[CH:1]([N:3]([CH2:16][C:17](=O)[CH3:18])[C:4]1[CH:13]=[CH:12][C:7]([C:8]([O:10][CH3:11])=[O:9])=[CH:6][C:5]=1[O:14][CH3:15])=O.C([O-])(=O)C.[NH4+:24].N.C(OCC)(=O)C>C(O)(=O)C>[CH3:15][O:14][C:5]1[CH:6]=[C:7]([CH:12]=[CH:13][C:4]=1[N:3]1[CH:16]=[C:17]([CH3:18])[N:24]=[CH:1]1)[C:8]([O:10][CH3:11])=[O:9]A solution of methyl 4-[formyl-(2-oxopropyl)amino]-3-methoxybenzoate (118 g) and ammonium acetate (172 g) in acetic acid (255 mL) was heated and stirred at 140° C. for one hour. After the reaction was completed, the reaction solution was neutralized with aqueous ammonia under ice-cooling. Ethyl acetate was added to the reaction solution, and the organic layer was separated. The resulting organic layer was dried over anhydrous magnesium sulfate and then filtered on a silica gel pad, and the filtrate was concentrated under reduced pressure. tert-Butyl methyl ether and heptane were added to the residue, and the precipitated solid was collected by filtration and washed with a solution of 50% tert-butyl methyl ether in heptane. The resulting solid was air-dried overnight to obtain 68.4 g of the title compound. Further, the crystallization mother liquor was concentrated under reduced pressure, and the residue was purified by silica gel column chromatography (elution solvent: heptane-ethyl acetate system) to obtain 22.3 g of the title compound.
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