[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].N12CCCN=C1CCCCC2.[C:31]([O:35][CH3:36])(=[O:34])[CH:32]=[CH2:33]>CN(C)C=O>[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][N:9]([CH2:33][CH2:32][C:31]([O:35][CH3:36])=[O:34])[C:8](=[O:12])[C:7]1=[O:13]A mixture of 1.0 g of 1-(2,4-dimethoxybenzyl)-2,3-dioxopiperazine, 0.28 ml of 1,8-diazabicyclo[5.4.0]-undec-7-ene, 0.34 ml of methyl acrylate and 10 ml of N,N-dimethylformamide was stirred at room temperature for 12 hours. Then, the solvent was distilled off under reduced pressure, after which the resulting residue was added to a mixed solvent of 30 ml of ethyl acetate and 30 ml of water, and the pH was adjusted to 3 with 2N hydrochloric acid. The organic layer was separated and the aqueous layer was extracted with three 30-ml portions of ethyl acetate. The combined organic layer was washed with 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=20:1) to obtain 0.68 g of methyl 3-[4-(2,4-dimethoxybenzyl)-2,3-dioxopiperazin-1-yl]propionate as a colorless oil.
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