82419-34-9

74-96-4

82419-35-0

82419-34-9

The general procedure for the synthesis of ethyl 9,10-difluoro-3-methyl-7-oxo-3,7-dihydro-2H-[1,4]oxazino[2,3,4-ij]quinoline-6-carboxylate from ethyl bromide and fluorozinecarboxylic acid was as follows: 40 g of fluorozinecarboxylic acid was suspended in 200 mL of N,N-dimethylformamide, and ethyl bromide and 21.6 g of potassium carbonate were subsequently added to form a white suspension. The reaction mixture was stirred at 50 °C for 5 hours. Upon completion of the reaction, the mixture was cooled to room temperature and filtered to collect 60 g of white solid. The solid was dissolved in a solvent mixture of 200 mL of dichloromethane and 200 mL of methanol and stirred at 40 °C. After filtration, the undissolved solid was dissolved again in a solvent mixture of 200 mL of dichloromethane and 200 mL of methanol, stirred at 40°C and filtered. The filtrates were combined and concentrated and dried by rotary evaporator. To the dried product, 300 mL of ether was added, stirred at room temperature and filtered to obtain a white solid, i.e., target compound II.