Phosphorus oxychloride (1.2 g.) was added all at once to a suspension of 2-(2-amino-4-thiazolyl)-2-methoxyiminoacetic acid (syn-isomer: 1.23 g.) in ethyl acetate (12 ml.) at 5° C. and stirred at 4° to 6° C. for 30 minutes. Trimethylsilylacetamide (1.0 g.) was added to the solution and stirred at 4° to 6° C. for 30 minutes. Phosphorus oxychloride (1.2 g.) was added again to the solution and stirred for 15 minutes. And further, dimethylformamide (0.5 g.) was added all at once to the solution at 4° to 6° C. and stirred for 40 minutes to give a clear solution. On the other hand, p-nitrobenzyl 7-amino-3-cephem-4-carboxylate hydrochloride (1.9 g.) was added to a mixture of tetrahydrofuran (30 ml.) and acetone (10 ml.), and an aqueous solution (20 ml.) of sodium bicarbonate (0.6 g.) was added to the mixture. To the solution was added dropwise the solution obtained above at 0° to 5° C., pH 8.0. After stirring the mixture at -2° to 2° C., at pH 8.0 for 30 minutes, the insoluble substance was filtered out. The filtrate was extracted with ethyl acetate, and the extract was washed with a saturated aqueous solution of sodium chloride, dried over magnesium sulfate and then concentrated under reduced pressure. The residue was pulverized with diisopropyl ether to give p-nitrobenzyl 7-[2-(2-amino-4-thiazolyl)-2-methoxyiminoacetamido]-3-cephem-4-carboxylate (syn-isomer: 1.6 g.)
