Recent developments in enantioselective photocatalysis

• Callum Prentice,
• James Morrisson,
• Andrew D. Smith and
• Eli Zysman-Colman

Beilstein J. Org. Chem. 2020, 16, 2363–2441, doi:10.3762/bjoc.16.197

• electron transfer (SET) steps photoinitiated using visible light as the energy source, often leading to the generation of radicals and subsequent reaction of these radicals with the ground-state substrates [3]. Energy transfer catalysis is another significant branch of photocatalysis, in which

• transformative synthetic strategy, including in enantioselective synthesis. From the pioneering work by MacMillan [1] and Bach [2], enantioselective photocatalysis has grown into a well-established field of its own. A large proportion of photocatalysis focuses on photoredox catalysis, which involves single

Photosensitized direct C–H fluorination and trifluoromethylation in organic synthesis

• Shahboz Yakubov and
• Joshua P. Barham

Beilstein J. Org. Chem. 2020, 16, 2151–2192, doi:10.3762/bjoc.16.183

• reactions proceed under photoredox catalysis (PRC), involving Dexter electron transfer. Such photoredox reactions begin with the excitation of the photocatalyst (PC) by visible light, followed by a single-electron transfer (SET) between the excited photocatalyst and another molecule (quencher, Scheme 2A

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

• ], and chromium trioxide (CrO3), which, based on its Cr(VI) oxidation state, should be able to facilitate single-electron transfer in the presence of electron-rich arenes. The dimerization of 1,2,4-trimethoxynaphthalene (17) in the presence of the metal oxidants CAN, V2O5, and CrO3, afforded binaphthyl

A complementary approach to conjugated N-acyliminium formation through photoredox-catalyzed intermolecular radical addition to allenamides and allencarbamates

• Olusesan K. Koleoso,
• Matthew Turner,
• Felix Plasser and
• Marc C. Kimber

Beilstein J. Org. Chem. 2020, 16, 1983–1990, doi:10.3762/bjoc.16.165

• each reaction shown in Scheme 4. A tentative mechanism for this transformation is described in Scheme 5a. Excitation of the Ir(III) complex 17 provides *Ir(III) that subsequently undergoes reductive quenching by Et3N, delivering Ir(II) [48]. Single electron transfer from Ir(II) to 18 then generates an

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

• as sole oxidant and implementing two photoredox cycles is presented in Figure 16. After a ligand exchange, Co(II) undergoes a single-electron transfer (SET) oxidation to Co(III) with a concomitant formation of the reduced organic photocatalyst. The thus generated highly reactive Co(III) complex

• photoredox catalysis. This interception leads to a new metallic key intermediate 3 by single-electron transfer (SET). The desired coupling product 4 is then obtained after a reductive elimination (Figure 19). Applying such an approach paved the way towards unprecedented couplings benefiting from a SET

• single electron-transfer process (Figure 36). In the first place, a bidentate chelated species is formed by the coordination of 1-naphthylamine derivatives with copper salt. The subsequent oxidation of this intermediate with potassium persulfate produces a Cu(III) species, furnishing a radical cation on

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

• visible light through single-electron transfer processes, now referred to as visible light photoredox catalysis (PRC). A similar query on the Web of Science for the term “Photoredox” clearly shows the surge in PRC research following those reports, from 2010 onwards (Figure 1A). However, what is

An overview on disulfide-catalyzed and -cocatalyzed photoreactions

• Yeersen Patehebieke

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

• alcohol by the thiyl radical produces thiophenol and an allylic radical. Next, the single-electron transfer (SET) from the allylic radical to another thiyl radical generates the allylic cation. Subsequently, the proton abstraction from the hydroxy group by the SET-generated thiolate gives the final

Distinctive reactivity of N-benzylidene-[1,1'-biphenyl]-2-amines under photoredox conditions

• Shrikant D. Tambe,
• Kwan Hong Min,
• Naeem Iqbal and
• Eun Jin Cho

Beilstein J. Org. Chem. 2020, 16, 1335–1342, doi:10.3762/bjoc.16.114

• -coupled single-electron transfer in the presence of an Ir photocatalyst. On the other hand, symmetrical 1,2-diamines were selectively produced from the same starting materials by the judicious choice of the reaction conditions, showcasing the distinct reactivity of N-benzylidene-[1,1'-biphenyl]-2-amines

• quenched by single-electron transfer from Cy2NMe, resulting in the generation of the highly reducing [IrII] species and the radical cation A. To validate the reductive quenching pathway, we carried out Stern−Volmer quenching experiments (Figure S1, Supporting Information File 1). The emission intensity of

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

• photocatalysts interact with organic molecules via three main pathways: electron transfer (ET), EnT, and atom transfer (AT). In the first case (Scheme 1, box 1), the excited photocatalyst (PC*) undergoes a single-electron transfer (SET) with a suitable electron acceptor A or electron donor D. In an oxidative

