A mixture of N,N-dimethylformamide (6 ml) and phosphorus oxychloride (918 mg) was stirred for 30 minutes at ambient temperature. To the mixture were added methylene chloride (6 ml) and 2-methoxyimino-2-(5-formamido-1,2,4-thiadiazol-3-yl)acetic acid (syn isomer) (1.1 g) at -15° to -10° C., followed by stirring for 30 minutes at the same temperature. A mixture of 7-amino-3-(1-methyl-1H-tetrazol-5-ylthiomethyl)-3-cephem-4-carboxylic acid (1.97 g) and trimethylsilylacetamide (6 g) in methylene chloride (60 ml) was warmed to make a clear solution. The solution was cooled to -15° C. and added to the above obtained solution. The reaction mixture was stirred for an hour at 0° C. and poured into a cold aqueous solution of sodium bicarbonate. The aqueous layer was separated, adjusted to pH 2 with 10% hydrochloric acid and extracted with ethyl acetate. The extract was dried over anhydrous magnesium sulfate and evaporated to dryness. The residue was triturated with diethyl ether to give a crude product of the title compound (2.75 g). The crude material was dissolved in an aqueous solution of sodium bicarbonate and reprecipitated with diluted hydrochloric acid to give the pure title compound (1.5 g), mp. 170° to 175° C. (dec.).
