Sodium Hydroxide → (2S,4R)-4-methanesulfonyloxy-2-(4-methylthiosemicarbazidocarbonyl)-1-(4-nitrobenzyloxycarbonyl)pyrrolidine

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To a mixture of dimethylformamide (2.9 ml) and tetrahydrofuran (6 ml) was dropwise added phosphorus oxychloride (2.8 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- carboxy-4-methanesulfonyloxy-1-(4-nitrobenzyloxycarbonyl)pyrrolidine (9.65 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 a solution of 4-methylthiosemicarbazide (25 g) in a mixture of water (200 ml) and tetrahydrofuran (200 ml) at 0°-10° C. with stirring, keeping the pH between 8-9 with 1N aqueous sodium hydroxide. The mixture was stirred at the same condition for 2 hours. Tetrahydrofuran was evaporated under reduced pressure to give precipitates. The precipitates were collected by filtration, washed with water and diisopropyl ether successively, and dried over phosphorus pentoxide to give (2S, 4R)-4-methanesulfonyloxy -2-(4-methylthiosemicarbazidocarbonyl)-1-(4-nitrobenzyloxycarbonyl) pyrrolidine (9.61 g).

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