[SH:1][C@H:2]1[C:7]([C:8]([O:10][CH2:11][CH3:12])=[O:9])=[CH:6][CH2:5][O:4][CH2:3]1.ClOC(C)(C)C.[Cl:19][C:20]1[CH:26]=[C:25]([F:27])[CH:24]=[CH:23][C:21]=1[NH2:22].S([O-])([O-])=O.[Na+].[Na+]>ClCCl>[Cl:19][C:20]1[CH:26]=[C:25]([F:27])[CH:24]=[CH:23][C:21]=1[NH:22][S:1][C@H:2]1[C:7]([C:8]([O:10][CH2:11][CH3:12])=[O:9])=[CH:6][CH2:5][O:4][CH2:3]1To a solution (400 mL) of ethyl (3S)-3-sulfanyl-3,6-dihydro-2H-pyran-4-carboxylate (14.5 g) in dichloromethane was added dropwise tert-butyl hypochlorite (10 mL) at −78° C. After stirring for 30 min, 2-chloro-4-fluoroaniline (23 mL) was added dropwise at −78° C. The reaction mixture was stirred for 1 hr, and the reaction was discontinued with 5% aqueous sodium sulfite solution (300 mL). After extraction with dichloromethane (300 mL), the extract was washed with water, and dried over anhydrous magnesium sulfate. After concentration under reduced pressure, the residue was subjected to silica gel column chromatography (hexane/ethyl acetate=15:1→5:1) to give the title compound as a crude product (20.0 g, 96.3% ee). This product was crystallized from diisopropyl ether/hexane (120 mL, 1:5) to give the title compound (12.3 g, 62%) as white crystals.
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