To a solution of phosphorus pentachloride (455 mg) in methylene chloride (15 ml) was added 2-(5-amino-1,2,4-thiadiazol-3-yl)-2-(2-cyclopenten-1-yl)oxyiminoacetic acid (syn isomer) (557 mg) at -20° C. The mixture was stirred at -20~-10° C. for 30 minutes. The resultant mixture was added to a solution of benzhydryl 7-amino-3-[(Z)-2-(3-pyridyl)vinylthio]-3-cephem-4-carboxylate (1 g) and bis(trimethylsilyl)urea (2 g) in methylene chloride (20 ml) at -20° C. The mixture was stirred at -20~-10° C. for 30 minutes. The mixture was concentrated in vacuo and the residue was dissolved in a mixture of water (100 ml), sodium bicarbonate (920 mg), ethyl acetate and tetrahydrofuran. The organic layer was separated, washed with water and a saturated aqueous solution of sodium chloride in turn, dried over magnesium sulfate, concentrated in vacuo, and the residue was triturated with diethyl ether to give benzhydryl 7-[2-(5-amino-1,2,4-thiadiazol-3-yl)-2-(2-cyclopenten-1-yl)oxyiminoacetamido]-3-[(Z)-2-(3-pyridyl)vinylthio]-3-cephem-4-carboxylate (syn isomer) (1.12 g).