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

• , 68502-100, Brazil 10.3762/bjoc.16.83 Abstract In this review we present relevant and recent applications of porphyrin derivatives as photocatalysts in organic synthesis, involving both single electron transfer (SET) and energy transfer (ET) mechanistic approaches. We demonstrate that these highly

• adequate tuning of the porphyrin properties can enable them to absorb light in almost all of the UV–vis spectral range. Porphyrins also have elevated molar absorptivity (ca 105 L·mol−1·cm−1) and appropriate electronic levels for both energy transfer (ET) and single electron transfer (SET) in many

• porphyrin is in the triplet excited state, two distinct processes can be observed: a) single electron transfer (SET); and b) energy transfer (Figure 2) [12][13][14]. The first involves the exchange of electrons between the porphyrin and the substrate by an oxidative or reductive process, and the second

Copper catalysis with redox-active ligands

• Agnideep Das,
• Yufeng Ren,
• Cheriehan Hessin and
• Marine Desage-El Murr

Beilstein J. Org. Chem. 2020, 16, 858–870, doi:10.3762/bjoc.16.77

• phenols, ketones and 1,3-dienes (Scheme 6) [27]. C–C bond formation Complexes of radical and redox-active ligands with transition metals are known to be able to promote radical reactions through single-electron transfer (SET) processes [28]. Expanding on the research area pioneered by Wieghardt and

Aldehydes as powerful initiators for photochemical transformations

• Maria A. Theodoropoulou,
• Nikolaos F. Nikitas and
• Christoforos G. Kokotos

Beilstein J. Org. Chem. 2020, 16, 833–857, doi:10.3762/bjoc.16.76

• aliphatic acids and the coupling of the residual chain with various electrophiles. Metal-based catalysts are common in reactions that require a high redox potential for a single electron transfer (SET) procedure to take place. On the other hand, even if organocatalysts have lower redox potentials, they are

• yield. The drop in the yield was insignificant in the absence of oxygen. An insignificant drop in the yield was also noticed when an electron scavenger, CuCl2, was added to the reaction mixture, excluding a single electron transfer process. When a triplet state quencher, anthracene, was added, the

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

• radical pathway as the one described previously (Scheme 3). This mechanism involved the formation of a CF3 radical through a single-electron transfer between the excited complex [Cu(I)(dap)2]+* and triflyl chloride. This radical added to the alkene, and the SO2Cl anion coordinated to the [Cu(II)] species

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

• functionalization has been done either using transition metal catalysis or organocatalysis, through the installation of directing groups next to the targeted C–H bond, or by employing radical tactics based on single-electron transfer (SET) [15][16][17][18][19][20][21][22][23][24][25][26][27]. Although

Recent advances in transition-metal-catalyzed incorporation of fluorine-containing groups

• Xiaowei Li,
• Xiaolin Shi,
• Xiangqian Li and
• Dayong Shi

Beilstein J. Org. Chem. 2019, 15, 2213–2270, doi:10.3762/bjoc.15.218

• for product formation and a successful outcome of the reaction. In the same year, the Ritter group [52] reported a Pd-catalyzed fluorination of arylboronic acid derivatives via a Pd(II)/Pd(III) cycle (Scheme 15). A single-electron-transfer (SET) mechanism involving a well-defined Pd(III) intermediate

A review of the total syntheses of triptolide

• Xiang Zhang,
• Zaozao Xiao and
• Hongtao Xu

Beilstein J. Org. Chem. 2019, 15, 1984–1995, doi:10.3762/bjoc.15.194

• for the generation of carbon radicals via single-electron transfer (SET). In 2016, Barriault and co-workers reported a methodology that features the utilization of dimeric gold complex [Au2(dppm)2]Cl2 and ultraviolet A (UV, 365 nm) light to direct arylation of bromide-substituted butenolides or cyclic

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

• single-electron transfer (SET) with CuI followed by hydride abstraction/intramolecular nucleophilic addition and loss of a proton forming the desired compound 49 (Scheme 19). Cu(I)-catalyzed intramolecular oxidative C–H amidation of N-pyridylenaminones 61 for the synthesis of imidazo[1,2-a]pyridine

• not formed. Atmospheric oxygen has oxidized Cu(I) to Cu(II). This Cu(II) acts as an initiator for a single electron transfer (SET) process, to proceed the reaction with benzylamine. A regioselective synthesis of imidazo[1,2-a]pyridines was reported by the group of Kamal and Reddy [123]. They have

A diastereoselective approach to axially chiral biaryls via electrochemically enabled cyclization cascade

• Hong Yan,
• Zhong-Yi Mao,
• Zhong-Wei Hou,
• Jinshuai Song and
• Hai-Chao Xu

Beilstein J. Org. Chem. 2019, 15, 795–800, doi:10.3762/bjoc.15.76

• at the cathode deprotonates 2a to give its conjugate base II. The anionic II is oxidized by radical cation I through single electron transfer (SET) to give radical intermediate III, which undergoes a biscyclization to give V. Further oxidation of V followed by hydrolysis of the cyclic carbamate

