[C:1]([N:4]1[C:13]2[C:8](=[CH:9][CH:10]=[CH:11][CH:12]=2)[NH:7][C:6](=[O:14])[CH2:5]1)(=[O:3])[CH3:2].[H-].[Na+].Br[CH2:18][CH:19]1[O:23][CH2:22][CH2:21][O:20]1.Cl>C(OCC)(=O)C.CN(C)C=O>[C:1]([N:4]1[C:13]2[C:8](=[CH:9][CH:10]=[CH:11][CH:12]=2)[N:7]([CH2:18][CH:19]2[O:23][CH2:22][CH2:21][O:20]2)[C:6](=[O:14])[CH2:5]1)(=[O:3])[CH3:2]To 15 mL of an N,N-dimethylformamide solution containing 957 mg of 4-acetyl-3,4-dihydro-2-oxo-1H-quinoxaline, 668 mg of sodium hydride was added, and the mixture was stirred at room temperature for 1 hour. Thereto was added 2.6 mL of 2-bromomethyl-1,3-dioxolane, and the mixture was stirred at 90° C. for 6 hours. The reaction mixture was cooled to room temperature, and then ethyl acetate and 1 mol/L hydrochloric acid were added thereto. The organic layer was separated, washed sequentially with water and an aqueous saturated sodium chloride solution and dried over anhydrous magnesium sulfate, and the solvent was removed under reduced pressure. The residue thus obtained was purified by silica gel column chromatography [silica gel; Silica gel 60 manufactured by Kanto Chemical Co., Inc., eluent; chloroform] to obtain 1.30 g of a brown oily substance, 4-acetyl-1-(1,3-dioxolan-2-ylmethyl)-2-oxo-3,4-dihydro-1H-quinoxaline.
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