2-(1H-Benzotriazol-1-yl)-1,1,3,3-tetramethyluronium tetrafluoroborate (150 mg, 0.47 mmol), diisopropylethylamine (102 mg, 0.8 mmol) and 1-(4-fluorophenyl)piperazine (65 mg, 0.47 mmol) were added sequentially at ambient temperature to a stirred solution of 3-(4-oxo-3,4-dihydrophthalazin-1-ylmethyl)benzoic acid (A) (100 mg, 0.36 mmol) in dry dimethylacetamide (1 ml), the mixture was stirred at ambient temperature for 4 hours and allowed to stand at ambient temperature for 16 hours, then it was added dropwise to stirred cold water (10 ml). After 30 minutes, the resulting solid was collected by filtration, washed with water (2×1 ml) and hexane (1 ml), dried in vacuo and purified using preparative HPLC to give 4-{3-[4-(4-fluorophenyl)piperazin-1-ylcarbonyl]benzyl}-1(2H)-phthalazinone (21)(76 mg) as a cream solid; m/z (M+H)+. 443; HPLC Purity 90%; HPLC Retention time 4.00 minutes.
