C(Cl)(=O)C(Cl)=O.CS(C)=O.[OH:11][CH2:12][C@H:13]1[CH2:17][CH2:16][N:15]([C:18]([O:20][C:21]([CH3:24])([CH3:23])[CH3:22])=[O:19])[CH2:14]1.CCN(CC)CC.C([O-])(O)=O.[Na+]>C(Cl)Cl>[CH:12]([C@H:13]1[CH2:17][CH2:16][N:15]([C:18]([O:20][C:21]([CH3:24])([CH3:23])[CH3:22])=[O:19])[CH2:14]1)=[O:11]To a solution of oxalyl chloride (22.17 g, 0.176 mol) in CH2Cl2 (200 mL) was added dropwise a solution of DMSO (20.59 g, 0.264 mol) in CH2Cl2 (50 mL) at −78° C. The mixture was stirred for 0.5 hours at this temperature. A solution of (S)-tert-butyl 3-(hydroxymethyl)pyrrolidine-1-carboxylate (11.8 g, 58.7 mmol) in CH2Cl2 (50 mL) was added dropwise to the reaction mixture at −78° C. The mixture was continued to stir for 1 hour at that temperature. Et3N (29.7 g, 0.294 mol) was added at −78° C. The resultant mixture was warmed to room temperature and stirred for 3 hours. The mixture was poured into saturated aqueous NaHCO3 and shaken. The organic layer was separated, washed twice with water, dried and evaporated to give a residue, which was purified by column chromatography (P.E./EtOAc 5:1) to give (S)-tert-butyl 3-formylpyrrolidine-1-carboxylate. 1H NMR (CDCl3, 300 MHz): δ 9.68 (d, J=1.8 Hz, 1H), 3.67-3.68 (m, 1H), 3.51-3.55 (m, 1H), 3.35-3.40 (m, 2H), 2.99-3.04 (m, 1H), 2.04-2.18 (m, 2H), 1.46 (s, 9H).
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