[F:1][C:2]([F:14])([F:13])[S:3]([C:6]1[CH:7]=[C:8](N)[CH:9]=[CH:10][CH:11]=1)(=[O:5])=[O:4].[ClH:15].N([O-])=O.[Na+].[S:20](=[O:22])=[O:21]>>[F:1][C:2]([F:14])([F:13])[S:3]([C:6]1[CH:7]=[C:8]([S:20]([Cl:15])(=[O:22])=[O:21])[CH:9]=[CH:10][CH:11]=1)(=[O:5])=[O:4]Under ice-cooling, thionyl chloride (4 mL) was added dropwise to water (24 mL) over 30 min. The mixture was stirred at room temperature for 12 hr to give a sulfur dioxide-containing solution. Under ice-cooling, {3-[(trifluoromethyl)sulfonyl]phenyl}amine (1.0 g) was added to concentrated hydrochloric acid (6 mL) and the mixture was stirred. An aqueous solution (2 mL) of sodium nitrite (0.34 g) was added dropwise while maintaining the inside temperature at not higher than 5° C. and the mixture was further stirred for 15 min. The mixture was gradually added at 5° C. to a mixture of the above-mentioned sulfur dioxide-containing solution added with cuprous chloride (10 mg). Under ice-cooling, the mixture was further stirred for 30 min, and extracted with ethyl acetate. The extract was dried over anhydrous magnesium sulfate, and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (eluent: hexane-ethyl acetate=9:1→7:3) to give the title compound as a pale-yellow oil (yield 1.08 g, 79%).
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