The general procedure for synthesizing 1-aminoindazole from indazole is as follows: with reference to Example 12, 1.33 g (10 mmol) of 1H-indazole and an appropriate amount of ethanol were added slowly to a 30 mL aqueous solution containing 2.2 g (55 mmol) of sodium hydroxide at 50°C until the reaction mixture was completely dissolved. Subsequently, the mixture was heated to 55 °C and 2.83 g (25 mmol) of hydroxylamine-O-sulfonic acid was slowly added over a period of 30 min under vigorous stirring and stirring was continued for 30 min. After completion of the reaction, the precipitate was collected by filtration and the filtrate was extracted with dichloromethane (30 mL x 2), the organic phases were combined and dried with anhydrous magnesium sulfate and concentrated under reduced pressure. The concentrate was purified by silica gel column chromatography using 10% ethyl acetate/dichloromethane as eluent. The fraction containing the target product was collected, concentrated under reduced pressure and crystallized from benzene/petroleum ether mixed solvent to give 0.63 g of the target compound 1-aminoindazole in 47% yield. The melting point of the product was 104~106 °C. The NMR hydrogen spectrum (DMSO-d6, δ) data were as follows: 5.41 (s, 2H, NH2), 6.85-7.95 (m, 4H), 8.05 (s, 1H).
