CS(C)=O.C(Cl)(=O)C(Cl)=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.C(N(CC)CC)C>ClCCl.O>[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]DMSO (1.4 mL, 19.69 mmol) in dichloromethane (2 mL) was added dropwise to a solution of oxalyl chloride (0.86 mL, 9.85 mmol) in dichloromethane (10 mL) at −78° C. After 10 min at −78° C., (R)-tert-butyl 3-(hydroxymethyl)pyrrolidine-1-carboxylate (1.8 g, 8.95 mmol) in dichloromethane (6 mL) was added dropwise. After the resulting mixture was stirred at −78° C. for 30 min, triethylamine (6.2 mL, 44.75 mmol) was added and the mixture was stirred at −78° C. for 45 min then at room temperature for 30 min. Water was added to the reaction mixture and the two layers were separated. The organic layer was washed with water, dried over sodium sulfate, filtered and the solvent removed. The crude material was purified by flash chromatography on silica gel eluting with 0 to 50% ethyl acetate/hexanes to afford 0.6 g of (R)-tert-butyl 3-formylpyrrolidine-1-carboxylate as a clear oil. 1H NMR (400 MHz, DMSO-d6) δ 9.60 (s, 1H), 3.54 (dd, 1H), 3.32-3.21 (m, 2H), 3.12 (m, 2H), 2.04 (m, 2H), 1.39 (s, 9H).
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