Conjugated Diene-Assisted Allylic C−H Bond Activation: Cationic Rh(I)-Catalyzed Syntheses of Polysubstituted Tetrahydropyrroles, Tetrahydrofurans, and Cyclopentanes from Ene-2-Dienes

C−H activation followed by addition to alkenes is challenging in the current C−H activation/functionalization field. We report herein an unprecedented diene-assisted transition-metal-catalyzed activation of allylic C−H bonds and their subsequent insertion into the alkene moieties of conjugated dienes. This novel C−H activation/alkene insertion reaction provides an efficient way to synthesize polysubstituted tetrahydropyrroles, tetrahydrofurans, and cyclopentanes with quaternary carbon centers. Preliminary mechanistic studies using D-labeling experiments have revealed that allylic C−H activation and alkene insertion are reversible steps, whereas the reductive elimination step, which is the final and the rate-determining step of the catalytic cycle, is irreversible.