicals from arylsulf...
Scheme 44: Illustrative example of a Cl atom abstraction strategy for the photocatalytic generation of sulfamo...
Scheme 45: Illustrative example for the oxidative photocatalytic generation of sulfonyl radicals from sulfinic...
Scheme 46: Illustrative example for the photocatalytic generation of electronically excited triplet states: th...
Scheme 47: Illustrative example for the photocatalytic generation of electronically excited triplet states: th...
Synthesis and anticancer activity of bis(2-arylimidazo[1,2-a]pyridin-3-yl) selenides and diselenides: the copper-catalyzed tandem C–H selenation of 2-arylimidazo[1,2-a]pyridine with selenium
- Mio Matsumura,
- Tsutomu Takahashi,
- Hikari Yamauchi,
- Shunsuke Sakuma,
- Yukako Hayashi,
- Tadashi Hyodo,
- Tohru Obata,
- Kentaro Yamaguchi,
- Yasuyuki Fujiwara and
- Shuji Yasuike
Beilstein J. Org. Chem. 2020, 16, 1075–1083, doi:10.3762/bjoc.16.94
- oxidant) as the selenium source under acidic conditions, and the substrate scope and limitations have not been clarified. Moreover, the syntheses of bis(2-arylimidazo[1,5-a]pyridin-3-yl) selenides and diselenides have recently been investigated using Cu-catalyzed reactions involving imidazo[1,5-a
Graphical Abstract
Figure 1: Biologically active selenides and diselenides having heteroaryl groups.
Figure 2: Ortep drawings of 2a (a and b) and 3a (c and d, thermal elipsoids indicate 50% probability).
Figure 3: The synthesis of bis(2-arylimidazopyridin-3-yl) diselenides. Reaction conditions: 1 (2 mmol), Se (2...
Figure 4: The synthesis of bis(2-arylimidazopyridin-3-yl) selenides. Reaction conditions: 1 (2 mmol), Se (1 m...
Scheme 1: Control reactions.
Scheme 2: Proposed mechanism (1).
Scheme 3: Proposed mechanism (2).
Figure 5: The cytotoxic effect of the bis(2-arylimidazo[1,2-a]pyridin-3-yl) diselenides 2 and selenides 3 on ...
Figure 6: The cytotoxic effect of the bis[2-(4-methoxyphenyl)imidazo[1,2-a]pyridin-3-yl] diselenide 2f on can...
Figure 7: Cytotoxic effect of the bis[2-(4-methoxyphenyl)imidazo[1,2-a]pyridin-3-yl] diselenide 2f on a cance...
Recent applications of porphyrins as photocatalysts in organic synthesis: batch and continuous flow approaches
- Rodrigo Costa e Silva,
- Luely Oliveira da Silva,
- Aloisio de Andrade Bartolomeu,
- Timothy John Brocksom and
- Kleber Thiago de Oliveira
Beilstein J. Org. Chem. 2020, 16, 917–955, doi:10.3762/bjoc.16.83
- application in the synthesis of quinazolin-4-(3H)-ones by the one-pot reaction between alcohols and 2-aminobenzamide under an oxidative quenching, visible light irradiation using air or oxygen as oxidant (60–81% yields). The authors propose the generation of the superoxide radical anion with the MOF. The
Graphical Abstract
Figure 1: Chemical structures of the porphyrinoids and their absorption spectra: in bold are highlighted the ...
Figure 2: Photophysical and photochemical processes (Por = porphyrin). Adapted from [12,18].
Figure 3: Main dual photocatalysts and their oxidative/reductive excited state potentials, including porphyri...
Scheme 1: Photoredox alkylation of aldehydes with diazo acetates using porphyrins and a Ru complex. aUsing a ...
Scheme 2: Proposed mechanism for the alkylation of aldehydes with diazo acetates in the presence of TPP.
Scheme 3: Arylation of heteroarenes with aryldiazonium salts using TPFPP as photocatalyst, and corresponding ...
Scheme 4: A) Scope with different aryldiazonium salts and enol acetates. B) Photocatalytic cycles and compari...
Scheme 5: Photoarylation of isopropenyl acetate A) Comparison between batch and continuous-flow approaches an...
Scheme 6: Dehalogenation induced by red light using thiaporphyrin (STPP).
Scheme 7: Applications of NiTPP as both photoreductant and photooxidant.
Scheme 8: Proposed mechanism for obtaining tetrahydroquinolines by reductive quenching.
Scheme 9: Selenylation and thiolation of anilines.
