[Cl:1][C:2]1[N:7]=[CH:6][C:5](N)=[CH:4][C:3]=1[C:9]([F:12])([F:11])[F:10].[ClH:13].N([O-])=O.[Na+].[S:18](=[O:20])=[O:19]>O>[Cl:1][C:2]1[N:7]=[CH:6][C:5]([S:18]([Cl:13])(=[O:20])=[O:19])=[CH:4][C:3]=1[C:9]([F:12])([F:11])[F:10]Under ice-cooling, thionyl chloride (4 mL) was added dropwise over 20 min to water (27 mL). The mixture was stirred at room temperature for 12 hr to give a sulfur dioxide-containing solution. Separately, 6-chloro-5-(trifluoromethyl)pyridine-3-amine (1.14 g) was added to concentrated hydrochloric acid (9 mL) with stirring under ice-cooling, and concentrated hydrochloric acid (9 mL) was further added. A solution of sodium nitrite (0.44 g) in water (6 mL) was added dropwise over 10 min. The reaction mixture was gradually added at 5° C. to the above-mentioned sulfur dioxide-containing solution added with cuprous chloride (15 mg). Under ice-cooling, the mixture was further stirred for 30 min, and the precipitate was collected by filtration and washed with water. The obtained precipitate was purified by silica gel column chromatography (eluent: hexane-ethyl acetate=19:1→9:1) to give the title compound as an orange solid (yield 437 mg, 27%).
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