Copper(0) nanoparticle catalyzed Z ‐Selective Transfer Semihydrogenation of Internal Alkynes

The use of copper(0) nanoparticles in the transfer semihydrogenation of alkynes has been investigated as a lead‐free alternative to Lindlar catalysts. A stereo‐selective methodology for the hydrogenation of internal alkynes to the corresponding (Z)‐alkenes in high isolated yields (86% average) has been developed. This green and sustainable transfer hydrogenation protocol relies on non‐noble copper nanoparticles for reduction of both electron‐rich and electron‐deficient, aliphatic‐substituted and aromatic‐ substituted internal alkynes. Polyols, such as ethylene glycol and glycerol, have been proven to act as hydrogen sources, and excellent stereo‐ and chemoselectivity have been observed. Enabling technologies, such as microwave and ultrasound irradiation are shown to enhance heat and mass transfer, whether used alone or in combination, resulting in a decrease in reaction time from hours to minutes.