Scheme 10: NiTPP as photoredox catalyst in oxidative and reductive quenching, in comparison with other photoca...
Scheme 11: C–O bond cleavage of 1-phenylethanol using a cobalt porphyrin (CoTMPP) under visible light.
Scheme 12: Hydration of terminal alkynes by RhIII(TSPP) under visible light irradiation.
Scheme 13: Regioselective photocatalytic hydro-defluorination of perfluoroarenes by RhIII(TSPP).
Scheme 14: Formation of 2-methyl-2,3-dihydrobenzofuran by intramolecular hydro-functionalization of allylpheno...
Scheme 15: Photocatalytic oxidative hydroxylation of arylboronic acids using UNLPF-12 as heterogeneous photoca...
Scheme 16: Photocatalytic oxidative hydroxylation of arylboronic acids using MOF-525 as heterogeneous photocat...
Scheme 17: Preparation of the heterogeneous photocatalyst CNH.
Scheme 18: Photoinduced sulfonation of alkenes with sulfinic acid using CNH as photocatalyst.
Scheme 19: Sulfonic acid scope of the sulfonation reactions.
Scheme 20: Regioselective sulfonation reaction of arimistane.
Scheme 21: Synthesis of quinazolin-4-(3H)-ones.
Scheme 22: Selective photooxidation of aromatic benzyl alcohols to benzaldehydes using Pt/PCN-224(Zn).
Scheme 23: Photooxidation of benzaldehydes to benzoic acids using Pt or Pd porphyrins.
Scheme 24: Photocatalytic reduction of various nitroaromatics using a Ni-MOF.
Scheme 25: Photoinduced cycloadditions of CO2 with epoxides by MOF1.
Figure 4: Electronic configurations of the species of oxygen. Adapted from [66].
Scheme 26: TPP-photocatalyzed generation of 1O2 and its application in organic synthesis. Adapted from [67-69].
Scheme 27: Pericyclic reactions involving singlet oxygen and their mechanisms. Adapted from [67].
Scheme 28: First scaled up ascaridole preparation from α-terpinene.
Scheme 29: Antimalarial drug synthesis using an endoperoxidation approach.
Scheme 30: Photooxygenation of colchicine.
Scheme 31: Synthesis of (−)-pinocarvone from abundant (+)-α-pinene.
Scheme 32: Seeberger’s semi-synthesis of artemisinin.
Scheme 33: Synthesis of artemisinin using TPP and supercritical CO2.
Scheme 34: Synthesis of artemisinin using chlorophyll a.
Scheme 35: Quercitol stereoisomer preparation.
Scheme 36: Photocatalyzed preparation of naphthoquinones.
Scheme 37: Continuous endoperoxidation of conjugated dienes and subsequent rearrangements leading to oxidized ...
Scheme 38: The Opatz group total synthesis of (–)-oxycodone.
Scheme 39: Biomimetic syntheses of rhodonoids A, B, E, and F.
Scheme 40: α-Photooxygenation of chiral aldehydes.
Scheme 41: Asymmetric photooxidation of indanone β-keto esters by singlet oxygen using PTC as a chiral inducer...
Scheme 42: Asymmetric photooxidation of both β-keto esters and β-keto amides by singlet oxygen using PTC-2 as ...
Scheme 43: Bifunctional photo-organocatalyst used for the asymmetric oxidation of β-keto esters and β-keto ami...
Scheme 44: Mechanism of singlet oxygen oxidation of sulfides to sulfoxides.
Scheme 45: Controlled oxidation of sulfides to sulfoxides using protonated porphyrins as photocatalysts. aIsol...
Scheme 46: Photochemical oxidation of sulfides to sulfoxides using PdTPFPP as photocatalyst.
Scheme 47: Controlled oxidation of sulfides to sulfoxides using SnPor@PAF as a photosensitizer.
Scheme 48: Syntheses of 2D-PdPor-COF and 3D-Pd-COF.
Scheme 49: Photocatalytic oxidation of A) thioanisole to methyl phenyl sulfoxide and B) various aryl sulfides,...
Scheme 50: General mechanism for oxidation of amines to imines.
Scheme 51: Oxidation of secondary amines to imines.
Scheme 52: Oxidation of secondary amines using Pd-TPFPP as photocatalyst.
Scheme 53: Oxidative amine coupling using UNLPF-12 as heterogeneous photocatalyst.
Scheme 54: Synthesis of Por-COF-1 and Por-COF-2.
