Mechanism Reevaluation and Reaction Development in Rhodium-Catalyzed Cycloaddition of gem-Difluorinated Cyclopropanes

Transition-metal-catalyzed cycloadditions of strained carbocycles have emerged as a powerful strategy for constructing complex molecular architectures through C-C bond reorganization. We previously reported a Rh-catalyzed (3 + 2) cycloaddition of gem-difluorinated cyclopropanes (gem-DFCPs) with internal olefins, which was initially interpreted to proceed via a conventional cycloaddition mechanism. Mechanistic interrogation, through control experiments and DFT calculations, now reveals that this transformation proceeds through a previously unrecognized pathway involving dual C-C/C-F bond activation. The unusual cyclization mechanism involves fluoroallylic substitution, carbocation-mediated intramolecular cyclization, and fluoride transfer. This revised mechanistic framework not only redefines the understanding of such cycloadditions but also directly inspires the development of new reactions.