[N-:1]=[N+:2]=[N-:3].[Na+].[CH3:5][O:6][C:7]1[CH:8]=[C:9]([C:15](=[O:23])[CH:16]=[CH:17][C:18]([O:20][CH2:21][CH3:22])=[O:19])[CH:10]=[CH:11][C:12]=1[O:13][CH3:14].N([O-])=O.[Na+].Cl>CN(C)C=O.[Fe](Cl)(Cl)Cl.O>[CH3:5][O:6][C:7]1[CH:8]=[C:9]([CH:10]=[CH:11][C:12]=1[O:13][CH3:14])[C:15]([C:16]1[NH:3][N:2]=[N:1][C:17]=1[C:18]([O:20][CH2:21][CH3:22])=[O:19])=[O:23]Iron(III) chloride (309 mg, 1.90 mmol) was added at room temperature to a solution (37.5 mL) of sodium azide (1.84 g, 28.3 mmol) in N,N-dimethylformamide. A solution (25 mL) of ethyl 4-(3,4-dimethoxyphenyl)-4-oxo-2-butenoate (2.50 g, 9.46 mmol) in N,N-dimethylformamide was then added to the mixture at 5° C. under an oxygen atmosphere. The temperature of the reaction solution was raised to room temperature before the reaction solution was stirred for 3 hr. Thereafter, ethyl 4-(3,4-dimethoxyphenyl)-4-oxo-2-butenoate (2.50 g, 9.46 mmol) was added to the reaction solution at room temperature, and the mixture was stirred for additional 4 hr. After the completion of the reaction, the reaction solution was poured into iced water, and sodium nitrite (636 mg, 9.22 mmol) was added thereto. The mixture was adjusted to pH 2 by the addition of 1 N hydrochloric acid and was extracted with ethyl acetate, and 5 wt % brine was then added. The mixture was adjusted to pH 2.0 by the addition of 1 N hydrochloric acid, followed by separation. The organic layer was dried over anhydrous sodium sulfate, and the solvent was then removed by evaporation under the reduced pressure. Toluene was added to the residue, and toluene was removed by evaporation under the reduced pressure. The resultant crystal was collected by filtration, 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 (5.08 g, 88%).
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