Scheme 55: Photocatalytic oxidation of amines to imines by Por-COF-2.
Scheme 56: Photocyanation of primary amines.
Scheme 57: Synthesis of ᴅ,ʟ-tert-leucine hydrochloride.
Scheme 58: Photocyanation of catharanthine and 16-O-acetylvindoline using TPP.
Scheme 59: Photochemical α-functionalization of N-aryltetrahydroisoquinolines using Pd-TPFPP as photocatalyst.
Scheme 60: Ugi-type reaction with 1,2,3,4-tetrahydroisoquinoline using molecular oxygen and TPP.
Scheme 61: Ugi-type reaction with dibenzylamines using molecular oxygen and TPP.
Scheme 62: Mannich-type reaction of tertiary amines using PdTPFPP as photocatalyst.
Scheme 63: Oxidative Mannich reaction using UNLPF-12 as heterogeneous photocatalyst.
Scheme 64: Transformation of amines to α-cyanoepoxides and the proposed mechanism.
Bipyrrole boomerangs via Pd-mediated tandem cyclization–oxygenation. Controlling reaction selectivity and electronic properties
- Liliia Moshniaha,
- Marika Żyła-Karwowska,
- Joanna Cybińska,
- Piotr J. Chmielewski,
- Ludovic Favereau and
- Marcin Stępień
Beilstein J. Org. Chem. 2020, 16, 895–903, doi:10.3762/bjoc.16.81
- stoichiometric oxidant. The scope of such Pd(II)-induced couplings was further developed into tandem processes involving consecutive cyclization of substituents (dcTTEE) and oxygenation of pyrrolic α-positions to form lactams cNDA1O and cNMI1O. The mechanism of those transformations was subsequently explored
Graphical Abstract
Scheme 1: The previously reported family of the boomerang bipyrroles obtained by Pd-induced double C–H bond a...
Scheme 2: Synthesis and structures of α-free and α-oxygenated bipyrrole boomerangs. Reagents and conditions: ...
Figure 1: DFT-Optimized structures (B3LYP/6-31G(d,p)) of cNDA2O and cNMI3H.
Figure 2: Absorption and emission spectra of cNMI2H (top) and cNMI3H (bottom) measured in toluene, dichlorome...
Photocatalytic deaminative benzylation and alkylation of tetrahydroisoquinolines with N-alkylpyrydinium salts
- David Schönbauer,
- Carlo Sambiagio,
- Timothy Noël and
- Michael Schnürch
Beilstein J. Org. Chem. 2020, 16, 809–817, doi:10.3762/bjoc.16.74
- ], alkynation [17][18], or allylation [19]), this method has certain drawbacks, most importantly the frequent requirement of superstoichiometric amounts of an oxidant. Hence, alternative methods were investigated and photoredox catalysis proved to be a viable option [20][21][22]. By now, several different
Graphical Abstract
Scheme 1: Examples of photocatalytic C–C bond formation by nucleophilic trapping of a reactive THIQ intermedi...
Figure 1: Kinetic profile for the benzylation of 1 to 3.
Scheme 2: Benzylation of N-phenyl-THIQ.
Scheme 3: Benzylation of substituted N-arylTHIQs.
Scheme 4: Removal of the PMP protecting group.
Scheme 5: Alkylation of N-phenyl-THIQ derivatives. Conditions: a2 mol % [Ir(dtbbpy)(ppy)2]PF6, DMA, 60 h; b2 ...
Scheme 6: Proposed mechanism.
Direct borylation of terrylene and quaterrylene
- Haruka Kano,
- Keiji Uehara,
- Kyohei Matsuo,
- Hironobu Hayashi,
- Hiroko Yamada and
- Naoki Aratani
Beilstein J. Org. Chem. 2020, 16, 621–627, doi:10.3762/bjoc.16.58
- with AlCl3 reproducibly provided a pure terrylene [8]. Scholl reaction using a superacid catalyst in combination with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as oxidant provides a scalable preparation of quaterrylene [9], but unfortunately the low solubility prevents 1H NMR characterization
Graphical Abstract
Figure 1: Chemical structures of a) oligorylene-bisimides, b) oligorylenes, c) bay-bridging oligorylenes, d) ...
Scheme 1: Synthesis of 2,5,10,13-tetrakis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)terrylene (TB4): (a) (B...
Figure 2: (Top) Single crystal X-ray structure of TB4. The thermal ellipsoids are scaled at 50% probability. ...
Figure 3: UV–vis absorption and fluorescence spectra of terrylene (black) and TB4 (red) in toluene. λex = 489...
