Synthesis of pyrrolidin-2-ones by 5-endo-trigonal radical cyclisation of N-vinyl-2,2-bis(phenylsulfanyl)acetamides

Abstract

A series of N-methyl-N-(1-substituted or 1,2-disubstituted vinyl)-2,2-bis(phenylsulfanyl)acetamides, upon treatment with tributyltin hydride in the presence of a catalytic amount of AIBN in boiling toluene, underwent smooth cyclisation in a 5-endo-trig manner to give the corresponding pyrrolidin-2-ones. In contrast, the N-(1-unsubstituted 2-phenylvinyl) congener gave predominantly the reduction product. These results imply that, for the 5-endo cyclisation to proceed effectively, the developing α-acylamino radicals in the transition state of the 5-endo cyclisation must be stabilised by an aryl or an alkyl group. An application of this method to a synthesis of (±)-continine is also described.