General procedure for the synthesis of 2,3-dimethyl-6-amino-2H-indazole hydrochloride from 2,3-dimethyl-6-nitroindazole: 2,3-dimethyl-6-nitro-2H-indazole (1.13 g) was dissolved in 2-methoxyethyl ether (12 mL) under stirring at 0°C, and then 4.48 g of stannous chloride in 8.9 mL of concentrated hydrochloric acid was added drop by drop over a period of 5 minutes solution. After the dropwise addition was completed, the ice bath was removed and the reaction mixture continued to be stirred for 30 minutes. Subsequently, about 40 mL of diethyl ether was added to the reaction solution to induce precipitation of the product. The precipitate was separated by filtration and washed with diethyl ether to afford the yellow solid product 2,3-dimethyl-6-amino-2H-indazole hydrochloride (1.1 g, 95% yield). The structure of the product was confirmed by 1H NMR (300 MHz, DMSO-d6) and mass spectrometry (ES+): 1H NMR δ 7.77 (d, J=8.9Hz, 1H), 7.18 (s, 1H), 7.88 (m, 1H), 4.04 (s, 3H), 2.61 (s, 3H); MS (ES+, m/z) 162 (M+H).