Figure 4: MO diagrams of terrylene and TB4 based on calculations at the B3LYP/6-31G(d).
Scheme 2: Synthesis of 2,5,12,15-tetrakis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)quaterrylene (QB4): (a)...
Figure 5: UV–vis absorption spectrum of QB4 in toluene.
Figure 6: MO diagrams of terrylene and QB4 based on calculations at the B3LYP/6-31G(d).
Scheme 3: Suzuki–Miyaura cross-coupling reaction of TB4 with 2-bromomesitylene. (a) 2-bromomesitylene (8 equi...
KOt-Bu-promoted selective ring-opening N-alkylation of 2-oxazolines to access 2-aminoethyl acetates and N-substituted thiazolidinones
- Qiao Lin,
- Shiling Zhang and
- Bin Li
Beilstein J. Org. Chem. 2020, 16, 492–501, doi:10.3762/bjoc.16.44
- synthesis of β-nitrate ester carboxamides using tert-butyl nitrite as the nitro source and oxygen as the oxidant through the ring opening of 2-oxazolines [9] (Scheme 1a). Kappe reported a two-step continuous-flow synthesis of N-(2-aminoethyl)acylamides through ring opening/hydrogenation of oxazolines with
Graphical Abstract
Scheme 1: Comparison of different ring-opening reactions of 2-oxazolines and thiazolidinones synthesis.
Scheme 2: KOt-Bu-promoted selective ring-opening N-alkylation of 2-methyl-2-oxazoline with benzyl bromides. C...
Scheme 3: KOt-Bu-promoted selective ring-opening N-alkylation of 2-methyl-2-oxazoline with benzyl chlorides. ...
Scheme 4: KOt-Bu-promoted selective ring-opening N-alkylation of 2,4,4-trimethyl-4,5-dihydrooxazole (2b) with...
Scheme 5: KOt-Bu/I2-promoted selective N-alkylation to synthesis of thiazolidone derivatives. Conditions: KOt...
Scheme 6: Transformation of 2-aminoethyl acetate derivative to 2-(dibenzylamino)ethanol.
Scheme 7: Control experiments and 18O-labeling experiment.
Scheme 8: Control experiments with radical scavengers.
Scheme 9: Proposed mechanism.
Recent advances in photocatalyzed reactions using well-defined copper(I) complexes
- Mingbing Zhong,
- Xavier Pannecoucke,
- Philippe Jubault and
- Thomas Poisson
Beilstein J. Org. Chem. 2020, 16, 451–481, doi:10.3762/bjoc.16.42
- 2012, Collins and co-workers described a copper-catalyzed photocyclization to synthesize [5]helicene (Scheme 29) [43]. Using the in situ-formed [Cu(I)(dmp)(xantphos)]BF4 (25 mol %) in the presence of iodine and propylene oxide as the oxidant system under visible light irradiation, [5]helicene was
Graphical Abstract
Scheme 1: [Cu(I)(dap)2]Cl-catalyzed ATRA reaction under green light irradiation.
Scheme 2: Photocatalytic allylation of α-haloketones.
Scheme 3: [Cu(I)(dap)2]Cl-photocatalyzed chlorosulfonylation and chlorotrifluoromethylation of alkenes.
Scheme 4: Photocatalytic perfluoroalkylchlorination of electron-deficient alkenes using the Sauvage catalyst.
Scheme 5: Photocatalytic synthesis of fluorinated sultones.
Scheme 6: Photocatalyzed haloperfluoroalkylation of alkenes and alkynes.
Scheme 7: Chlorosulfonylation of alkenes catalyzed by [Cu(I)(dap)2]Cl. aNo Na2CO3 was added. b1 equiv of Na2CO...
Scheme 8: Copper-photocatalyzed reductive allylation of diaryliodonium salts.
Scheme 9: Copper-photocatalyzed azidomethoxylation of olefins.
Scheme 10: Benzylic azidation initiated by [Cu(I)(dap)2]Cl.
Scheme 11: Trifluoromethyl methoxylation of styryl derivatives using [Cu(I)(dap)2]PF6. All redox potentials ar...
Scheme 12: Trifluoromethylation of silyl enol ethers.
Scheme 13: Synthesis of annulated heterocycles upon oxidation with the Sauvage catalyst.
Scheme 14: Oxoazidation of styrene derivatives using [Cu(dap)2]Cl as a precatalyst.
Scheme 15: [Cu(I)(dpp)(binc)]PF6-catalyzed ATRA reaction.
