[Cl:1][C:2]1[CH:3]=[CH:4][C:5]([O:15]C)=[C:6]([C:8]2[C:13](N)=[CH:12][CH:11]=[CH:10][N:9]=2)[CH:7]=1.C1COCC1.[H+].[B-](F)(F)(F)F.N([O-])=O.[Na+]>O>[Cl:1][C:2]1[CH:3]=[CH:4][C:5]2[O:15][C:13]3[C:8](=[N:9][CH:10]=[CH:11][CH:12]=3)[C:6]=2[CH:7]=1The 500 mL round-bottom flask, equipped with magnetic stirrer and reflux condenser was charged with 2-(5-chloro-2-methoxyphenyl)pyridin-3-amine (9.00 g, 39 mmol), 70 mL THF, 70 mL HBF4 (50% in water) and 40 mL H2O. Reaction mixture was cooled to −10° C., and solution of sodium nitrite (5.6 g in 20 mL water) was added dropwise. Reaction mixture was warmed gradually to room temperature and stirred overnight. The reaction mixture was diluted with 500 mL of water and extracted with ethyl acetate (4×50 mL). Organic fractions were combined, dried over sodium sulfate and evaporated, the residue was subjected to column chromatography on silica gel with hexane/ethyl acetate 9/1 mixture, providing 8-chlorobenzofuro[3,2-b]pyridine (6.00 g, colorless needles from hexane/ethyl acetate).
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