Accessing Z‐Enynes via Cobalt‐Catalyzed Propargylic Dehydrogenation

Alkenes constitute an enabling motif in organic synthesis, as they can be functionalized to form highly substituted molecules. Z ‐alkenes are generally challenging to access due to the thermodynamic preference for the formation of E ‐alkenes compared to Z ‐alkenes. Dehydrogenation methodologies to selectively form Z ‐alkenes have not yet been reported. Herein, we report a Z ‐selective, propargylic dehydrogenation that provides 1,3‐enynes through the invention of a Co‐catalyzed oxidation system. Observation of a kinetic isotope effect (KIE) revealed that deprotonation of the propargylic position is the rate limiting step. Additionally, isomerization experiments were conducted and confirmed that the observed Z ‐selectivity is a kinetic effect. A proposed stereomechanistic model for the Z ‐selectivity is included.