C([O-])(=O)C.[NH4+:5].[Br:6][C:7]1[N:12]=[C:11]([O:13][CH3:14])[C:10]([N:15]([CH2:18][C:19](=O)[CH3:20])[CH:16]=O)=[CH:9][CH:8]=1.C(OCC)(=O)C.N>C(O)(=O)C>[Br:6][C:7]1[N:12]=[C:11]([O:13][CH3:14])[C:10]([N:15]2[CH:18]=[C:19]([CH3:20])[N:5]=[CH:16]2)=[CH:9][CH:8]=1
A suspension of ammonium acetate (267 g) and N-(6-bromo-2-methoxypyridin-3-yl)-N-(2-oxopropyl)formamide (199 g) in glacial acetic acid (400 mL) was stirred at 130° C. for one hour and 10 minutes. The reaction solution was brought back to room temperature. Ethyl acetate and ice water were added to the reaction solution, and the mixture was ice-cooled. Then, concentrated aqueous ammonia (500 mL) was added dropwise and then the organic layer was separated. The resulting organic layer was sequentially washed with water and brine and dried over anhydrous magnesium sulfate. Then, the organic layer was purified by short silica gel column chromatography (carrier: Wakogel™ C-200 manufactured by Wako Pure Chemical Industries, Ltd.; elution solvent: ethyl acetate). The eluted fraction was concentrated. The resulting residue was triturated with ethyl acetate and tert-butyl methyl ether and dried under reduced pressure to obtain 107.7 g of the title compound.
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