To a mixture of dimethylformamide (0.45 ml) and tetrahydrofuran (10 ml) was dropwise added phosphorus oxychloride (0.46 ml) at -5°∫5° C., and the mixture was stirred at the same temperature for 30 minutes. To the mixture was added a solution of (2S,4R)-2-(4-carboxythiazol-2-yl) -4-methanesulfonyloxy-1-(4-nitrobenzyloxycarbonyl) pyrrolidine (1.54 g) in tetrahydrofuran (20 ml) at -5°∫5° C., followed by stirring at the same temperature for 30 minutes. The mixture was dropwise added to concentrated ammonia water (15 ml) at 0°-10° C. with stirring. The mixture was stirred at the same condition for 2 hours. Tetrahydrofuran was removed under reduced pressure to give a residue, which was extracted with ethyl acetate. The organic layer was dried over magnesium sulfate and concentrated under reduced pressure to give (2S, 4R)-2-(4-carbamoylthiazol)-2-yl) -4-methanesulfonyloxy-1-(4-nitrobenzyloxycarbonyl)pyrrolidine (1.4 g).
