Visible-light-mediated copper photocatalysis for organic syntheses

• Yajing Zhang,
• Qian Wang,
• Zongsheng Yan,
• Donglai Ma and
• Yuguang Zheng

Beilstein J. Org. Chem. 2021, 17, 2520–2542, doi:10.3762/bjoc.17.169

• cation I and a CuI species. This process regenerated CuII in the presence of molecular oxygen. The deprotonation of the nitrogen radical cation produces an α–amino radical II, which was further oxidized to the iminium ion III to which the copper alkynylide added forming the desired product (Scheme 17

• to generate the CuII hydroperoxo complex C and the corresponding aldehyde. Complex C can undergo a reductive elimination to recover 64a. The liberated aminobenzamide 64a and the aldehyde undergo a condensation reaction to produce quinazolinone 66′, followed by oxidation with molecular oxygen to

On the application of 3d metals for C–H activation toward bioactive compounds: The key step for the synthesis of silver bullets

• Renato L. Carvalho,
• Amanda S. de Miranda,
• Mateus P. Nunes,
• Roberto S. Gomes,
• Guilherme A. M. Jardim and
• Eufrânio N. da Silva Júnior

Beilstein J. Org. Chem. 2021, 17, 1849–1938, doi:10.3762/bjoc.17.126

Cerium-photocatalyzed aerobic oxidation of benzylic alcohols to aldehydes and ketones

• Girish Suresh Yedase,
• Sumit Kumar,
• Jessica Stahl,
• Burkhard König and
• Veera Reddy Yatham

Beilstein J. Org. Chem. 2021, 17, 1727–1732, doi:10.3762/bjoc.17.121

• [7][8][9][10][11][12][13][14][15][16][17]. In order to overcome the limitations, various homogeneous and heterogeneous catalytic oxidation systems have been reported. Aerobic oxidation is particularly attractive as it allows the transformations under mild reaction conditions with molecular oxygen

A comprehensive review of flow chemistry techniques tailored to the flavours and fragrances industries

• Guido Gambacorta,
• James S. Sharley and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2021, 17, 1181–1312, doi:10.3762/bjoc.17.90

A new and efficient methodology for olefin epoxidation catalyzed by supported cobalt nanoparticles

• Lucía Rossi-Fernández,
• Viviana Dorn and
• Gabriel Radivoy

Beilstein J. Org. Chem. 2021, 17, 519–526, doi:10.3762/bjoc.17.46

• greener oxidizing agents as molecular oxygen, hydrogen peroxide or tert-butyl hydroperoxide (TBHP) [14][15][16][17]. However, using any of these oxidants alone results in considerable low reactivity and selectivity in olefin epoxidation reactions. Thus, several transition-metal-based catalytic methods

• the other hand, the use of supported cobalt nanoparticles as efficient catalysts for the epoxidation of olefins has received increasing attention in the last years. In most cases, a crucial influence of the support (TiO2, HAP, CNTs, SBA, SiO2), the oxidant agent (molecular oxygen or TBHP) and the

• solvent (DMF, MeCN, ethyl acetate, DMSO, solvent free) on the activity and selectivity of the nanocatalysts has been noted [27][41][42][43][44]. Furthermore, all the reported methodologies use either molecular oxygen together with an aldehyde as a co-reductant, or only a “green” peroxide (H2O2, TBHP) as

Biochemistry of fluoroprolines: the prospect of making fluorine a bioelement

• Vladimir Kubyshkin,
• Rebecca Davis and
• Nediljko Budisa

Beilstein J. Org. Chem. 2021, 17, 439–460, doi:10.3762/bjoc.17.40

• modifications of proline residues are sparse. The most common among them is hydroxylation at position 4 by molecular oxygen, which is mediated by prolyl-4-hydroxylase [34]. This process has a remarkable relevance in the stabilization of collagen in higher organisms [35]. The experimental expression of the

Synthetic approaches to bowl-shaped π-conjugated sumanene and its congeners

• Shakeel Alvi and
• Rashid Ali

Beilstein J. Org. Chem. 2020, 16, 2212–2259, doi:10.3762/bjoc.16.186

• corresponding trimethylsumanene 28 by means of nucleophilic oxidation using NaHMDS in the presence of molecular oxygen in DMF as the solvent (Scheme 8). It has been noticed from the literature that the directly linked π-conjugated systems act as promising electron-accepting materials because of their high LUMO

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

• 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

• photoredox catalysis (Figure 5) [73]. The coupling products were generally isolated in good yields, although this procedure required high temperature (120 °C). Remarkably, molecular oxygen was used as the terminal oxidizing agent of the overall C–H functionalization reaction. The mechanistic studies revealed

