1-(4-benzoylpiperazin-1-yl) propan-1-one (13a) was synthesized according to the reported literature procedure. To a solution of 1-benzoylpiperizine (5 mmol, 1 eq.) and triethylamine (6 mmol, 1.2 eq.) in dry CH2Cl2 (10 ml) was added a solution of propionyl chloride (6 mmol, 1.2 eq.) in anhydrous CH2Cl2 (2 ml) at 0 °C under an N2 atmosphere. The reaction mixture was stirred for 4 h and slowly warmed to rt. The reaction mixture was treated with 3 M NaOH aq. (15 ml) and washed with brine (2 x 15 mL). The organic layer was dried with anhydrous MgSO4 and concentrated in vacuo. The crude product was purified by flash column chromatography (petroleum ether/ ethyl acetate) to give the product.