1.01 g of 4-acetyl-1-(2-pyrimidinyl)-5-methylpyrazole was dissolved in 80 ml of anhydrous ethanol. After adding 1.25 g of 1-benzylpiperazine hydrochloride and 0.45 g of paraformaldehyde, the mixture was heated under reflux for 18 hours. Further, 0.60 g of 1-benzylpiperazine hydrochloride and 0.20 g of paraformaldehyde were added and the resulting mixture was heated under reflux for additional 8 hours. After cooling, the crystals were collected by filtration and extracted with chloroform and a saturated aqueous solution of sodium hydrogencarbonate. The extract was washed with a saturated aqueous solution of sodium chloride and dried over anhydrous sodium sulfate. After evaporating the solvent, the residue thus obtained was purified by silica gel column chromatography (50 g, chloroform:methanol=50:1), converted into hydrochloride by adding a 1N hydrochloric acid/ethanol solution and then recrystallized from ethanol. Thus 742 mg of the title compound was obtained.
