Cobalt‐Catalyzed Intramolecular Hydroacylation Involving Cyclopropane Cleavage

A simple cobalt‐diphosphine catalyst has been found to efficiently promote intramolecular cyclization of ortho ‐cyclopropylvinyl‐ and cyclopropylidenemethyl‐substituted benzaldehydes into benzocyclooctadienone and benzocycloheptadienone derivatives, respectively. This ring‐opening hydroacylation likely involves aldehyde C−H oxidative addition, olefin insertion, cyclopropane cleavage by β‐carbon elimination, and C−C bond‐forming reductive elimination, as was supported by mechanistic experiments and DFT calculations.