To a mixture of 1.2 g of 5-(1-piperazinyl)-3,4-dihydrocarbostyril, 1.17 g of potassium carbonate and 20 ml of DMF was added 858 mg of 3,4-dimethoxybenzyl chloride and the mixture was stirred at 70°-80° C. for 2 hours. The reaction mixture was poured into a large amount of water and extracted with chloroform. After washing with water the extract was dried over anhydrous sodium sulfate. Chloroform was distilled off and the residue was purified through silica gel column chromatography. The residue was converted to hydrochloric acid salt to give 610 mg of 5-[4-(3,4-dimethoxybenzyl)-1-piperazinyl]-3,4-dihydrocarbostyril dihydrochloride, m.p. 270°-272.5° C. (decomp.).
