56.2 g of sodium carbonate are added to a solution of 72 g of 2-chloro-3-ethoxycarbonyl-6,7-difluoroquinoline and 45.1 g of N-methyl-N-(β-ethoxycarbonylethyl)amine in 750 cm3 of toluene. The suspension obtained is heated to approximately 90° C. and then stirred for 4 hours at this temperature. The reaction mixture is then cooled to approximately 20° C. and thereafter washed with 3 times 400 cm3 of water. The organic phase is concentrated to dryness under reduced pressure (20 kPa) at approximately 50° C. 94 g of 3-ethoxycarbonyl-6,7-difluoro-2-[N-methyl-N-(β-ethoxycarbonylethyl)amino]quinoline are obtained in the form of an oil, which is used without further purification for the subsequent steps.
