Direct synthesis of acyl fluorides from carboxylic acids using benzothiazolium reagents

• Lilian M. Maas,
• Alex Haswell,
• Rory Hughes and
• Matthew N. Hopkinson

Beilstein J. Org. Chem. 2024, 20, 921–930, doi:10.3762/bjoc.20.82

• − to another molecule of thioester 3 thus sets off a chain process, delivering acyl fluoride 2 and regenerating the fluoride nucleophile. A series of experiments conducted with thioester 3a suggest a number of nucleophiles feasibly present in the reaction mixture can initiate the chain process [34

Mechanisms for radical reactions initiating from N-hydroxyphthalimide esters

• Carlos R. Azpilcueta-Nicolas and
• Jean-Philip Lumb

Beilstein J. Org. Chem. 2024, 20, 346–378, doi:10.3762/bjoc.20.35

• irradiation, EDA complex 74 triggered a radical chain process initiated by B–B bond cleavage, forming boryl-NHPI ester radical 75 and boryl radical 76. Subsequent decarboxylation of 75 yields carbon-centered radical 9 and boryl-phthalimide byproduct 77. Meanwhile DMA-ligated B2cat2 78 is formed upon

Visible-light-induced radical cascade cyclization: a catalyst-free synthetic approach to trifluoromethylated heterocycles

• Chuan Yang,
• Wei Shi,
• Jian Tian,
• Lin Guo,
• Yating Zhao and
• Wujiong Xia

Beilstein J. Org. Chem. 2024, 20, 118–124, doi:10.3762/bjoc.20.12

• radicals. This method allows the efficient synthesis of various indole derivatives without the need of photocatalysts or transition-metal catalysts. Mechanism experiments indicate that the process involves a radical chain process initiated by the homolysis of Umemoto's reagent. This straightforward method

• enables a rapid access to heterocycles containing a trifluoromethyl group. Keywords: cascade reaction; indole derivatives; photocatalysis; radical chain process; trifluoromethylation; Introduction Dihydropyrido[1,2-a]indolone (DHPI) skeletons are commonly found in natural products and pharmaceutical

• EDA charge transfer complex because there was no obvious EDA charge transfer band in the UV–vis spectra (Figure 2). Their indole substrate was more electron-rich in structure. The quantum yield was measured to investigate whether there was a radical chain process or not. The procedure was following a

α-(Aminomethyl)acrylates as acceptors in radical–polar crossover 1,4-additions of dialkylzincs: insights into enolate formation and trapping

• Angel Palillero-Cisneros,
• Paola G. Gordillo-Guerra,
• Fernando García-Alvarez,
• Olivier Jackowski,
• Franck Ferreira,
• Fabrice Chemla,
• Joel L. Terán and
• Alejandro Perez-Luna

Beilstein J. Org. Chem. 2023, 19, 1443–1451, doi:10.3762/bjoc.19.103

• alkylidenemalonates [9][10][11]. These reactions follow a free-radical chain process wherein alkyl radicals (R•) add across the C–C double bond of the 1,4-acceptor, activated by complexation with the dialkylzinc, to deliver an enoxyl radical that undergoes homolytic substitution at zinc (SH2) to produce a zinc

The preparation and properties of 1,1-difluorocyclopropane derivatives

• Kymbat S. Adekenova,
• Peter B. Wyatt and
• Sergazy M. Adekenov

Beilstein J. Org. Chem. 2021, 17, 245–272, doi:10.3762/bjoc.17.25

• this method was able to add at moderate temperatures to unreactive alkenes such as butyl acrylate (26) (Scheme 12). Fluoride ions can initiate a chain process, whereby TFDA undergoes desilylation which is followed by a subsequent decarboxylation, and loss of SO2 to form difluorocarbene :CF2 and F−; NaF

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

• quantifier of the efficiency of a photochemical process. The quantum yield (Φ) of a reaction is often used as a mechanistic tool to probe whether a chain reaction is active (Φ > 1) or not (Φ < 1), although it should be noted that a reaction with Φ < 1 could also still include a radical chain process with an

• hydrolysis provides the radical conjugate addition (RCA) products 55 with a quaternary stereocentre in excellent yields and enantioselectivities (21 examples, up to 99:1 er). The quantum yield was measured to be <1 (Φ = 0.4) for the iridium-catalysed reaction, suggesting that a radical chain process is not

• enantioselectivities (14 examples, up to 98:2 er). The quantum yield of the enantioselective reaction could not be ascertained due to the reaction being heterogenous, but the quantum yield for the racemic variant using an achiral base was >1 (Φ = 1.2), supporting the proposed radical chain process. While these results

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

• outcome is interesting from the sophisticated molecule late-stage functionalization viewpoint. Furthermore, the quantum yield of the reaction was measured and turned out to be 6.5. This result indicated that the mechanism of this reaction involved a short radical chain process [85]. The same year, a

