General procedure for the synthesis of 6-bromo-1,2,4-triazolo[4,3-1]pyridine from 2-hydrazino-5-bromopyridine and triethyl orthoformate: to a solution of 5-bromo-2-hydrazinopyridine (7.87 g, 42 mmol) in 200 mL of diethoxymethoxyethane was added p-toluenesulfonic acid (0.30 g, 1.7 mmol), the mixture was heated to 110 °C and stirred for 20 hours. After completion of the reaction, the mixture was cooled to room temperature and concentrated under vacuum. The residue was diluted with 150 mL of water, washed with saturated aqueous NaHCO3 (40 mL), and extracted with dichloromethane (300 mL × 3). The organic phases were combined, dried with anhydrous Na2SO4, and concentrated under vacuum. Purification of the residue by fast silica gel chromatography (petroleum ether/ethyl acetate, v/v = 2/1) afforded 6-bromo-1,2,4-triazolo[4,3-1]pyridine as a yellow solid (6.60 g, 79.77% yield). Mass spectrum (ESI, cation mode) m/z: 197.9 [M + H]+; 1H NMR (600 MHz, CDCl3): δ 8.82 (s, 1H), 8.34 (s, 1H), 7.75 (d, J = 9.7 Hz, 1H), 7.36 (d, J = 9.7 Hz, 1H).
![6-BROMO-1,2,4-TRIAZOLO[4,3-1]PYRIDINE](/CAS/GIF/108281-79-4.gif)