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

• usually proceeds through single-electron transfer to dioxygen, leading to either a loss of stereoselectivity, degradation of the organocopper or to the formation of dimer as major products [71]. Therefore, it was clear that a different approach for the oxidation process was needed. Oxenoid, possessing the

Oxidative radical ring-opening/cyclization of cyclopropane derivatives

• Yu Liu,
• Qiao-Lin Wang,
• Zan Chen,
• Cong-Shan Zhou,
• Bi-Quan Xiong,
• Pan-Liang Zhang,
• Chang-An Yang and
• Quan Zhou

Beilstein J. Org. Chem. 2019, 15, 256–278, doi:10.3762/bjoc.15.23

• reaction pathway is outlined in Scheme 13. Initially, the Togni reagent II (30) goes through a single-electron transfer (SET) under the action of Fe2+ to generate the CF3 radical 35. The CF3 radical 35 is trapped by the C–C double bond of substrate 54 to produce the alkyl radical intermediate 57. Then, the

• of azide to Rh2(esp)2 complex (bis[rhodium-(α,α,α’,α’-tetramethyl-1,3-benzenedipropionic acid)]) and extrusion of N2. Then, the Rh-nitrene intermediate 65 goes through an intramolecular single electron transfer (SET) to give the nitrogen-centered radical intermediate 66 [87][88][89][90]. Next, the

N-Arylphenothiazines as strong donors for photoredox catalysis – pushing the frontiers of nucleophilic addition of alcohols to alkenes

• Fabienne Speck,
• David Rombach and
• Hans-Achim Wagenknecht

Beilstein J. Org. Chem. 2019, 15, 52–59, doi:10.3762/bjoc.15.5

• conditions or heated ion exchange resin [21][22]. These methods are therefore not suitable for the alkoxylation of acid or base-labile substrates. To overcome the current limitations of reduction potentials of single electron transfer processes in photoredox catalysis we present herein a range of new N

Organometallic vs organic photoredox catalysts for photocuring reactions in the visible region

• Aude-Héloise Bonardi,
• Frédéric Dumur,
• Guillaume Noirbent,
• Jacques Lalevée and
• Didier Gigmes

Beilstein J. Org. Chem. 2018, 14, 3025–3046, doi:10.3762/bjoc.14.282

• triplet excited state through metal to ligand charge transfer (Scheme 3, reaction 1). As described in Table 2, the irradiation must be around 450 nm. Thus, as the triplet excited state is long enough and thanks to the values of oxidation potentials, a single electron transfer (SET) to the iodonium salt

• processes: intramolecular photochemical processes and/or photoredox processes. In this review, we will focus only on photoredox processes. In a photoredox-controlled radical polymerization, a photoredox catalyst is used. By irradiation, it undergoes a single electron transfer with an appropriate initiator

• to go to its excited state and then oxidized by the initiator or the dormant species (R-Mn-Br) [102]. To regenerate the PC, a single electron transfer reaction must be involved as shown in Scheme 8. Through these single electron transfer processes, photo-ATRP has been successfully achieved (ATRP

Photocatalyic Appel reaction enabled by copper-based complexes in continuous flow

• Clémentine Minozzi,
• Jean-Christophe Grenier-Petel,
• Shawn Parisien-Collette and
• Shawn K. Collins

Beilstein J. Org. Chem. 2018, 14, 2730–2736, doi:10.3762/bjoc.14.251

• ]. Specifically, our group has demonstrated that heteroleptic Cu(I) complexes [19][20][21] have significant potential as photocatalysts that can promote a variety of mechanistically distinct photochemical transformations including single electron transfer (SET), energy transfer (ET), and proton-coupled electron

Cobalt-catalyzed peri-selective alkoxylation of 1-naphthylamine derivatives

• Jiao-Na Han,
• Cong Du,
• Xinju Zhu,
• Zheng-Long Wang,
• Yue Zhu,
• Zhao-Yang Chu,
• Jun-Long Niu and
• Mao-Ping Song

Beilstein J. Org. Chem. 2018, 14, 2090–2097, doi:10.3762/bjoc.14.183

• calculations (DFT) [30][31], the C–H activation most possibly proceeded via a single-electron transfer (SET) path compared to a concerted metalation-deprotonation (CMD) path. Followed by an intermolecular SET process, the cation-radical intermediate A was generated, which coordinates with a CoIII species to

Functionalization of graphene: does the organic chemistry matter?

• Artur Kasprzak,
• Agnieszka Zuchowska and
• Magdalena Poplawska

Beilstein J. Org. Chem. 2018, 14, 2018–2026, doi:10.3762/bjoc.14.177

• species (Figure 7, step a). Then (most likely) the aryl radical is obtained from the diazonium salt via the single electron transfer (SET) process and the inclusion of a graphene sheet (Figure 7, step b). This reaction step results in nitrogen extrusion. The desired functionalization route is most

• ) reaction of the activated carboxyl group with water molecules. Mechanism of the covalent functionalization of graphene-family material applying diazonium salts chemistry: (a) generation of the diazonium salt, (b) single electron transfer (SET) between diazonium salt and graphene-family material, (c