2.6 Grams of 6-(1-hydroxy-3-chloropropyl)-3,4-dihydrocarbostyril and 1.8 g of sodium iodide were mixed in 60 ml of dimethylformamide and the mixture was stirred at a room temperature for 7 hours. Then 2.0 g of triethylamine and 2.5 g of 4-phenylpiperidine were added to the mixture and stirred at a room temperature for 24 hours. The reaction mixture was poured into 200 ml of 1%-sodium hydrogencarbonate aqueous solution and was extracted with chloroform. The chloroform layer was washed with water and dried, chloroform was removed by distillation. The residue thus obtained was recrystallized from ethanol to obtain 2.5 g of 6-[1-hydroxy-3-(4-phenyl-1-piperidyl)propyl]-3,4-dihydro-carbostyril in colorless plate-like crystals. Melting point: 155.5°-156.5° C.
