Base-Promoted Stereoselective Hydrogenation of Ynamides with Sulfonyl Hydrazide to Give Z-Enamides.

A base-mediated semihydrogenation of ynamides using p-toluenesulfonyl hydrazide as an inexpensive and easy-to-handle hydrogen donor is reported. This transition-metal-free protocol avoids overhydrogenation and reduction of other functional groups, generating the thermodynamically unfavorable Z-enamides exclusively.