Application of N-heterocyclic carbene–Cu(I) complexes as catalysts in organic synthesis: a review

• Nosheen Beig,
• Varsha Goyal and
• Raj K. Bansal

Beilstein J. Org. Chem. 2023, 19, 1408–1442, doi:10.3762/bjoc.19.102

• primary, secondary, and tertiary alkyl halides. The mechanistic investigation revealed the generation of a silyl–copper intermediate which activates the alkyl halides by a single electron transfer to form alkyl radical intermediates [54]. It was suggested that substituting B2pin2 for PhMe2Si-Bpin would

Visible-light-induced nickel-catalyzed α-hydroxytrifluoroethylation of alkyl carboxylic acids: Access to trifluoromethyl alkyl acyloins

• Feng Chen,
• Xiu-Hua Xu,
• Zeng-Hao Chen,
• Yue Chen and
• Feng-Ling Qing

Beilstein J. Org. Chem. 2023, 19, 1372–1378, doi:10.3762/bjoc.19.98

• pivalic anhydride as activator to afford Ni(II) intermediate F. Subsequently, trapping of the alkyl radical C generates high-valent Ni(III) intermediate G, which undergoes facile reductive elimination to furnish the final coupling product 3 and Ni(I) intermediate H. The single-electron transfer (SET

Non-noble metal-catalyzed cross-dehydrogenation coupling (CDC) involving ether α-C(sp³)–H to construct C–C bonds

• Hui Yu and
• Feng Xu

Beilstein J. Org. Chem. 2023, 19, 1259–1288, doi:10.3762/bjoc.19.94

• bonds The possible mechanism of the CDC reaction involving ether α-C(sp3)–H bonds mainly follows the two pathways outlined in Scheme 2. Route a: First, the C(sp3)–H bond at the α-position of the oxygen atom undergoes a single-electron transfer under the combined action of the transition metal and an

• extract a hydrogen from the ether C (sp3)–H bond to form radicals. Subsequently, a single electron transfer (SET) leads to the oxonium species. Then, the enamine generated in situ from methyl aryl ketone and pyrrolidine undergoes a nucleophilic reaction with the oxonium species followed by hydrolysis to

• of the radical initiator to the ether to obtain the corresponding ether radical species. The coupling product is accessed through a single electron transfer (SET) and other transformations. In 2019, Tu et al. established a highly efficient Cu-catalyzed cross-dehydrogenative coupling to access a

Radical ligand transfer: a general strategy for radical functionalization

• David T. Nemoto Jr,
• Kang-Jie Bian,
• Shih-Chieh Kao and
• Julian G. West

Beilstein J. Org. Chem. 2023, 19, 1225–1233, doi:10.3762/bjoc.19.90

• Fe(II/III) cycle is proposed, where a single electron transfer from Fe(II) reduces the peroxyester and produces a carboxyl radical and Fe(III), which can coordinate an azide ligand. Rapid decarboxylation produces the transient alkyl radical which can be asymmetrically azidated by RLT from an Fe(III

Enabling artificial photosynthesis systems with molecular recycling: A review of photo- and electrochemical methods for regenerating organic sacrificial electron donors

• Grace A. Lowe

Beilstein J. Org. Chem. 2023, 19, 1198–1215, doi:10.3762/bjoc.19.88

Exploring the role of halogen bonding in iodonium ylides: insights into unexpected reactivity and reaction control

• Carlee A. Montgomery and
• Graham K. Murphy

Beilstein J. Org. Chem. 2023, 19, 1171–1190, doi:10.3762/bjoc.19.86

• cycloaddition reactions that occur without transition metal catalysts, the unexpected initiation of single electron transfer (SET) processes or photochemical transformations, and even proton transfers that appear to defy pKa limitations. The reaction pathways followed by iodonium ylides and Lewis basic reaction

• , they believed that the reaction was likely initiated by either single electron transfer between the reagents (not shown), or by electrophilic addition of the olefin onto the ylide, forming intermediate adduct 17. This was followed by formation of iodocycle 18, from which reductive elimination of

• as an electron donor–acceptor complex) [121], and this bonding description has recently been used to support proposals for single electron transfer (SET) reaction pathways between iodonium ylides and various halogen bond acceptors. Alternatively, halogen-bonded complexes of iodonium ylides could lead

Selective and scalable oxygenation of heteroatoms using the elements of nature: air, water, and light

