[CH3:1][S:2](Cl)(=[O:4])=[O:3].[C:6]([O:10][C:11]([N:13]1[CH2:17][CH2:16][C@H:15]([OH:18])[CH2:14]1)=[O:12])([CH3:9])([CH3:8])[CH3:7].N1C=CC=CC=1.C(OCC)(=O)C>ClCCl.O>[C:6]([O:10][C:11]([N:13]1[CH2:17][CH2:16][C@@H:15]([O:18][S:2]([CH3:1])(=[O:4])=[O:3])[CH2:14]1)=[O:12])([CH3:9])([CH3:7])[CH3:8]
Methanesulfonyl chloride was added to a mixture of (S)-3-hydroxypyrrolidine-1-carboxylic acid tert-butyl ester (40 g) and pyridine (17.4 g) in dichloromethane (400 mL) at 0° C. The reaction mixture was stirred at this temperature for 15 min and then heated at 50° C. for 8 h. The reaction mixture was subsequently mixed with ethyl acetate and water, and the ethyl acetate phase was washed with dil. HCl solution. The ethyl acetate phase was dried over sodium sulfate and the solvent was removed in vacuo. The (R)-3-methanesulfonyloxypyrrolidine-1-carboxylic acid tert-butyl ester obtained in this way was dissolved in pyrrolidine (18.2 mL), and the reaction mixture was heated to 100° C. The reaction mixture was then mixed with ethyl acetate and water. The ethyl acetate phase was washed several times with water. The organic phase was dried over sodium sulfate and the solvent was removed in vacuo.
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