5,7-Dichloroimidazo[4,5-b]pyridine

14432-11-2

24485-01-6

General procedure for the synthesis of 5,7-dichloro-1H-imidazo[4,5-B]pyridine from 7-nitro-3H-imidazo[4,5-B]pyridine 4-oxide: 7-nitro-1H-imidazo[4,5-b]pyridine 4-oxide (2.0 g, 11.04 mmol) was added batchwise to a mixed solution of ice-bath-cooled (0 °C) phosphoryl chloride (POCl3, 30 mL , 322 mmol) and N,N-dimethylformamide (DMF, 15 mL) in a mixed solution. Subsequently, the reaction mixture was heated to 120°C and maintained for 3 hours. After completion of the reaction, it was cooled to room temperature, slowly poured into ice water and neutralized with 5 M sodium hydroxide solution. The reaction mixture was extracted with ethyl acetate (3 × 75 mL). The organic phases were combined, washed with saturated brine, dried over anhydrous sodium sulfate, and concentrated under reduced pressure to afford the crude product 5,7-dichloro-3H-imidazo[4,5-b]pyridine (1.86 g, 9.89 mmol, 90% yield), which was used directly in the next reaction without further purification. Mass spectrum (electrospray ionization) m/e 188 ([M+H]+). 1H NMR (400 MHz, methanol-d4) δ 8.45 (broad single peak, 1H), 7.46 (single peak, 1H).