2.8 Grams of 6-(4-chloro-1-butenyl)-3,4- dihydrocarbostyril and 2.1 g of sodium iodide were dissolved in 40 ml of dimethylformamide and stirred at 50° C. for 1 hour. To this solution were added 2.7 g of 4-(2-chloro-6-methlphenyl)piperazine and 1.5 g of triethylamine and the mixture was further stirred at 50° C. for 5 hours. The reaction mixture was concentrated under a reduced pressure to dryness to obtain a residue. To the residue were added 10N-NaOH and ether and stirred at a room temperature for 30 minutes to precipitate crystals. The crystals were separated by a silica-gel chromatography and recrystallized from ethanol-acetone-chloroform to obtain 6-{4-[4-(2-chloro-6-methlphenyl)-1-piperazinyl]-1-butenyl}-3,4-dihydrocarbostyril in colorless prism-like crystals. Yield: 2.7 g. Melting point: 179°-180° C.