• of the photocatalyst in the absence of oxygen, suggesting that a direct electron transfer from the photosensitizer allowed the reoxidation of the active catalyst. However, the participation of molecular oxygen cannot be excluded. Rueping further demonstrated the capacity of the dual catalytic systems

Heterogeneous photocatalysis in flow chemical reactors

• Christopher G. Thomson,
• Ai-Lan Lee and
• Filipe Vilela

Beilstein J. Org. Chem. 2020, 16, 1495–1549, doi:10.3762/bjoc.16.125

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

• 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

• phosphate base (50 mol %). Thus, the latter played a key role in the PCET event which triggered the activation of the N–H bond in 18.1a–d and led to the N-centered radicals 18.2·a–d. Ensuing cyclization onto the pendant aromatic group, followed by rearomatization enabled by molecular oxygen, gave the

An overview on disulfide-catalyzed and -cocatalyzed photoreactions

• Yeersen Patehebieke

Beilstein J. Org. Chem. 2020, 16, 1418–1435, doi:10.3762/bjoc.16.118

• attractive because the reagents involved in the reaction process are simple and inexpensive, plus they only require molecular oxygen or air. In addition, disulfide-catalyzed cyclization reactions are also very effective for the generation of five- and six-membered rings. The unique high selectivity and

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

• -position to the oxime group (70i,j) were obtained with good yields. The formation of 70i and 70j is impossible through an intermediate similar to intermediate 68 in Scheme 24. Oxidative cyclization of N-benzyl amidoximes 71 was realized [117] under the action of molecular oxygen with the formation of

• 1,2,4-oxadiazolines 88 by oxidative cyclization of amidoximes 87 under the action of molecular oxygen and visible light in the presence of catalytic amounts of 2,4,6-tris(4-fluorophenyl)pyrilium tetrafluoroborate (T(p-F)PPT) was proposed (Scheme 32) [122]. Pyrrolidinyl oxime derivatives having both

• endocyclic, high stereoselectivity was observed with the formation of trans-products (examples 106c and 108b). The oxidative cyclization of β,γ-unsaturated oximes 109 under the action of molecular oxygen and catalytic amounts of bis(5,5-dimethyl-1-(4-methylpiperazin-1-yl)hexane-1,2,4-trione)cobalt(II) (Co

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

• state PC. In most cases, Sub* is in the triplet state if it is an organic molecule. A common exception to this is molecular oxygen, which upon excitation attains a more reactive singlet state. In the third mode of activation, atom transfer (AT, Scheme 1, box 3), the excited state photocatalyst PC* can

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

• involves energy transfer to surrounding molecules, such as molecular oxygen, heterocycles and other relevant molecules [15][16][17]. The excited states of porphyrins are also both potent oxidants and reductants when compared to the ground state. This phenomenon can be measured by the comparison of the

• molecular oxygen (triplet state). In this process, well-known singlet oxygen (1O2) is generated. Singlet oxygen can be considered a very versatile reagent in organic synthesis since it promotes many mild oxidation processes instead of combustion [23][57][58][59][60]. This excited state form of molecular

• brominated tin porphyrin (SnTBPP) as monomer (Scheme 47). The irradiation of this material in the presence of both sulfides and molecular oxygen furnished a variety of sulfoxides in 70–97% yields. The SnPor@PAF presented the same photocatalytic activity of its monomer (SnTBPP) with the advantage of its easy

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

• 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

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

• of molecular oxygen as an oxidant. Although various photoredox catalysts and solvents were examined, the best results were obtained with photoredox catalyst 6 in chlorinated solvents. In the absence of a photoredox catalyst, the goup did not observe any product formation. A list of products assembled

• observed a number of interesting facts, viz: (i) the reaction proceeded with environmentally friendly molecular oxygen as oxidant, (ii) water was the only byproduct of the reaction, (iii) no reaction occurred without the involvement of a photocatalyst, (iv) high yields were obtained with electron-donating

• photolysis. The mechanism involved in this transformation is shown in Figure 20. Aryl C–H halogenation Aerobic bromination of arenes: In another experiment, Ohkubo et al. reported that for aerobic aryl C–H brominations, HBr can be utilized with photoredox catalyst 2 in the presence of molecular oxygen to

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

• 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

• [30]. Das and co-workers reported the C3–H alkenylation of 7-azaindole using Pd(OAc)2 as a catalyst, Ph3P as a ligand, and Cu(OTf)2 as an oxidative cocatalyst, with molecular oxygen as the oxidant [31]. Carrow and co-workers reported mechanistic, kinetic, and selectivity studies of the C–H

Excited state dynamics for visible-light sensitization of a photochromic benzil-subsituted phenoxyl-imidazolyl radical complex

• Yoichi Kobayashi,
• Yukie Mamiya,
• Katsuya Mutoh,
• Hikaru Sotome,
• Masafumi Koga,
• Hiroshi Miyasaka and
• Jiro Abe

