2-Arylmethyleneindolin-3-ones: photodimerisation to cyclobutane derivatives

Abstract

N-Alkyl-2-arylmethyleneindolin-3-ones have been shown to give rigid cyclobutane derivatives upon irradiation. These compounds were identified using analytical and spectroscopic data. Detailed n.m.r. studies have enabled the configuration and conformation of the photodimers to be established. It is suggested that the reaction may proceed via a triplet biradical intermediate. The cyclobutanes undergo thermal cycloreversion probably by a concerted [σ2_s+σ2_a] mechanism.