Efficient Highly Selective Synthesis of Methyl 2-(Ethynyl)alk-2(E)-enoates and 2-(1′-Chlorovinyl)alk-2(Z)-enoates from 2-(Methoxycarbonyl)-2,3-allenols

Highly regio- and stereoselective reactions of readily available 2-(methoxycarbonyl)-2,3-allenols 1 with oxalyl chloride in the presence of Et3N or DMSO afforded methyl 2-(ethynyl)alk-2(E)-enoates (E)-2 and 2-(1'-chlorovinyl)alk-2(Z)-enoates (Z)-3, respectively, in moderate to good yields.