Step 3: (5-bromo-1H-indazol-3-yl)methanol (0.267 g, 1.18 mmol) was dissolved in ethyl acetate (12 mL) and manganese dioxide (1.03 g, 11.8 mmol) was added. The reaction mixture was stirred at room temperature overnight. After completion of the reaction, solid impurities were removed by diatomaceous earth filtration and the filtrate was concentrated under reduced pressure to afford 5-bromo-1H-indazole-3-carbaldehyde (0.179 g, 67% yield). The product was characterized by 1H NMR (300 MHz, DMSO-d6): δ 7.63 (dd, J = 1.5, 8.8 Hz, 1H), 7.71 (d, J = 8.8 Hz, 1H), 8.27 (d, J = 1.5 Hz, 1H), 10.18 (s, 1H), 14.37 (br s, 1H).
