General procedure for the synthesis of 5-bromo-4-fluoro-1H-indazole from 4-bromo-3-fluoro-2-methylaniline: to a stirred solution of 4-bromo-3-fluoro-2-methylaniline (15.0 g, 73.5 mmol) in acetic acid (200 mL) was added sodium nitrite (10 g, 147 mmol) in batches at 10 °C. The reaction mixture was stirred at room temperature for 16 hours. Upon completion of the reaction, a 50% aqueous NaOH solution was added dropwise to the reaction mixture under vigorous stirring at -10 °C until the pH reached 7-8. Subsequently, the mixture was extracted with ethyl acetate. The organic layer was dried with anhydrous sodium sulfate and concentrated under reduced pressure to give the crude product. The crude product was purified by silica gel column chromatography (eluent: 0-40% hexane solution of ethyl acetate) to afford 5-bromo-4-fluoro-1H-indazole (10 g, 63% yield) as an off-white solid.LCMS retention time was 3.03 min and the molecular ion peak MH+ 214.1H NMR (400 MHz, CDCl3) δ 10.44 (broad single peak, 1H), δ 8.14 (single peak, 1H), 7.49-7.45 (multiple peaks, 1H), 7.19 (double peak, J = 8.76Hz, 1H).
