CN1CCOCC1.[CH2:8]([NH:11][C@H:12]([CH2:16][OH:17])[CH2:13][CH2:14][CH3:15])[CH2:9][CH3:10].[S:18](Cl)(Cl)=[O:19].O>ClCCl>[CH2:8]([N:11]1[CH:12]([CH2:13][CH2:14][CH3:15])[CH2:16][O:17][S@@:18]1=[O:19])[CH2:9][CH3:10]N-Methylmorpholine (27.3 mL) was added to a solution of (S)—N-propylnorvalinol (11.5 g) in dichloromethane (200 mL) under stirring at room temperature. A solution of thionyl chloride (9.32 mL) in dichloromethane (64 mL) was added dropwise to the resulting light yellow solution under ice-cooling and stirring. The resulting suspension was stirred at room temperature. Water was added to the suspension under ice-cooling and stirring, and the mixture was extracted with dichloromethane. The organic layer was washed with an aqueous 1 mol/L hydrochloric acid solution and subsequently with a saturated aqueous sodium hydrogen carbonate solution, dried over anhydrous magnesium sulfate, and then the solvent was removed by distillation under reduced pressure. The residue was dried under reduced pressure at room temperature overnight to give (S)-3,4-dipropyl-1,2,3-oxathiazolidine 2-oxide as a colorless oil (16.1 g, 79% yield, cis:trans=about 38:62 determined from the integration ratio in 1H-NMR).
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