C[S:2][C:3]1[CH:8]=[CH:7][CH:6]=[CH:5][C:4]=1[C:9]1[C:14](N)=[CH:13][CH:12]=[CH:11][N:10]=1.C1COCC1.[H+].[B-](F)(F)(F)F.N([O-])=O.[Na+]>O>[N:10]1[C:9]2[C:4]3[CH:5]=[CH:6][CH:7]=[CH:8][C:3]=3[S:2][C:14]=2[CH:13]=[CH:12][CH:11]=1The 500 mL round-bottom flask, equipped with magnetic stirrer and reflux condenser was charged with 2-(2-(methylthio)phenyl)pyridin-3-amine (8.42 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 aza-dibenzothiophene (3.5 g, colorless needles from hexane/ethyl acetate).
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