A 1 beta-Methylcarboxylate (1) which is a requisite intermediate for t
he synthesis of the 1 beta-methylcarbapenem was obtained in an efficie
nt manner by the coupling reaction of a Z(O)-pyridylthiosilyl enol eth
er and a 4-acetoxyazetidinone derivative in the presence of ZnCl2 in C
H2Cl2. The reactive silyl enol ether was prepared by the reverse addit
ion method in high yield.