Construction of Benzocyclobutenes Enabled by Visible-Light-Induced Triplet Biradical Atom Transfer of Olefins.

Herein, we report a method that provides an array of benzocyclobutanol and benzocyclobutylamine derivatives with broad substrate scope and good functional group tolerance under mild reaction conditions. The reaction proceeds by engaging triplet biradical atom transfer of olefinic compounds in the activation of remote C(sp 3 )-H bonds upon visible-light irradiation. The reaction mechanism involves the generation of triplet excited state of diarylethylene derivative and subsequent HAT process, and then the further ring-closing reaction affording the product via an electrocyclization process. The plausible mechanism is supported by control and deuterium labeling experiments, kinetic analysis, and DFT calculations.