After cooling down a mixture of 2,000 ml of dichloromethane and 2,000 ml of diethyl ether to a temperature of 0° C. to 5° C., 55 ml of phosphorus oxychloride and 38 ml of N,N-dimethylformamide were sequentially added dropwise thereto. At the same temperature, the solution was stirred for 30 minutes, and 100 g of (Z)-2-(2-t-butoxycarbonylprop-2-oxyimino)-2-(2-aminothiazol-4-yl)acetic acid was then added thereto, followed by further stirring the resulting solution for one hour. After cooling down the stirred solution to a temperature of −15° C. to −20° C., anhydrous hydrochloric acid was introduced at a rate of 500 ml/min. to 1,000 ml/min over one hour, followed by stirring the solution. Upon this stirring, the deprotection on the carboxy group was proceeded while beginning to deposit a solid material. The solid material was filtered, washed with 100 ml of dicholoromethane, and 100 ml of diethyl ether, in sequence, and then dried in vacuo, thereby yielding 85 g (86% yield) of the title compound as a white solid. Melting point (° C.): 153-158 (decomposition); 1NMR: (δ, DMSO-d6); 1.51(s, 6H), 7.19(s, 1H).