Scheme 16: Allylation reaction of α-bromomalonate catalyzed by [Cu(I)(dpp)(binc)]PF6 following an ATRA mechani...
Scheme 17: Bromo/tribromomethylation reaction using [Cu(I)(dmp)(BINAP)]PF6.
Scheme 18: Chlorotrifluoromethylation of alkenes catalyzed by [Cu(I)(N^N)(xantphos)]PF6.
Scheme 19: Chlorosulfonylation of styrene and alkyne derivatives by ATRA reactions.
Scheme 20: Reduction of aryl and alkyl halides with the complex [Cu(I)(bcp)(DPEPhos)]PF6. aIrradiation was car...
Scheme 21: Meerwein arylation of electron-rich aromatic derivatives and 5-exo-trig cyclization catalyzed by th...
Scheme 22: [Cu(I)(bcp)(DPEPhos)]PF6-photocatalyzed synthesis of alkaloids. aYield over two steps (cyclization ...
Scheme 23: Copper-photocatalyzed decarboxylative amination of NHP esters.
Scheme 24: Photocatalytic decarboxylative alkynylation using [Cu(I)(dq)(binap)]BF4.
Scheme 25: Copper-photocatalyzed alkylation of glycine esters.
Scheme 26: Copper-photocatalyzed borylation of organic halides. aUnder continuous flow conditions.
Scheme 27: Copper-photocatalyzed α-functionalization of alcohols with glycine ester derivatives.
Scheme 28: δ-Functionalization of alcohols using [Cu(I)(dmp)(xantphos)]BF4.
Scheme 29: Photocatalytic synthesis of [5]helicene and phenanthrene.
Scheme 30: Oxidative carbazole synthesis using in situ-formed [Cu(I)(dmp)(xantphos)]BF4.
Scheme 31: Copper-photocatalyzed functionalization of N-aryl tetrahydroisoquinolines.
Scheme 32: Bicyclic lactone synthesis using a copper-photocatalyzed PCET reaction.
Scheme 33: Photocatalytic Pinacol coupling reaction catalyzed by [Cu(I)(pypzs)(BINAP)]BF4. The ligands of the ...
Scheme 34: Azide photosensitization using a Cu-based photocatalyst.
Visible-light-induced addition of carboxymethanide to styrene from monochloroacetic acid
- Kaj M. van Vliet,
- Nicole S. van Leeuwen,
- Albert M. Brouwer and
- Bas de Bruin
Beilstein J. Org. Chem. 2020, 16, 398–408, doi:10.3762/bjoc.16.38
- by the work of Yoon, Stephenson and MacMillan [11]. By selective excitation of an organic or organometallic dye by visible light a species is formed that can act as a single-electron oxidant and single-electron reductant. In this way reactive radical intermediates can be formed catalytically in situ
- , resulting in reactivity different from common two-electron pathways. Photoredox catalysis reactivity is very different from traditional redox reactions, and the same reactivity cannot be achieved by stoichiometric addition of both a reductant and an oxidant to a reaction mixture (as that would lead to a
- rapid redox reaction between the oxidant and the reducing agent instead of converting the substrate). Excitation of the photocatalyst, on the other hand, allows continuous formation of low concentrations of both oxidized and reduced radical forms of the substrate(s), and the excited catalysts (and/or
Graphical Abstract
Figure 1: A part of the industry around monochloroacetic acid.
Scheme 1: Redox based activation of haloacetic acid.
Figure 2: Cyclic voltammogram of monochloroacetic acid and ferrocene with 0.1 M [TBA][PF6] in MeCN. The poten...
Scheme 2: Initial attempts for lactone formation by photoredox catalysis.
Scheme 3: The photoredox reaction of TEMPO with monochloroacetic acid catalyzed by fac-[Ir(ppy)3].
Figure 3: EPR spectra measured (black) and simulated (red) based on the structure of the oxidized photoredox ...
Scheme 4: Two possible acid-assisted, reductive activation pathways of monochloroacetic acid (A–H = acid).
Figure 4: Reaction mixtures after overnight irradiation of (A) 4-chloro-4-phenylbutanoic acid (3) and fac-[Ir...
Scheme 5: Substrate scope of styrene derivatives in the photoredox reaction with monochloroacetic acid. Yield...
Scheme 6: Proposed reaction mechanism.
Scheme 7: The photoredox formation of 1-(chloromethoxy)-2,2,6,6-tetramethylpiperidine.
