C(O[C:6]([NH:8][C@H:9]([CH2:21][OH:22])[CH2:10][C:11]([O:13][CH2:14][C:15]1[CH:20]=[CH:19][CH:18]=[CH:17][CH:16]=1)=[O:12])=[O:7])(C)(C)C.N1C=CC=CC=1.C1(C)C=CC(S(OS(C2C=CC(C)=CC=2)(=O)=O)(=O)=O)=CC=1>ClCCCl.C(Cl)Cl>[O:7]=[C:6]1[NH:8][C@@H:9]([CH2:10][C:11]([O:13][CH2:14][C:15]2[CH:16]=[CH:17][CH:18]=[CH:19][CH:20]=2)=[O:12])[CH2:21][O:22]1To a solution of (S)-benzyl 3-((tert-butoxycarbonyl)amino)-4-hydroxybutanoate (16.3 g, 52.7 mmol) and pyridine (10.65 ml, 132 mmol) in DCE (157 mL) at 0° C. was added p-toluenesulfonic anhydride (17.10 g, 52.4 mmol) in two portions over 5 min. The mixture was stirred for a few minutes, then allowed to warm to room temperature and stirred for 1 hr. The mixture was heated for 6 hr at 92° C. and then allowed to cool to room temperature. The mixture was diluted with DCM (80 mL), washed with 1N aqueous HCl solution (2×200 mL), brine (200 mL), and saturated aqueous sodium bicarbonate solution (100 mL). The organic layer was dried over sodium sulfate, filtered off and concentrated under reduced pressure. The residue was purified by column chromatography [SiO2, 220 g, EtOAc/heptane=5/95 to 75/25] to provide (S)-benzyl 2-(2-oxooxazolidin-4-yl)acetate (10.0 g) as a white solid. MS m/z 236.2 (M+H)+; Rt-0.59 min.
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