1203705-55-8

104599-37-3

1203705-55-8

The general procedure for the synthesis of 3-bromo-1H-pyrazol-5-amine using 3,4-dibromo-5-nitro-1H-pyrazole as starting material was as follows: 3,4-dibromo-5-nitro-1H-pyrazole (69 g) was reacted with stannous chloride dihydrate (135 g) in a mixture of solvents, ethyl acetate (600 mL) and ethanol (300 mL), under reflux for 45 min at 110 °C. Nitro reduction was carried out. Upon completion of the reaction, the yellow homogeneous reaction solution was cooled to room temperature and slowly poured into a vigorously stirred mixture of aqueous sodium bicarbonate (33 g) (200 mL) and ethyl acetate (800 mL). Diatomaceous earth (30 g) was added to the resulting slurry and filtered through a bed of diatomaceous earth. The filter cake was washed with additional ethyl acetate (600 mL). The organic phases were combined, washed with brine (200 mL), dried over anhydrous sodium sulfate, filtered and concentrated under reduced pressure to give the crude product as an orange oil. The crude product was further purified by fast column chromatography (Biotage, Quad 25; eluent: dichloromethane solution in 6% ethanol) to give 3-bromo-1H-pyrazol-5-amine as a light beige solid (13.2 g, 32% yield).1H NMR (400 MHz, DMSO-d6) δ: 5.20 (m, 3H), 11.60 (br s 1H).