General procedure for the synthesis of 7-bromo-5-nitro-1H-indazole from 2-bromo-6-methyl-4-nitroaniline: 2-bromo-6-methyl-4-nitroaniline (14.1 g, 61.0 mmol) was dissolved in glacial acetic acid (162 mL), and an aqueous solution of sodium nitrite (6.32 g, 91.5 mmol) was added slowly and dropwise (14 mL) under cooling in an ice bath. The dropwise addition time was controlled to be more than 10 min and the reaction temperature was kept below 25 °C. After the dropwise addition, the reaction mixture was stirred at 20 °C for 1 hour. After completion of the reaction, the reaction solution was concentrated under reduced pressure and the residue was ground with a 1:1 methanol:water mixture, the precipitate was collected by filtration and dried at 80 °C for 6 h. 7-Bromo-5-nitro-1H-indazole (10.4 g, 49% yield) was obtained as a red solid. MS (ESI): calculated value C7H4BrN3O2 241.0, measured value m/z 242 [M + H] +. 1H NMR (300 MHz, DMSO-d6) δ 8.84 (s, 1H), 8.53 (s, 1H), 8.37 (s, 1H).
