[OH:1][C@H:2]1[CH2:6][CH2:5][N:4]([C:7]([O:9][C:10]([CH3:13])([CH3:12])[CH3:11])=[O:8])[CH2:3]1.C(N(CC)CC)C.[CH3:21][S:22](Cl)(=[O:24])=[O:23].O>C(Cl)Cl>[CH3:21][S:22]([O:1][C@H:2]1[CH2:6][CH2:5][N:4]([C:7]([O:9][C:10]([CH3:13])([CH3:12])[CH3:11])=[O:8])[CH2:3]1)(=[O:24])=[O:23]A solution of (S)-tert-butyl 3-hydroxypyrrolidine-1-carboxylate (1.0 g, 5.3 mmol) and triethylamine (2.77 mL, 20 mmol) in CH2Cl2 (20 mL) was cooled in an ice-water bath. To this, methanesulfonyl chloride (1.15 mL, 15 mmol) diluted in CH2Cl2 (10 mL) was added dropwise. The reaction was left stirring for 12 hours at room temperature. Water was added, and organic phases extracted in CH2Cl2 (3×50 mL), which were subsequently dried onto silica and purified by silica gel chromatography (50% EtOAc:Hexanes to 100% EtOAc gradient) to afford (S)-1-(tert-butoxycarbonyl)pyrrolidin-3-yl methanesulfonate (0.97 g, brown oil, 70% yield).
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