To a cooled (-10° C.) solution of 1.5 g (2 mM) of benzhydryl 7β-phenoxyacetamido-3-diphenylphosphoryloxy-3-cephem-4-carboxylate in 12 ml of N,N-dimethylformamide were added a solution of 177 mg (2.2 mM) of 70% sodium hydrosulfide in 8 ml of N,N-dimethylformamide and 310 mg (2.4 mM) of diisopropylethylamine, and the reaction mixture was stirred for 30 minutes. Subsequently, 330 mg (3 mM) of allyl propiolate was added at the same temperature, and the reaction mixture was stirred for 40 minutes. After the reaction, 50 ml of 0.5% hydrochloric acid was added, the mixture was extracted with 100 ml of ethyl acetate, and the extract was washed with a saturated aqueous sodium chloride solution (100 ml×2) and dried over anhydrous magnesium sulfate. The solvent was evaporated, and the residue was purified by silica gel column chromatography (eluent; ethyl acetate : n-hexane=2 : 3 to 1 : 1) to give 820 mg of benzhydryl 7β-phenoxyacetamido-3-[(Z)-2allyloxycarbonylvinylthio]-3-cephem-4-carboxylate.
