One-Electron Approach for Trans-Selective Alkyne Semi-Reduction via Cobalt Catalysis
Rakesh Mondal, Lior Galmidi, Avra Tzaguy, Tal Sason, Moran Feller, Mark A. Iron, Liat Avram, Ronny Neumann, Samer Gnaim
Abstract
High Resolution Image Download MS PowerPoint Slide The diastereoselective semireduction of alkynes to alkenes is a powerful transformation in synthetic chemistry, yet catalytic methods for trans-selective (E) alkyne reduction remain limited. Herein, we introduce a fundamentally new approach for the highly selective trans-semireduction of internal alkynes, enabled by a cobalt-catalyzed electrochemical radical pathway. This method offers a broad substrate scope, accommodating alkynes with diverse electronic and steric profiles, and displays exceptional chemoselectivity and functional group tolerance. The methodology was extended to isotopically labeled trans-deuteration and demonstrated excellent chemoselectivity in substrates containing multiple alkyne motifs. Mechanistic studies, including cyclic voltammetry, UV–vis spectroelectrochemistry, and DFT calculations, support a dual catalytic cycle involving electrochemical Co–H formation and a subsequent organometallic radical pathway. Insights from this mechanism guided the development of a complementary chemical oxidative protocol, enabling access to E -alkenes from substrates that are otherwise unreactive under electroreductive conditions. This work introduces a fundamentally new and general strategy for accessing trans -alkenes from alkynes via cobalt catalysis while opening a new avenue for radical-based alkyne functionalization.