Synthesis and circularly polarized luminescence properties of BINOL-derived bisbenzofuro[2,3-b:3’,2’-e]pyridines (BBZFPys)
- Ryo Takishima,
- Yuji Nishii,
- Tomoaki Hinoue,
- Yoshitane Imai and
- Masahiro Miura
Beilstein J. Org. Chem. 2020, 16, 325–336, doi:10.3762/bjoc.16.32
- unsymmetrically substituted pyridines 3a–c in high yields. We then examined the oxidative cyclization of these compounds under the standard conditions adopting Pd(TFA)2 (30 mol %, TFA = trifluoroacetate) and AgOAc (3.0 equiv) as catalyst and oxidant, respectively, in pivalic acid as solvent (Scheme 3). Since the
Graphical Abstract
Scheme 1: Synthesis of BBFZPys through the Pd-catalyzed C–H/C–H coupling.
Scheme 2: Synthesis of 3a–c.
Scheme 3: Synthesis of 4a–c through oxidative coupling reaction.
Scheme 4: Synthesis of 6.
Figure 1: Absorption (dotted line) and fluorescence (solid line) spectra of 3, 4, and 6 measured as CHCl3 sol...
Figure 2: CD and CPL spectra of 3 measured as CHCl3 solutions (1.0 × 10−5 M) and in the solid states (dispers...
Figure 3: CD and CPL spectra of 4 and 6 measured as CHCl3 solutions (1.0 × 10−5 M) and in solid states (dispe...
Figure 4: ORTEP drawings of 4b and 4c with 50% thermal probability. Hydrogen atoms and solvent molecules are ...
Figure 5: Intramolecular stacking structures of 4b and 4c.
Copper-promoted/copper-catalyzed trifluoromethylselenolation reactions
- Clément Ghiazza and
- Anis Tlili
Beilstein J. Org. Chem. 2020, 16, 305–316, doi:10.3762/bjoc.16.30
- form C(sp)–SeCF3 bonds (Scheme 3) [18]. Therein, Dess–Martin periodinane (DMP) was used as the oxidant and potassium fluoride as the base, and the reactions were performed at room temperature in DMF as the solvent. The desired compounds were obtained in moderate to very good yields. Both electron
- and molecular oxygen as the oxidant, the substrates were successfully converted to the trifluoromethylselenylated analogs in good to very good yields. The substrate scope highlighted a broad functional group tolerance, including electron-withdrawing and -donating groups, heterocycles, and ferrocene
- already demonstrated its versatility in numerous processes. Nevertheless, its use in oxidative cross-coupling reactions requires stoichiometric amounts of the oxidant, which limits the attractiveness of the method in some cases. Finally, the newly developed electrophilic reagent TsSeCF3 also demonstrated
Graphical Abstract
Scheme 1: Process for the formation of C(sp3)–SeCF3 bonds with [(bpy)CuSeCF3]2 developed by the group of Weng....
Scheme 2: Trifluoromethylselenolation of vinyl and (hetero)aryl halides with [(bpy)CuSeCF3]2 by the group of ...
Scheme 3: Trifluoromethylselenolation of terminal alkynes using [(bpy)CuSeCF3]2 by the group of You and Weng.
Scheme 4: Trifluoromethylselenolation of carbonyl compounds with [(bpy)CuSeCF3]2 by the group of Weng.
Scheme 5: Trifluoromethylselenolation of α,β-unsaturated ketones with [(bpy)CuSeCF3]2 by the group of Weng.
Scheme 6: Trifluoromethylselenolation of acid chlorides with [(bpy)CuSeCF3]2 by the group of Weng.
Scheme 7: Synthesis of 2-trifluoromethylselenylated benzofused heterocycles with [(bpy)CuSeCF3]2 by the group...
Scheme 8: Difunctionalization of terminal alkenes and alkynes with [(bpy)CuSeCF3]2 by the group of Liang.
Scheme 9: Synthesis of Me4NSeCF3.
Scheme 10: Oxidative trifluoromethylselenolation of terminal alkynes and boronic acid derivatives with Me4NSeCF...
Scheme 11: Trifluoromethylselenolation of diazoacetates and diazonium salts with Me4NSeCF3 by the group of Goo...
Scheme 12: Trifluoromethylselenolation with ClSeCF3 by the group of Tlili and Billard.
Scheme 13: Trifluoromethylselenolation with TsSeCF3 by the group of Tlili and Billard.
Scheme 14: Copper-catalyzed synthesis of a selenylated analog 30 of Pretomanid developed by the group of Tlili...