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

• functional group tolerance of the method. Further, the authors carried out an interesting mechanistic study: From their observations, they ruled out a possible radical chain process (path I) because the reaction with styrene cannot be initiated by heating or through a radical initiator. In addition, the

Synthesis of polydicyclopentadiene using the Cp₂TiCl₂/Et₂AlCl catalytic system and thin-layer oxidation of the polymer in air

• Zhargolma B. Bazarova,
• Ludmila S. Soroka,
• Alex A. Lyapkov,
• Мekhman S. Yusubov and
• Francis Verpoort

Beilstein J. Org. Chem. 2019, 15, 733–745, doi:10.3762/bjoc.15.69

• chain process of PDCPD oxidation follows. Various mechanisms of chain initiation are possible, e.g., the formation of primary free radicals initiating the chain reaction of polymer oxidation (Equation 1). More often, the chain initiation step is described as a bimolecular interaction between oxygen and

• observable rate at low temperatures. In a kinetic mode, the polymer oxidation rate is limited by the kinetic steps of the chain process, indicating that oxygen is quickly transferred from the gaseous phase into a polymer (macro-diffusion) and does not limit the process rate. Otherwise, when oxygen is slowly

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

• of the iridium-based photocatalyst that triggers the radical chain process [27]. Results and Discussion Over the last decade, there has been a remarkable advance in synthetic chemistry that takes advantage of various chromophores (either metallic or organic) having visible-light charge transfer

• chain mechanism was further confirmed by calculating the quantum yield (Φ) because a chain process provides multiple equivalents of product per photon absorbed by the photocatalyst (Φ > 1). The photon flux of blue LED (λmax = 469 nm) was determined using the potassium ferrioxalate actinometer [57][58

• (Table 2, entry 11), implicating that the redox process is partially operating along with the main radical chain process. Norbornene (2m) was found reactive for degenerative transfer of xanthate 1a (Table 2, entry 12). The reaction was also applied to dienes 2n and 2o, which led the formation of

Stepwise radical cation Diels–Alder reaction via multiple pathways

• Ryo Shimizu,
• Yohei Okada and
• Kazuhiro Chiba

Beilstein J. Org. Chem. 2018, 14, 704–708, doi:10.3762/bjoc.14.59

• been developing oxidative SET-triggered cycloadditions of enol ethers by electrocatalysis [26][27][28][29][30][31][32] in lithium perchlorate/nitromethane electrolyte solution [33]. The reactions involve a radical cation chain process and are complete using a catalytic amount of electricity. During the

• -form 1Z was carried out in the presence of 2,3-dimethyl-1,3-butadiene (2), the corresponding Diels–Alder adduct 3 was obtained in excellent yield (Scheme 3). The reaction was completed using a catalytic amount of electricity and therefore should involve a radical cation chain process. Since Diels–Alder

Investigating radical cation chain processes in the electrocatalytic Diels–Alder reaction

• Yasushi Imada,
• Yohei Okada and
• Kazuhiro Chiba

Beilstein J. Org. Chem. 2018, 14, 642–647, doi:10.3762/bjoc.14.51

• efficiency of up to 8000%. The reaction monitoring profiles showed sigmoidal curves with induction periods, suggesting the involvement of intermediate(s) in the rate determining step. Keywords: chain process; Diels–Alder reaction; electrocatalytic; radical cation; single electron transfer; Introduction

• ][11][12] are the most straightforward approaches to induce SET processes. Since the pioneering work by Ledwith [13][14][15][16][17], a chain process involving radical ions has constituted a unique mechanism for this class of reactions, which also has the potential for contributing to effective

• . The desired Diels–Alder adduct 3 was obtained in 98% yield with less than 0.1 F/mol of electricity, suggesting that the current efficiency was up to 980%. The key step in the chain process should be the bulk SET between the starting trans-anethole (1) and the aromatic radical cation (3·+), triggering

CF₃SO₂X (X = Na, Cl) as reagents for trifluoromethylation, trifluoromethylsulfenyl-, -sulfinyl- and -sulfonylation and chlorination. Part 2: Use of CF₃SO₂Cl

• Hélène Chachignon,
• Hélène Guyon and
• Dominique Cahard

Beilstein J. Org. Chem. 2017, 13, 2800–2818, doi:10.3762/bjoc.13.273

• additional step of intramolecular cyclisation. An alternative radical chain process was also considered this time, involving notably the reaction of radical 28 with CF3SO2Cl to produce CF3• and intermediate 29. Csp2–CF3 bond-forming reactions Trifluoromethylation of arenes and heteroarenes: The pioneering

CF₃SO₂X (X = Na, Cl) as reagents for trifluoromethylation, trifluoromethylsulfenyl-, -sulfinyl- and -sulfonylation. Part 1: Use of CF₃SO₂Na

