Transition-metal-free oxindole synthesis: quinone–K2CO3 catalyzed intramolecular radical cyclization

Abstract

A novel and highly efficient transition-metal-free approach for the conversion of α-bromoanilides to 3,3-disubstituted oxindoles is described. This transformation is promoted by a catalytic amount of 9,10-phenanthrenequinone (PQ) together with K₂CO₃, and exhibits good functional group tolerance. Mechanistic investigations revealed that the reaction is most likely a radical process, possibly initiated by single electron transfer from complexes formed by PQ and K₂CO₃, to generate the tertiary radical intermediate.