Isobutyl nitrite → 5-bromo-1H-indazole

A mixture of 3-amino-5-bromo-indazole, (4.60 g, 22 mmol) and ethanol (50 mL) was treated with hypophosphorous acid (50% aqueous solution, 9.6 ml, 87 mmol) and cooled to 0° C. To the reaction mixture was added isobutyl nitrite (2.6 mL, 22 mmol). The mixture was warmed to room temperature and the yellow suspension was stirred for two hours. The resulting brown suspension was treated with isobutyl nitrite (1 mL) and stirred at room temperature for one hour. The reaction was quenched with brine (100 mL) and the mixture extracted with ethyl acetate (2×100 mL). The combined organic layers were dried over magnesium sulfate, filtered and evaporated to a brown oil which was purified by chromatography using silica gel and hexane/ethyl acetate to give 5-bromo-indazole as a tan solid (1.74 g, 40%): mp 122-124° C.; MS [M+H]+ 195, 197.