Scheme 15: One-pot procedures for C–SeCF3 bond formations developed by Hor and Weng, Deng and Xiao, and Ruepin...
Recent developments in photoredox-catalyzed remote ortho and para C–H bond functionalizations
- Rafia Siddiqui and
- Rashid Ali
Beilstein J. Org. Chem. 2020, 16, 248–280, doi:10.3762/bjoc.16.26
- groundbreaking advancements were accomplished in this wonderful area of research, transforming a specific C–H bond effectively and selectively under favorable conditions (viz, room temperature, without external oxidant, cost-effective, sustainable, and environmentally friendly) still remains a highly challenging
- noteworthy renaissance not only because of the lower toxicity, stability, speed, and efficiency of the method, but also thanks to the easy generation of radical species and the formation of a long-lived triplet excited state under photoirradiation that can behave as a reductant as well as an oxidant [51][52
- metal catalysis, which include: (i) excellent regioselectivity of the targeted C–H bond formations thanks to favorable dissociation enthalpies and electronic properties as compared to other concurrent C–H bonds; (ii) avoidance of an extra oxidant because the reaction proceeds with overall redox
Graphical Abstract
Figure 1: List of photoredox catalysts used for C–H bond functionalizations.
Figure 2: List of metal-based photoredox catalysts used in this review article.
Figure 3: Jablonski diagram.
Figure 4: Photoredox catalysis via reductive or oxidative pathways. D = donor, A = acceptor, S = substrate, P...
Figure 5: Schematic representation of the combination of photoredox catalysis and transition metal catalysis.
Scheme 1: Weinreb amide C–H olefination.
Figure 6: Mechanism for the formation of 21 from 19 using photoredox catalyst 11.
Scheme 2: C–H olefination of phenolic ethers.
Scheme 3: Decarboxylative acylation of acetanilides.
Figure 7: Mechanism for the formation of 30 from acetanilide derivatives.
Scheme 4: Synthesis of fluorenone derivatives by intramolecular deoxygenative acylation of biaryl carboxylic ...
Figure 8: Mechanism for the photoredox-catalyzed synthesis of fluorenone derivatives.
Scheme 5: Synthesis of benzothiazoles via aerobic C–H thiolation.
Figure 9: Plausible mechanism for the construction of benzothiazoles from benzothioamides.
Scheme 6: Synthesis of benzothiazoles via oxidant-free C–H thiolation.
Figure 10: Mechanism involved in the synthesis of benzothiazoles via oxidant-free C–H thiolation.
Scheme 7: Synthesis of indoles via C–H cyclization of anilides with alkynes.
Scheme 8: Preparation of 3-trifluoromethylcoumarins via C–H cyclization of arylpropiolate esters.
Figure 11: Mechanistic pathway for the synthesis of coumarin derivatives via C–H cyclization.
Scheme 9: Monobenzoyloxylation without chelation assistance.
Figure 12: Plausible mechanism for the formation of 71 from 70.
Scheme 10: Aryl-substituted arenes prepared by inorganic photoredox catalysis using 12a.
Figure 13: Proposed mechanism for C–H arylations in the presence of 12a and a Pd catalyst.
Scheme 11: Arylation of purines via dual photoredox catalysis.
Scheme 12: Arylation of substituted arenes with an organic photoredox catalyst.
Scheme 13: C–H trifluoromethylation.
Figure 14: Proposed mechanism for the trifluoromethylation of 88.
Scheme 14: Synthesis of benzo-3,4-coumarin derivatives.
Figure 15: Plausible mechanism for the synthesis of substituted coumarins.
Scheme 15: Oxidant-free oxidative phosphonylation.
Figure 16: Mechanism proposed for the phosphonylation reaction of 100.
Scheme 16: Nitration of anilines.
Figure 17: Plausible mechanism for the nitration of aniline derivatives via photoredox catalysis.
Scheme 17: Synthesis of carbazoles via intramolecular amination.
Figure 18: Proposed mechanism for the formation of carbazoles from biaryl derivatives.
Scheme 18: Synthesis of substituted phenols using QuCN.
Figure 19: Mechanism for the synthesis of phenol derivatives with photoredox catalyst 8.
Scheme 19: Synthesis of substituted phenols with DDQ (5).
Figure 20: Possible mechanism for the generation of phenols with the aid of photoredox catalyst 5.
Scheme 20: Aerobic bromination of arenes using an acridinium-based photocatalyst.