• Damiano Diprima,
• Hannes Gemoets,
• Stefano Bonciolini and
• Koen Van Aken

Beilstein J. Org. Chem. 2023, 19, 1146–1154, doi:10.3762/bjoc.19.82

• separate” additives, a significant rate enhancement could be obtained with a positive impact on productivity rates. Results and Discussion There are a lot of similarities between electrochemistry and photoredox chemistry [33] as both rely on single-electron transfer processes to initiate reactions. In

• irradiation at 310 nm [27]. They concluded that both a single-electron transfer and a singlet oxygen path can occur depending on the nature of the compound. Intriguingly, the current method applies 365 nm irradiation at which thioanisole does not absorb (Supporting Information File 1, Figure S1). Also, the

• originates from water. In this tentative mechanism, the sulfide I forms with water and oxygen a photoactive complex II which is excited at 365 nm towards III. Via single-electron transfer both a radical cation IV and the superoxide V are generated. Subsequently, the sulfide radical cation IV undergoes a

Photoredox catalysis harvesting multiple photon or electrochemical energies

• Mattia Lepori,
• Simon Schmid and
• Joshua P. Barham

Beilstein J. Org. Chem. 2023, 19, 1055–1145, doi:10.3762/bjoc.19.81

• Mattia Lepori Simon Schmid Joshua P. Barham Fakultät für Chemie und Pharmazie, Universität Regensburg, Universitatsstraße 31, 93040 Regensburg, Germany 10.3762/bjoc.19.81 Abstract Photoredox catalysis (PRC) is a cutting-edge frontier for single electron-transfer (SET) reactions, enabling the

• radicals that often provide access to new dimensions of synthetic chemical space, the field of single electron transfer (SET) in organic synthesis has expanded considerably in the past two decades. Among this area, photoredox catalysis (PRC) is highly attractive due to its abilities i) to generate reactive

Photoredox catalysis enabling decarboxylative radical cyclization of γ,γ-dimethylallyltryptophan (DMAT) derivatives: formal synthesis of 6,7-secoagroclavine

• Alessio Regni,
• Francesca Bartoccini and
• Giovanni Piersanti

Beilstein J. Org. Chem. 2023, 19, 918–927, doi:10.3762/bjoc.19.70

• manner due to their intrinsic mildness and broad substrate compatibility [16][17][18][19][20]. This transformative synthetic tool often utilizes direct single-electron transfer (SET) between an electronically excited photoredox catalyst and an organic substrate, resulting in oxidation or reduction, to

Sulfate radical anion-induced benzylic oxidation of N-(arylsulfonyl)benzylamines to N-arylsulfonylimines

• Joydev K. Laha,
• Pankaj Gupta and
• Amitava Hazra

Beilstein J. Org. Chem. 2023, 19, 771–777, doi:10.3762/bjoc.19.57

• single electron transfer (SET), is proposed to be involved in the plausible reaction mechanism. Keywords: arylsulfonylimine; benzylic oxidation; benzyl sulfonamide; K2S2O8; sulfate radical anion; Introduction Among various imine compounds [1], N-arylsulfonylimines are perhaps the most prominent due to

• abstraction (HAT) followed by single electron transfer (SET) enabled by the sulfate radical anion (SO4·−). Results and Discussion Initially, we investigated the reaction of N-benzenesulfonyl(benzyl)amine (1a) as a model substrate with K2S2O8 in MeCN at 80 °C for 12 h, conditions that were used earlier in our

• cleavage of the peroxy linkage under heating conditions [17]. The hydrogen atom is abstracted from the benzylic position of 1 by SO4·−, generating benzylic radical 1aa [14][15][16]. A single electron transfer (SET) could subsequently occur from 1aa to form the reactive species 1ab. Finally, the base

Direct C2–H alkylation of indoles driven by the photochemical activity of halogen-bonded complexes

• Martina Mamone,
• Giuseppe Gentile,
• Jacopo Dosso,
• Maurizio Prato and
• Giacomo Filippini

Beilstein J. Org. Chem. 2023, 19, 575–581, doi:10.3762/bjoc.19.42

• charge transfer state which results in a bathochromic shift of the absorption towards the visible range [19][20]. Upon light irradiation, the EDA complex may undergo an intramolecular single-electron-transfer (SET) process to produce a radical ion pair (D•+, A•−). To avoid the occurrence of a back

Combining the best of both worlds: radical-based divergent total synthesis

• Kyriaki Gennaiou,
• Antonios Kelesidis,
• Maria Kourgiantaki and
• Alexandros L. Zografos

