Stereoselectivity in the Synthesis of Enol Esters from Chloromercurio Aldehydes and Acyl Chlorides

Reactions of chloromercurio aldehydes with acyl chlorides gave a variety of (Z)- and (E)-enol esters. The Z/E ratio of the enol esters is dependent on the structure of chloromercurio aldehydes but independent of that of acyl chlorides. Z-Rich enol esters were prepared by acylation of 2-chloromercurio aldehydes derived from propanal, butanal, and 2-phenylethanal, while E-rich 1-acyloxy-1,3-butadiene was obtained by acylation of (E)-4-chloromercurio-2-butenal. Reaction mechanisms for the stereoselective formation of these enol esters are discussed together with the isomer composition of starting enol acetates from which the chloromercurio aldehydes were prepared.