Methyl 4-amino-3-methylbenzoate (2.0 g, 12.03 mmol) was dissolved in chloroform (25 mL), and ethanoic anhydride (2.12 g, 30.07 mmol) was added slowly and dropwise at 0 °C. The reaction mixture was stirred at room temperature for 1 h. Potassium acetate (250 mg, 3.61 mmol) and isoamyl nitrite (2.23 mL, 24.06 mmol) were added sequentially. The reaction system was warmed up to 70 °C and stirred at reflux for 18 hours. Upon completion of the reaction, it was diluted by adding excess dichloromethane. The mixture was washed sequentially with saturated aqueous sodium bicarbonate, dried over anhydrous magnesium sulfate and filtered. The filtrate was concentrated under reduced pressure and the residue was purified by column chromatography to afford the intermediate methyl 1-acetyl-1H-indazole-5-carboxylate (1.2 g, 5.50 mmol).
