Methyl 2-amino-5-bromo-3-methylbenzoate (19-S3, 10.9 g, 44.7 mmol) and potassium acetate (AcOK, 1.32 g, 13.41 mmol) were dissolved in dichloromethane (CH2Cl2, 50 mL) under nitrogen protection and cooled to 0 °C. Acetic anhydride (Ac2O, 10.6 g, 103 mmol) was added slowly and the reaction mixture was stirred at room temperature for 1 hour. Subsequently, the mixture was heated to 60 °C and tert-butyl nitrite (t-BuONO, 10.2 g, 98.3 mmol) was added. The resulting mixture was continued to be stirred at 60 °C for 4 hours. After completion of the reaction, it was cooled to room temperature, the reaction was quenched with saturated aqueous sodium bicarbonate (NaHCO3) and extracted with ethyl acetate (EtOAc). The organic layer was separated, dried over anhydrous sodium sulfate and concentrated to give the crude product. The crude product was purified by silica gel column chromatography (eluent: petroleum ether/ethyl acetate=100:0 to 10:1) to afford methyl 5-bromo-1H-indazole-7-carboxylate (19-S4, 8.0 g, 70.5% yield) as a yellow solid. lc-MS (ESI) m/z: 255 (M+H).