Scheme 21: Aerobic bromination of arenes with anthraquinone.
Figure 21: Proposed mechanism for the synthesis of monobrominated compounds.
Scheme 22: Chlorination of benzene derivatives with Mes-Acr-MeClO4 (2).
Figure 22: Mechanism for the synthesis of 131 from 132.
Scheme 23: Chlorination of arenes with 4CzIPN (5a).
Figure 23: Plausible mechanism for the oxidative photocatalytic monochlorination using 5a.
Scheme 24: Monofluorination using QuCN-ClO4 (8).
Scheme 25: Fluorination with fluorine-18.
Scheme 26: Aerobic amination with acridinium catalyst 3a.
Figure 24: Plausible mechanism for the aerobic amination using acridinium catalyst 3a.
Scheme 27: Aerobic aminations with semiconductor photoredox catalyst 18.
Scheme 28: Perfluoroalkylation of arenes.
Scheme 29: Synthesis of benzonitriles in the presence of 3a.
Figure 25: Plausible mechanism for the synthesis of substituted benzonitrile derivatives in the presence of 3a....
Synthesis of 4-(2-fluorophenyl)-7-methoxycoumarin: experimental and computational evidence for intramolecular and intermolecular C–F···H–C bonds
- Vuyisa Mzozoyana,
- Fanie R. van Heerden and
- Craig Grimmer
Beilstein J. Org. Chem. 2020, 16, 190–199, doi:10.3762/bjoc.16.22
- ], anti-oxidant [7], antibacterial [8], hepatoprotective, anticoagulant, antiviral and antithrombotic activities [9]. The variety of uses of these compounds resulted in an increase in demand for large quantities of coumarins. Due to an insufficient natural supply to meet this demand for these compounds
Graphical Abstract
Scheme 1: Synthesis of 4-(2-fluorophenyl)-7-methoxycoumarin (6).
Figure 1: 1H NMR spectra for the “aromatic” region of coumarin 6; comparison of 1H spectrum and 1H-{19F} spec...
Figure 2: 13C NMR spectra for coumarin 5 and 6; showing the splitting of the signal corresponding to C5.
Figure 3: 19F,1H-HOESY NMR spectrum for coumarin 6 illustrating two through-space interactions.
Figure 4: Superposition of single-crystal X-ray structure (red) and DFT-optimized structure (green); RMSD 0.3...
Figure 5: DFT-optimized structure for coumarin (6).
Figure 6: Plots of relative energy (black trace, no units), interatomic distance F–H5 (red trace, Å), interat...
Figure 7: Short contacts within the single-crystal X-ray structure of coumarin 6.
Synthesis of 3-alkenylindoles through regioselective C–H alkenylation of indoles by a ruthenium nanocatalyst
- Abhijit Paul,
- Debnath Chatterjee,
- Srirupa Banerjee and
- Somnath Yadav
Beilstein J. Org. Chem. 2020, 16, 140–148, doi:10.3762/bjoc.16.16
- -withdrawing groups, using Pd(OAc)2 as catalyst and Cu(OAc)2 as oxidant [25]. Since then, several variants of the reaction involving Pd catalysis and various oxidants have been reported for the synthesis of 3-alkenylindoles. For example, Chen et al. and Huang et al. independently reported the C3 alkenylation
- of indoles using Pd(OAc)2 and Pd(II)/polyoxometallate, respectively, as a catalyst and molecular oxygen as the oxidant [26][27]. Verma and co-workers used the reaction between indoles and alkenes in the presence of a Pd(OAc)2 catalyst, a Cu(OAc)2 oxidant, and a 2-(1-benzotriazolyl)pyridine ligand [28
- ]. Noël and co-workers reported the C3–H olefination of indoles using Pd(OAc)2 as a catalyst and molecular oxygen as the oxidant under continuous flow conditions [29]. Jia et al. reported the synthesis of 3-alkenylindoles using Pd(OAc)2 as the catalyst and MnO2 as the oxidant under ball milling conditions
Graphical Abstract
Figure 1: Biologically and medicinally important 3-alkenylindoles.
Scheme 1: a) Previous and b) present work related to the synthesis of 3-alkenylindoles.
Scheme 2: Substrate scope for the C–H alkenylation of the indoles 1. Reaction conditions: 1 (1 mmol), 2 (2 mm...
Scheme 3: a) Three-phase test to determine a homogeneous or heterogeneous catalytic mechanism of action for t...
Scheme 4: Probable catalytic mechanism for the transformation of 1a by the RuNC.
