C(Cl)(=O)C(Cl)=O.CS(C)=O.[OH:11][C@@H:12]1[CH2:17][N:16]([C:18]([O:20][CH2:21][C:22]2[CH:27]=[CH:26][CH:25]=[CH:24][CH:23]=2)=[O:19])[C@@H:15]([CH3:28])[CH2:14][CH2:13]1.C(N(CC)CC)C>C(Cl)Cl>[CH3:28][CH:15]1[CH2:14][CH2:13][C:12](=[O:11])[CH2:17][N:16]1[C:18]([O:20][CH2:21][C:22]1[CH:27]=[CH:26][CH:25]=[CH:24][CH:23]=1)=[O:19]To a solution of oxalyl chloride (13.17 mL, 0.150 mol) in CH2Cl2 (250 mL) at −78° C. was added DMSO (14.23 mL, 0.201 mol) dropwise. The reaction was aged for 20 min at −78° C., then ±Benzyl trans-5-hydroxy-2-methylpiperidine-1-carboxylate (25.0 g, 0.100 mol) was added dropwise over 10 min and aged for an additional 10 min before triethylamine (41.9 mL, 0.301 mol) was added dropwise over 5 min at −78° C. The reaction was warmed to room temperature, then quenched with addition of half-saturated, aqueous NaHCO3 and additional CH2Cl2. The layers were separated, and the organics were dried with MgSO4 and concentrated. The crude material was purified by silica gel gradient chromatography (0-50% ethyl acetate in hexanes), providing ±benzyl 2-methyl-5-oxopiperidine-1-carboxylate.
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