ClC(Cl)(Cl)[C:3]([N:5]=C=O)=[O:4].[C:10]([O:14][C:15]([N:17]1[CH2:21][CH2:20][C@@H:19]([OH:22])[CH2:18]1)=[O:16])([CH3:13])([CH3:12])[CH3:11]>C(Cl)Cl.CO>[C:10]([O:14][C:15]([N:17]1[CH2:21][CH2:20][C@@H:19]([O:22][C:3](=[O:4])[NH2:5])[CH2:18]1)=[O:16])([CH3:13])([CH3:11])[CH3:12]A solution of 4.52 g of trichloroacetyl isocyanate in 8 ml of methylene chloride was added to an ice-cooled solution of 3.75 g of (3R)-1-(t-butoxycarbonyl)-3-hydroxypyrrolidine in 40 ml of methylene chloride, and the mixture was stirred for 30 minutes with ice-cooling. After completion of the reaction, the solvent was stripped off from the reaction mixture and the residue was dissolved in 100 ml of methanol. The solution was stirred with 35 g of silica gel for 5 hours at 30° C., and then filtered. The filtrate was concentrated, giving 3.05 g of (3R)-1-(t-butoxycarbonyl)-3-carbamoyloxypyrrolidine.
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