Beilstein J. Org. Chem. 2023, 19, 1–26, doi:10.3762/bjoc.19.1

• led to common scaffolds 47 and diene 48 after subsequent elimination. Those molecules serve as templates for Ni-based radical-based sp3–sp2 coupling and single-electron transfer (SET)-based [3 + 2] coupling, respectively (Scheme 4). Initial attempts to realize the [3 + 2] radical coupling with CAN led

Redox-active molecules as organocatalysts for selective oxidative transformations – an unperceived organocatalysis field

• Elena R. Lopat’eva,
• Igor B. Krylov,
• Dmitry A. Lapshin and
• Alexander O. Terent’ev

Beilstein J. Org. Chem. 2022, 18, 1672–1695, doi:10.3762/bjoc.18.179

• catalyzed by ABNO-type amine-N-oxyl radicals. Hydrogen atom transfer (HAT) and single-electron transfer (SET) as basic principles of amine cation radical oxidative organocatalysis. Electrochemical quinuclidine-catalyzed oxidation involving unactivated C–H bonds. DABCO-mediated photocatalytic C–C cross

Radical cation Diels–Alder reactions of arylidene cycloalkanes

• Kaii Nakayama,
• Hidehiro Kamiya and
• Yohei Okada

Beilstein J. Org. Chem. 2022, 18, 1100–1106, doi:10.3762/bjoc.18.112

• to be much more effective in the reaction than other cycloalkanes. Since the reaction is completed with a substoichiometric amount of electricity, a radical cation chain pathway is likely to be involved. Keywords: arylidene cycloalkane; Diels–Alder reaction; radical cation; single-electron transfer

• ; spiro ring system; Introduction Single-electron transfer is one of the simplest modes for small molecule activation, employing a polarity inversion to generate radical ions which have proven to be unique reactive intermediates in the field of synthetic organic chemistry. A radical cation Diels–Alder

• reaction is a typical example of this activation mode since both the original diene and dienophile are electron-rich and thus not an effective combination of reactants [1][2][3][4][5][6][7][8][9][10][11]. Single-electron transfer makes the construction of six-membered ring systems possible. In general

Complementarity of solution and solid state mechanochemical reaction conditions demonstrated by 1,2-debromination of tricyclic imides

• Petar Štrbac and
• Davor Margetić

Beilstein J. Org. Chem. 2022, 18, 746–753, doi:10.3762/bjoc.18.75

• also found in the reaction of bicyclo[2.2.2] dibromide 42 (Scheme 3), which suggests that the mechanism may involve radical anion intermediates. This result further supports a single electron transfer (SET) and radical anion mechanism which was postulated earlier for the Zn/Ag debromination reaction

Direct C–H amination reactions of arenes with N-hydroxyphthalimides catalyzed by cuprous bromide

• Dongming Zhang,
• Bin Lv,
• Pan Gao,
• Xiaodong Jia and
• Yu Yuan

Beilstein J. Org. Chem. 2022, 18, 647–652, doi:10.3762/bjoc.18.65

• -electron transfer (SET) between CuBr and intermediate 5 forms intermediate 6, which initiates the N–O bond homolytic cleavage resulting in forming an N-centred phthalimidyl radical 7 (PhthN•) and anion 8. Meanwhile, Cu(I) is oxidized to Cu(II) in this step. Next, radical 7 attacks the benzene via radical

• obtained in moderate to high yields. According to the experimental results and our previous work [27][28], a possible reaction mechanism is given in Scheme 4. At first, NHPI combines with triethyl phosphite to form intermediate 4, which is the loss of ethanol to generate intermediate 5. Then, single

Earth-abundant 3d transition metals on the rise in catalysis

• Nikolaos Kaplaneris and
• Lutz Ackermann

Beilstein J. Org. Chem. 2022, 18, 86–88, doi:10.3762/bjoc.18.8

• underdeveloped. This lack of viable catalysis strategies involving 3d transition metals is largely due to a limited knowledge on the working mode of these metal catalysts, which often involve single-electron-transfer-based redox events. As a consequence, there is a strong demand for efficient and reliable

DABCO-promoted photocatalytic C–H functionalization of aldehydes

• Bruno Maia da Silva Santos,
• Mariana dos Santos Dupim,
• Cauê Paula de Souza,
• Thiago Messias Cardozo and
• Fernanda Gadini Finelli

Beilstein J. Org. Chem. 2021, 17, 2959–2967, doi:10.3762/bjoc.17.205

• (CF3)ppy]2(dtbbpy)PF6. SET = single-electron transfer event. Optimization of reaction conditionsa. Supporting Information Supporting Information File 324: General information, synthetic procedures, additional optimization and mechanistic results, NMR spectra and characterization of compounds and

