[C:1]([NH:4][C:5]1[CH:10]=[CH:9][CH:8]=[CH:7][C:6]=1[CH2:11][C:12]([O:14][CH3:15])=[O:13])(=[O:3])[CH3:2].[N:16](OC(C)(C)C)=O>C(O)(=O)C.O.C(OC(=O)C)(=O)C>[C:1]([N:4]1[C:5]2[C:6](=[CH:7][CH:8]=[CH:9][CH:10]=2)[C:11]([C:12]([O:14][CH3:15])=[O:13])=[N:16]1)(=[O:3])[CH3:2]Methyl (2-acetamidophenyl)acetate (24.3 g, 0.12 mol) and acetic anhydride (24.3 ml, 0.26 mmol) were dissolved in acetic acid (60 ml). To the resulting solution, tert-butyl nitrite (90% purity, 18.6 ml, 0.14 mol) was added dropwise over 20 minutes under stirring at 90° C. After completion of the dropwise addition, the reaction mixture was stirred at 90° C. for further 1 hour. The reaction mixture was cooled to room temperature and then, poured in water (500 ml), followed by stirring for 1 hour. The crystals thus precipitated were collected by filtration under reduced pressure and dissolved in chloroform. The chloroform solution was washed with a saturated aqueous solution of sodium bicarbonate and saturated brine, dried over anhydrous sodium sulfate, and distilled under reduced pressure to remove the solvent, whereby methyl 1-acetylindazole-3-carboxylate (22.3 g, 85%) was obtained as a yellow solid.
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