Electron-shuttle catalysis enables regioselective and stereospecific dialkylation of alkynes

The dicarbofunctionalization of alkynes with unsaturated electrophiles and alkyl halides proceeding via the oxidative cyclometallation pathway offers a promising tool to synthesize multi-substituted alkenes. However, the inherent formation of cyclometallic intermediates is limited to the formation of cis products. We demonstrate here that the anti-dialkylation of alkynes with alkyl halides and unsaturated iminium is accessible via sequential radical addition promoted by cobalt electron-shuttle catalysis. This process exhibits broad substrate scope and high functional group compatibility, providing a straightforward and efficient approach to densely functionalized trans-alkenes. The newly developed facile hydrodefluorination enabled by simple LiAlH₄ further enhances the practicability of this procedure. Mechanistic studies revealed that bypassing the formation of alkenyl metal species is beneficial to obtain excellent stereoselectivity.