General procedure for the synthesis of 5-bromo-6-methyl-1H-indazole (compound A3) from 1-(5-bromo-6-methyl-1H-indazol-1-yl)ethanone: 1-(5-bromo-6-methyl-1H-indazol-1-yl)ethanone (3.90 g, 15.4 mmol) was suspended in methanol (12 mL) and 2.0 mol/L hydrochloric acid (39 mL). The mixture was stirred at 100 °C for 1 hour. After completion of the reaction, 10 mol/L aqueous potassium hydroxide (10 mL) was slowly added to the mixture under cooling in an ice bath. The precipitate was separated by filtration to afford the target compound 5-bromo-6-methyl-1H-indazole (compound A3, 3.20 g, yield: 97%) as colorless crystals. The product was analyzed by ESI-MS showing m/z: 211 [M + H]+; 1H-NMR (CDCl3) δ (ppm): 2.53 (s, 3H), 7.38 (d, J = 1.0 Hz, 1H), 7.96 (s, 1H), 7.98 (d, J = 1.0 Hz, 1H).
