To a solution of 2-(2-aminothiazol-4-yl)-2-(Z)-trityloxyiminoacetic acid (2.87 g) in N,N-dimethylacetamide (28.7 ml) was added potassium carbonate (0.925 g) and methanesulfonyl chloride (1.04 ml) under ice-cooling. After stirring at the same temperature for 30 minutes, the mixture was added dropwise to a solution of diphenylmethyl 7β-amino-3-[(1,2,3-thiadiazol-5-yl)thio]-3-cephem-4-carboxylate (3.23 g) and bis-trimethylsilylacetamide (9.93 ml) in N,N-dimethylacetamide (32.3 ml) under ice-cooling. After being stirred at the same temperature for 45 minutes, the mixture was poured into a mixture of ice-water and ethyl acetate. The organic layer was separated, washed with water and brine, dried over magnesium sulfate, and evaporated to give diphenylmethyl 7β-[2-(2-aminothiazol-4-yl)-2-(Z)-(trityloxyimino)acetamido]-3-[(1,2,3-thiadiazol-5-yl)thio]-3-cephem-4-carboxylate (4.87 g).
