Zinc reduction of alkynes

The dissolving zinc metal reduction of ethyl phenylpropiolate to the corresponding cinnamate ester can be stereochemically controlled by changing the proton source in the reaction. The results of this study, while not fully understood, may imply that surface phenomena, coupled with a relatively slow forming equilibrium between the intermediate cis and trans anion or radical anion, competes with the rate determining protonation step in the mechanism.