Z-Stereoselective semi-reduction of alkynes: modification of the Boland protocol

Highly Z-selective semi-reduction of alkynes has been achieved by adding TMSCl to a mixture of Zn(Cu/Ag), water, and methanol. The conjugated Z-alkenes have been prepared in high yields at ambient temperature. The formation of isomeric E-alkenes and over-reduction to alkanes were suppressed in our modified Boland reduction protocol. The methodology was extended to the preparation of Z-substituted stilbenes.