Iron-catalyzed domino coupling reactions of π-systems

• Austin Pounder and
• William Tam

Beilstein J. Org. Chem. 2021, 17, 2848–2893, doi:10.3762/bjoc.17.196

• which will react further. However, reactions catalyzed by the Lewis-acidic character of iron salts are beyond the scope of this review. Iron also has the ability to transfer one or two electrons to a substrate. This opens the possibility for radical reactions via a single electron transfer (SET). Once

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

• state is transformed to the lowest-energy triplet MLCT state, which has a sufficient lifetime for initiating single-electron transfer. In the triplet species, the electron in the higher singly occupied molecular orbital (SOMO) is transferred from RuII* to an external acceptor (A), thereby yielding

• state CuI*Ln via rapid ISC. The excited CuI*Ln species has a lifetime to finish the chemical processes. A radical mechanism is proposed in Scheme 4. In path a (a ligand transfer cycle), CuI* is oxidized by an electrophilic reagent (haloalkane) to form CuII and the radical species R• in a single-electron

• transfer (SET) process. Subsequently, CuII undergoes ligand exchange with a nucleophilic reagent (Nu) to produce the CuII−Nu species. The reorganization of CuII–Nu is trapped by the radical intermediate R• to generate the final product (R–Nu) with concomitant regeneration of the CuI catalyst. Alternatively

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

Development of N-F fluorinating agents and their fluorinations: Historical perspective

• Teruo Umemoto,
• Yuhao Yang and
• Gerald B. Hammond

Beilstein J. Org. Chem. 2021, 17, 1752–1813, doi:10.3762/bjoc.17.123

Prins cyclization-mediated stereoselective synthesis of tetrahydropyrans and dihydropyrans: an inspection of twenty years

• Asha Budakoti,
• Pradip Kumar Mondal,
• Prachi Verma and
• Jagadish Khamrai

Beilstein J. Org. Chem. 2021, 17, 932–963, doi:10.3762/bjoc.17.77

• activation via DDQ oxidation, followed by nucleophilic attack of an unactivated olefin to obtain all-cis-trisubstituted Prins products with high stereochemical precision [111]. A single-electron transfer (SET) mechanism was proposed for the above transformation (Scheme 69). A SET from an arene or alkene to

Synthetic reactions driven by electron-donor–acceptor (EDA) complexes

• Zhonglie Yang,
• Yutong Liu,
• Kun Cao,
• Xiaobin Zhang,
• Hezhong Jiang and
• Jiahong Li

Beilstein J. Org. Chem. 2021, 17, 771–799, doi:10.3762/bjoc.17.67

• -light-induced single-electron-transfer process. 1,2-Diisocyanato-4,5-xylene (5) was able to capture the fluoroalkyl radical, eventually providing the quinoxaline derivative 7 (Scheme 3). In 2017, Fu and colleagues [20] selected 1-phenyl-2-(piperidin-1-yl)ethanone O-(2,4-dinitrophenyl)oxime (9) as

• reaction mechanism for this transformation is as follows (Scheme 6): Firstly, O-aryloxime 11 forms EDA complex 13 by action of DABCO·(SO2)2 and then undergoes light-promoted single-electron transfer, affording the 2,4-dinitrophenol anion, nitrogen radical 14, and radical 15, respectively. 1,5-HAT (hydrogen

• -alkyl moiety in 31 or N,N-dimethylaniline (30). This approach utilizes N,N-dimethylaniline (30) as electron donor and N-methylmaleimide (31) as electron acceptor to form an EDA complex, so that single-electron transfer occurs under ultraviolet-light irradiation. Subsequently, intermolecular proton

α,γ-Dioxygenated amides via tandem Brook rearrangement/radical oxygenation reactions and their application to syntheses of γ-lactams

• Mikhail K. Klychnikov,
• Radek Pohl,
• Ivana Císařová and
• Ullrich Jahn

Beilstein J. Org. Chem. 2021, 17, 688–704, doi:10.3762/bjoc.17.58

• reported. The sequence starts with a new tandem nucleophilic substitution/Brook rearrangement/single electron transfer-induced radical oxygenation furnishing orthogonally protected α,γ-dioxygenated N-allylamides with wide scope, mostly good yields, and partly good diastereo- and enantioselectivity for

• rearrangement/single electron transfer-induced radical oxygenation proceeds efficiently with silylacetamides 8a–g,j,k giving α,γ-dioxygenated amides 9a–p in good yields (cf. Table 2). This transformation represents a rare geminal C–C/C–O functionalization of the starting silylacetamides 8. However, neither the