To a mixture of dimethylformamide (5.28 ml) and tetrahydrofuran (15 ml) wasadded phosphorus oxychloride (6.6 ml) under cooling. The mixture was stirred for 30 minutes under ice-cooling. To the mixture was added a solution of 2-(2-tritylaminothiazol-4-yl)-2-(2-tetrahydropyranyloxyimino)acetic acid (syn isomer) (30.4 g) in tetrahydrofuran (300 ml) with stirring under ice-cooling. The mixture was stirred for 40 minutes at 3° to 5° C. to produce an activated acid solution. On the other hand, to a solution of a salt of 7-amino-3-(1-methyl-1-pyrrolidinio)methyl-3-cephem-4-carboxylate dihydrochloride (20 g) in tetrahydrofuran containing monotrimethylsilylacetamide (107 g) was added at once. The activated acid solution obtained above under cooling at -20° C. and the resulting mixture was stirred for 2 hours at -20° C. to -10° C. To thereaction mixture was added water. The insoluble materials were filtered offand the organic layer in the filtrate was separated. The aqueous layer was saturated with sodium chloride and extracted with ethyl acetate several times. The combined extract was washed with water, aqueous sodium bicarbonate and saturated aqueous sodium chloride successively, and dried over magnesium sulfate. The solvent was distilled off and the residue was subjected to column chromatography on silica gel (250 g) eluting with a mixture of ethyl acetate and isopropyl ether (1:3). The fractions containing the object compound were combined and concentrated under reduced pressure. The residue was triturated in diisopropyl ether to give 7-[2-(2-tritylaminothiazol-4-yl)-2-(2-tetrahydropyranyloxyimino)acetamido]-3-(1-methyl-1-pyrrolidinio)methyl-3-cephem-4-carboxylate (syn isomer) (75.0 g).
