Phosphorus tribromide → 5-(Bromomethyl)-1-methyl-3-nitro-1H-pyrazole

Participants

Reaction Conditions

Reaction Steps

A 25-mL three-necked round-bottomed flask equipped with a magnetic stirrer, nitrogen inlet and reflux condenser was purged with nitrogen and charged with 19 (1.83 g, 11.2 mmol) and chloroform (10 mL). The reaction was cooled to 0° C. using an ice bath and phosphorous tribromide (3.02 g, 11.2 mmol) was added dropwise. The cooling bath was removed and the reaction stirred at reflux for 2 h. After this time, the reaction was cooled to 0° C. and diluted with methylene chloride (100 mL). Saturated aqueous sodium bicarbonate (25 mL) was added until a pH of 8.5 was reached. The layers were separated, and the aqueous layer was extracted with methylene chloride (3×20 mL). The combined organic layers were washed with brine (30 mL), dried over sodium sulfate and concentrated under reduced pressure. The residue was purified by column chromatography to afford an 87% yield (1.66 g) of 20 as an off-white solid: mp 41-13° C.; 1H NMR (300 MHz, CDCl3) δ 6.91 (s, 1H), 4.44 (s, 2H), 4.01 (s, 3H).

Provenance & Evidence