Phosphoryl chloride (1.76 g.) and trimethylsilylacetamide (0.4 g.) were added to a stirred suspension of 2-(2-amino-4-thiazolyl)-2-ethoxyiminoacetic acid (syn isomer, 1.0 g) in tetrahydrofuran (10 ml.) below 5° C., and stirred at the same temperature for 30 minutes. N,N-Dimethylformamide (0.4 g.) was added to the solution and stirred below 5° C. for 20 minutes [Solution A]. Trimethylsilylacetamide (4.8 g.) was added to a stirred suspension of 4-nitrobenzyl 7-amino-3-chloro-3-cephem-4-carboxylate hydrochloride (1.9 g.) in tetrahydrofuran (15 ml.), and the solution was stirred at room temperature for an hour. To the solution was added the above Solution A all at once at -20° C., and the solution was stirred at 0° C. for an hour. Water (50 ml.) as added to the resultant solution at -20° C., and adjusted to pH 8.0 with an aqueous solution of sodium bicarbonate. Tetrahydrofuran (50 ml.) and a saturated aqueous solution of sodium chloride (50 ml.) were added to the solution. The organic layer was separated, washed with a saturated aqueous solution of sodium chloride and dried over magnesium sulfate. After concentrating the solution under reduced pressure, the residue was triturated with diisopropyl ether and the precipitates were collected by filtration to give 4-nitrobenzyl 7-[2-(2-amino-4-thiazolyl)-2-ethoxyiminoacetamido]-3-chloro-3-cephem-4-carboxylate (syn isomer, 2.0 g.).
