[CH3:1][O:2][C:3]1[CH:17]=[C:16]([O:18][CH3:19])[CH:15]=[CH:14][C:4]=1[CH2:5][N:6]1[CH2:11][CH2:10][NH:9][C:8](=[O:12])[C:7]1=[O:13].[H-].[Na+].[Br:22][CH2:23][CH2:24]Br>CN(C)C=O>[Br:22][CH2:23][CH2:24][N:9]1[CH2:10][CH2:11][N:6]([CH2:5][C:4]2[CH:14]=[CH:15][C:16]([O:18][CH3:19])=[CH:17][C:3]=2[O:2][CH3:1])[C:7](=[O:13])[C:8]1=[O:12]In 100 ml of N,N-dimethylformamide was suspended 10 g of 1-(2,4-dimethoxybenzyl)-2,3-dioxopiperazine, and 1.67 g of sodium hydride (60%, oil) was added to the suspension, followed by stirring at 50° C. for 1 hour. Then, the reaction mixture was cooled to room temperature, after which 16.5 ml of 1,2-dibromoethane was added thereto and the resulting mixture was stirred at the same temperature for 4 hours. After the solvent was distilled off under reduced pressure, a mixed solvent of 100 ml of ethyl acetate and 60 ml of water was added to the residue and the pH was adjusted to 3 with 2N hydrochloric acid. The organic layer was separated and the aqueous layer was extracted with 50 ml of ethyl acetate. The combined organic layer was washed with 20 ml of water and then a saturated aqueous sodium chloride solution and dried over anhydrous magnesium sulfate. The solvent was distilled off under reduced pressure and the resulting residue was purified by a silica gel column chromatography (eluent; chloroform: methanol=30:1) to obtain 6.1 g of 1-(2-bromoethyl)-4-(2,4-dimethoxybenzyl)-2,3-dioxopiperazine as colorless crystals.
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