Thiophenol-Promoted Radical Chain Reduction of α-Substituted Isobutyrophenones by 1,3-Dimethyl-2-phenylbenzimidazoline

Article abstract of DOI:10.1021/jo00028a048

The reduction of α-haloacetophenones and α-halopropiophenones by 1,3-dimethyl-2-phenylbenzimidazoline (DMBI) have been reported to proceed via an electron-transfer free-radical chain mechanism.The reduction of α-haloisobutyrophenones did not proceed by the chain sequence.We mow report that initiated reductions of α-bromo- and α-chloroisobutyrophenones (IIIa,b) have been found to be promoted by the addition of thiophenol.Isobutyrophenone was formed as the major product via a free-radical chain process.During the PhSH-promoted DMBI reduction of IIIa,b a minor product, α-(phenylthio)isobutyrophenone (IV), was also formed via nucleophilic substitution.The chain propagation steps involve the efficient hydrogen atom transfers between PhCOCMe2^. and PhSH and between PhS^. and DMBI.The facile hydrogen transfer between PhS^. and DMBI was comfirmed by carrying out the radical-chain reduction of PhSSPh with DMBI.