General procedure for the synthesis of 7-bromo-[1,2,4]triazolo[1,5-a]pyridine from formic acid and the compound (CAS: 1202704-61-7): concentrated hydrochloric acid (3 mL) was added to a mixture of 98% formic acid (12 mL) and water (3 mL) of the compound 18, and the reaction mixture was heated and refluxed for 15 hours. Upon completion of the reaction, the mixture was concentrated under reduced pressure to half the original volume and neutralized with aqueous NaHCO3. The neutralized solution was extracted with a solvent mixture of methanol-chloroform (1:9, v/v). The organic phase was washed with water, dried over anhydrous sodium sulfate and evaporated under reduced pressure to remove the solvent. The resulting residue was recrystallized with hexane-chloroform mixed solvent to give 3.313 g of compound 19 as colorless needle-like crystals. The recrystallized mother liquor was further purified by column chromatography (eluent: methanol-chloroform, 1:19, v/v), and again recrystallized with hexane-chloroform mixed solvent to afford 977 mg of Compound 19 as colorless needle-like crystals. Total yield: 4.290 g (84%). Properties of compound 19: colorless needle-like crystals, melting point: 108-108.5 °C (hexane-CHCl3); 1H-NMR (300 MHz, CDCl3) δ 7.15 (dd, J = 7.2 Hz, 1H), 7.97 (d, J = 2 Hz, 1H), 8.34 (s, 1H), 8.48 (d, J = 7 Hz, 1H); LRMS m/z 197, 199 (M+, 100, 97), 156, 158 (10, 11), 91 (42), 64 (74).
![7-Bromo[1,2,4]triazolo[1,5-a]pyridine](/CAS2/GIF/1053655-66-5.gif)