• Hélène Guyon,
• Hélène Chachignon and
• Dominique Cahard

Beilstein J. Org. Chem. 2017, 13, 2764–2799, doi:10.3762/bjoc.13.272

• using 18O2; no reaction occurred under N2 instead of O2; K2S2O8 rather than O2 served as initiator; the radical CF3SO2• could either extrude SO2 to CF3• or react with O2 to re-initiate the radical chain process (Scheme 7). Vinyl azides were used by Liu and co-workers as precursors of α

Electron-transfer-initiated benzoin- and Stetter-like reactions in packed-bed reactors for process intensification

• Anna Zaghi,
• Daniele Ragno,
• Graziano Di Carmine,
• Carmela De Risi,
• Olga Bortolini,
• Pier Paolo Giovannini,
• Giancarlo Fantin and
• Alessandro Massi

Beilstein J. Org. Chem. 2016, 12, 2719–2730, doi:10.3762/bjoc.12.268

• the cyclic intermediate III through the first adduct II. Then, the final two ET from III to the α-diketone 1 affords the product 3 regenerating the dianion I ready for a chain process. It is important to underline the beneficial effect on the reaction outcome and practicability of the polymer support

3α,5α-Cyclocholestan-6β-yl ethers as donors of the cholesterol moiety for the electrochemical synthesis of cholesterol glycoconjugates

• Aneta M. Tomkiel,
• Adam Biedrzycki,
• Jolanta Płoszyńska,
• Dorota Naróg,
• Andrzej Sobkowiak and
• Jacek W. Morzycki

Beilstein J. Org. Chem. 2015, 11, 162–168, doi:10.3762/bjoc.11.16

• carbocation; then the chain process occurs. The blank experiments (electrochemical reactions without the presence of sugar) were carried out to establish the approximate isomerization rates. The concentration of 3α,5α-cyclocholestan-6β-yl alkyl ether (methyl or ethyl) in the reaction mixture has fallen by

Cyclization–endoperoxidation cascade reactions of dienes mediated by a pyrylium photoredox catalyst

• Nathan J. Gesmundo and
• David A. Nicewicz

Beilstein J. Org. Chem. 2014, 10, 1272–1281, doi:10.3762/bjoc.10.128

• to form 6. Single electron reduction, either from 1• to regenerate active catalyst 1 or from another substrate equivalent in a chain process, forms the desired bicyclic endoperoxide. DFT calculations suggest that the formation of the initial distonic cation radical 5 is exothermic by approximately 3

The chemistry of amine radical cations produced by visible light photoredox catalysis

• Jie Hu,
• Jiang Wang,
• Theresa H. Nguyen and
• Nan Zheng

Beilstein J. Org. Chem. 2013, 9, 1977–2001, doi:10.3762/bjoc.9.234

• -electron oxidant via electron transfer or atom transfer. The trichloromethyl radical, which is generated by this oxidation, then abstracts a hydrogen atom of another molecule of N-aryltetrahydroisoquinoline to produce the α-amino radical 17, which once again enters the radical chain process with BrCCl3

Radical zinc-atom-transfer-based carbozincation of haloalkynes with dialkylzincs

• Fabrice Chemla,
• Florian Dulong,
• Franck Ferreira and
• Alejandro Pérez-Luna

Beilstein J. Org. Chem. 2013, 9, 236–245, doi:10.3762/bjoc.9.28

• in synthesis. Pivotal to the processes disclosed so far using alkylzinc derivatives is zinc atom radical transfer [4]. In general terms, the reaction involves a radical chain process initiated by the formation of an alkyl radical from the organozinc derivative in the presence of oxygen [5][6][7][8][9

Aromatic and heterocyclic perfluoroalkyl sulfides. Methods of preparation

• Vladimir N. Boiko

Beilstein J. Org. Chem. 2010, 6, 880–921, doi:10.3762/bjoc.6.88

• perfluoroalkylation (especially > 100% electrochemical yield) are consistent with a radical-chain process. Perfluoroalkyl iodides are better substrates than the bromides which give lower yields in these electrochemical reactions (Table 9). Such electrochemically initiated reactions are described in detail in a review

Do α-acyloxy and α-alkoxycarbonyloxy radicals fragment to form acyl and alkoxycarbonyl radicals?

• Dennis P. Curran and
• Tiffany R. Turner

Beilstein J. Org. Chem. 2006, 2, No. 10, doi:10.1186/1860-5397-2-10

• radical translocation occurs by 1,6-hydrogen transfer and the rebound cyclization is 1,6. The cascade in Figure 2 is a self-terminating, non-chain process if the radical X• does not continue on to propagate a chain in some way. Stable radicals such as X = NO2• or SO3•- and others are not expected to