950739-21-6

104599-37-3

1203705-55-8

The reduction reaction was carried out by refluxing 3,4-dibromo-5-nitro-1H-pyrazole (69 g) through stannous chloride dihydrate (135 g) in a solvent mixture of ethyl acetate (600 mL) and ethanol (300 mL) at 110 °C for 45 min. 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, which was subsequently filtered through a bed of diatomaceous earth. The filter cake was washed with additional ethyl acetate (600 mL). The combined organic phases were washed with brine (200 mL), dried over anhydrous sodium sulfate, filtered and concentrated in vacuum to give the crude product as an orange oil. The crude product was purified by fast column chromatography (Biotage, Quad 25; eluent: dichloromethane solution in 6% ethanol) to give the final 5-bromo-1H-pyrazol-3-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).