Light-Mediated Dual Phosphine-/Copper-Catalyzed Atom Transfer Radical Addition Reaction

Abstract

The atom transfer radical addition reaction catalyzed by triphenylphosphine and copper(I) halide is described. The reaction proceeds under irradiation with 365 nm light using a light-emitting diode and was performed in regular glassware. The proposed mechanism involves the formation of quaternary phosphonium salt, which undergoes single electron reduction by copper(I) salt via photo-induced electron transfer. The method works well for terminal alkenes and activated organic halides such as esters of bromo-and iodoacetic acid and bromoacetonitrile. gem-Difluorinated styrenes, for which atom transfer reactions are rare, also proved to be good substrates for this phosphine-/copper-catalyzed protocol.

Cu(II) Catalyzed Unsymmetrical Di-oxidation of gem-Difluoroalkenes to Generate α,α-Difluorinated-α-Phenoxyketones, an Unstudied Substructure

“…This regioselective attack of the radical to the difluorinated position is consistent with other radical functionalization reactions of alkenes. [27,28,33,[43][44][45] Trapping of radical 11 with Cu I Cl and molecular oxygen affords peroxo intermediate 12. Concerted elimination of Cu II oxide 12 might afford product 3 and Cu I Cl(OH) 13, [40,41,46,47] which could react with HCl to regenerate the active catalyst Cu II Cl2.…”

Phosphorus Compounds as Precursors and Catalysts for Radical C−C Bond‐Forming Reactions

“…Also in 2019, Dilman reported the phosphine/Cu(I) catalysed atom transfer radical addition (ATRA) reaction of bromoacetates across a variety of alkenes, forming haloalkanes 53 (Scheme 11). [34] This work is notable as it is the first example of the catalytic use of a phosphine to generate radicals from a phosphonium intermediate. This reaction proceeds via the addition of PPh 3 to bromoacetate 52 to generate the phosphonium 54 , which can form an ion pair with the Cu salt and undergo single electron transfer under irradiation at 365 nm.…”

Fluorine-Retentive Strategies for the Functionalization of gem-Difluoroalkenes

“…A Cu-catalyzed light-mediated difunctionalization reaction of gem-difluoroalkenes with alkyl bromides generated new C-C and C-Br bonds using a phosphine as a stoichiometric reagent (Scheme 34). 74 In this reaction, the authors exploited a novel mechanistic pathway to avoid harsh conditions, stoichiometric transition metals, and radical initiators typically required for this transformation. Initially, the bromide 208 and the phosphine reacted to form a phosphonium salt 210, and subsequent reaction with CuBr generated cuprate salt 211 (Scheme 34B).…”