General procedure for the synthesis of 2,3-dimethyl-6-nitroindazole (2a) from 3-methyl-6-nitro-1H-indazole (1a, 10.00 g, 56 mmol) and dimethyl carbonate (DMC, 6.04 g, 67 mmol): first, 3-methyl-6-nitro-1H-indazole and triethylenediamine (DABCO, 6.40 g, 56 mmol) were dissolved in 100 mL of N,N-dimethylformamide (DMF). The reaction mixture was stirred at room temperature for 15 min, followed by slow dropwise addition of dimethyl carbonate. After the dropwise addition, the reaction system was heated to reflux temperature with continuous stirring for 6 hours. Upon completion of the reaction, the mixture was cooled to room temperature, 120 mL of water was added and stirred for 15 minutes, at which time a large amount of light yellow solid precipitated. The solid product was collected by filtration and dried to give 2,3-dimethyl-6-nitroindazole (2a, 8.66 g, 81.1% yield). The melting point of the product was 187~187.6 °C. 1H NMR (400 MHz, DMSO-d6) δ: 2.67 (s, 3H), 4.14 (s, 3H), 7.73 (d, J = 9.2 Hz, 1H), 7.93 (d, J = 8.8 Hz, 1H), 8.51 (s, 1H).
