[N-:1]=[N+:2]=[N-:3].[Na+].O=O.[CH3:7][O:8][C:9]1[CH:10]=[C:11]([C:17](=[O:25])[CH:18]=[CH:19][C:20]([O:22][CH2:23][CH3:24])=[O:21])[CH:12]=[CH:13][C:14]=1[O:15][CH3:16].N([O-])=O.[Na+].S(=O)(=O)(O)O>CN(C)C=O.[Cu]Cl.O>[CH3:7][O:8][C:9]1[CH:10]=[C:11]([CH:12]=[CH:13][C:14]=1[O:15][CH3:16])[C:17]([C:18]1[NH:3][N:2]=[N:1][C:19]=1[C:20]([O:22][CH2:23][CH3:24])=[O:21])=[O:25]Copper(I) chloride (190 mg, 1.91 mmol) was added at room temperature to a solution (40 mL) of sodium azide (1.84 g, 28.3 mmol) in N,N-dimethylformamide, and the air in the system was replaced by oxygen. A solution (10 mL) of ethyl 4-(3,4-dimethoxyphenyl)-4-oxo-2-butenoate (2.50 g, 9.46 mmol) in N,N-dimethylformamide was added to this mixed solution at 5° C. over a period of 30 min. The temperature of the reaction solution was raised to room temperature before the reaction solution was stirred for 3 hr. Thereafter, the reaction temperature was lowered to 5° C., and a solution (10 mL) of ethyl 4-(3,4-dimethoxyphenyl)-4-oxo-2-butenoate (2.50 g, 9.46 mmol) in N,N-dimethylformamide was added thereto. The temperature of the reaction solution was raised to room temperature before the reaction solution was stirred for 4 hr. After the completion of the reaction, the reaction solution was poured into iced water (75 mL), and sodium nitrite (636 mg, 9.22 mmol) was added thereto. The mixture was adjusted to pH 1.8 by the addition of 6 N sulfuric acid and was extracted with ethyl acetate. To the organic layer was added 5 wt % brine. The mixture was adjusted to pH 1.5 by the addition of 1 N hydrochloric acid, followed by separation. The organic layer was dried over anhydrous sodium sulfate, and the solvent was removed by evaporation under the reduced pressure. Toluene was added to the residue, and the solvent was removed by evaporation under the reduced pressure. The resultant crystal was washed with toluene and was then dried under the reduced pressure to give ethyl 5-(3,4-dimethoxybenzoyl)-1H-1,2,3-triazole-4-carboxylate (4.71 g, 81%).
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