In 15 ml of ethanol is dissolved 2.5 g of (R)-2-(2,2-dimethylpropanoyl)-1-methyl-5-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)isoindoline, and thereto are added 2.8 g of ethyl 7-bromo-1-cyclopropyl-8-difluoromethoxy-1,4-dihydro-4-oxoquinoline-3-carboxylate and 1.1 g of sodium carbonate. Subsequently, 150 mg of 10% palladium-activated carbon is added to the mixture in a nitrogen atmosphere and thereafter the resulting mixture is heated under reflux for 3 hours in the same atmosphere. The reaction mixture is cooled and thereafter added to a mixed solvent of 15 ml of water and 30 ml of acetone, and the crystals deposited are collected by filtration to obtain 3.6 g of ethyl (R)-1-cyclopropyl-8-difluoromethoxy-7-[2-(2,2-dimethylpropanoyl)-1-methyl-2,3-dihydro-1H-5-isoindolyl]-4-oxo-1,4-dihydro-3-quinolinecarboxylate.
