tert-Butyl 1-benzyl-8-ethylamino-1,2,3,4-tetrahydro-2-oxoquinolin-3-ylcarbamate (300 mg) was dissolved in 1,2-dichloroethane (2.5 mL), and pyridine (180 mg) was added to the solution. Under cooling on ice, a solution of acetyl chloride (179 mg) in 1,2-dichloroethane (2.5 mL) was added dropwise to the mixture. The resultant mixture was stirred at room temperature for two hours, and the reaction mixture was concentrated under reduced pressure. Water was added to the thus-recovered residue, and the mixture was subjected to extraction with ethyl acetate. The organic layer was sequentially washed with 0.1N HCl, saturated aqueous sodium bicarbonate solution, and saturated aqueous sodium chloride solution, and dried over sodium sulfate. Solvent was evaporated under reduced pressure, whereby the title compound (330 mg) was yielded.
