Acetyl chloride (18 mL) was slowly added dropwise to methanol (180 mL) at 0 °C and the reaction mixture was kept stirred at this temperature for 1 hour. Subsequently, 4-methoxy-1H-indazole-3-carboxylic acid (21.8 mmol) was added and the reaction mixture was heated to reflux for 3 hours. After completion of the reaction, the solution was concentrated to dryness under reduced pressure. The resulting residue was suspended in water and the pH was adjusted with saturated sodium bicarbonate solution to 7. Next, extraction was carried out with ethyl acetate (3 x 100 mL), the organic layers were combined, dried with anhydrous magnesium sulfate, filtered and concentrated under reduced pressure. Finally, the crude product was purified by column chromatography (eluent ratio of 2:1 petroleum ether/ethyl acetate) to afford methyl 4-methoxy-1H-indazole-3-carboxylate in 5% yield (two-step reaction) and the product was a yellow solid.
