[CH2:1]([NH:8][C:9]([O:11][CH2:12][CH3:13])=[O:10])[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.[F-].[Cs+].[CH3:16][O:17][CH2:18][C@H]1COC(=O)O1>CS(C)=O>[CH2:1]([N:8]1[CH2:13][C@H:12]([CH2:16][O:17][CH3:18])[O:11][C:9]1=[O:10])[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1Benzylurethane (15.0 g, 83.9 mmol) was dissolved in dimethyl sulfoxide (40 mL), and thereto were added cesium fluoride (1.16 g, 7.63 mmol) and (S)-4-methoxymethyl-1,3- dioxolan-2-one (10.0 g, 76.3 mmol, optical purity 98.4%ee), in order. The mixture was stirred for 28 hours at 140° C. under an atmosphere of argon. After filtering off the insoluble materials, the filtrate was condensed in vacuo, and the residue was purified by silica gel chromatography to give the subject (R)-3-benzyl-5-methoxymethyloxazolidin-2-one (14.1 g, yield 83.5%, optical purity 98.2%ee).
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