Beilstein J. Org. Chem. 2019, 15, 2369–2379, doi:10.3762/bjoc.15.229

• similar to that of PIC and because the fast decay component does not depend on the molecular oxygen, the fast and slow decay components can be assigned to the biradical form generated by the C–N bond breaking and the T1 state of Benzil-PIC, respectively. It is worth mentioning that the T1 state of Benzil

Recent advances on the transition-metal-catalyzed synthesis of imidazopyridines: an updated coverage

• Gagandeep Kour Reen,
• Ashok Kumar and
• Pratibha Sharma

Beilstein J. Org. Chem. 2019, 15, 1612–1704, doi:10.3762/bjoc.15.165

• halide substituent in the product which was successfully overcome by this protocol along with the synthesis of pyrazines and pyrimidines in high yield (Scheme 3). Furthermore, easy functionalization of the products from the viewpoint of reactive halide made them valuable synthons. Molecular oxygen used

Diastereo- and enantioselective preparation of cyclopropanol derivatives

• Marwan Simaan and
• Ilan Marek

Beilstein J. Org. Chem. 2019, 15, 752–760, doi:10.3762/bjoc.15.71

• attention to their stereoselective oxidation reaction (Scheme 5). Considering electrophilic oxidation processes of organometallic species, molecular oxygen seems to be the most obvious choice due to its abundancy and low cost. Nevertheless, the reaction of molecular oxygen with a organocopper species

Selective benzylic C–H monooxygenation mediated by iodine oxides

• Kelsey B. LaMartina,
• Haley K. Kuck,
• Linda S. Oglesbee,
• Asma Al-Odaini and
• Nicholas C. Boaz

Beilstein J. Org. Chem. 2019, 15, 602–609, doi:10.3762/bjoc.15.55

• ) scaffold have been intensely studied for their ability to mediate hydrogen atom abstraction using a terminal oxidant of molecular oxygen [40][41][42][43][44][45]. NHPI has also been used in the effective C–H to C–O functionalization of benzylic positions using oxidants other than molecular oxygen including

Tandem copper and photoredox catalysis in photocatalytic alkene difunctionalization reactions

• Nicholas L. Reed,
• Madeline I. Herman,
• Vladimir P. Miltchev and
• Tehshik P. Yoon

Beilstein J. Org. Chem. 2019, 15, 351–356, doi:10.3762/bjoc.15.30

• dioxygen for this purpose is frequently exploited to effect synthetically useful copper-catalyzed aerobic oxidation reactions [27][28]. However, the use of molecular oxygen as a terminal oxidant presents unique challenges in photoredox chemistry. Triplet dioxygen rapidly quenches the excited state of most

Degenerative xanthate transfer to olefins under visible-light photocatalysis

• Atsushi Kaga,
• Xiangyang Wu,
• Joel Yi Jie Lim,
• Hirohito Hayashi,
• Yunpeng Lu,
• Edwin K. L. Yeow and
• Shunsuke Chiba

Beilstein J. Org. Chem. 2018, 14, 3047–3058, doi:10.3762/bjoc.14.283

• purification of the desired products. A combination of triethylborane (Et3B) and molecular oxygen can also initiate the reaction at lower temperature (e.g., room temperature), while the employment of Et3B is hampered due to its pyrophoric nature under aerobic conditions as well as undesired Et3B-mediated

Synthesis of indole–cycloalkyl[b]pyridine hybrids via a four-component six-step tandem process

• Muthumani Muthu,
• Rakkappan Vishnu Priya,
• Abdulrahman I. Almansour,
• Raju Suresh Kumar and
• Raju Ranjith Kumar

Beilstein J. Org. Chem. 2018, 14, 2907–2915, doi:10.3762/bjoc.14.269

• cyclization with the carbonyl to give 11, which subsequently undergoes dehydration to yield the cyclododeca[b]pyridine-3-carbonitrile 12. The intermediate 12 upon oxidative aromatization by molecular oxygen as the sole oxidant yields the indole–cyclododeca[b]pyridine-3-carbonitrile 7f. This four-component

An overview on recent advances in the synthesis of sulfonated organic materials, sulfonated silica materials, and sulfonated carbon materials and their catalytic applications in chemical processes

• Hashem Sharghi,
• Pezhman Shiri and
• Mahdi Aberi

Beilstein J. Org. Chem. 2018, 14, 2745–2770, doi:10.3762/bjoc.14.253

• carbonyl of acetylacetone 90 to form enamine intermediate II. In the next step, hydroxyl radicals are produced through activation of molecular oxygen in the presence of SSA. Intermediate III is created via the addition of a hydroxyl radical to enamine II. This intermediate loses hydrogen radical to form