At 0° C., 54 mg (2.14 mmol) of sodium hydride were added a little at a time to a solution of 500 mg (1.95 mmol) of 4-(4-chlorophenyl)phthalazin-1(2H)-one [CAS Reg. No. 51334-86-2] in 7.6 ml of THF. After the evolution of gas had ended, 688 mg (1.95 mmol) of tert-butyl[4-(bromomethyl)phenyl](cyclopentyl)acetate, dissolved in 4.5 ml of DMF, were slowly added dropwise at 0° C., and the reaction solution was then stirred at room temperature overnight. Water was then added carefully to the reaction mixture. The reaction mixture was extracted three times with ethyl acetate, and the combined organic phases were washed with saturated sodium chloride solution and dried over sodium sulfate. After filtration, the solvent was removed to dryness under reduced pressure. The crude product obtained was purified by flash chromatography on silica gel (mobile phase: initially cyclohexane/ethyl acetate 3:1, then ethyl acetate). This gave 630 mg (93% pure, 1.11 mmol, 57% of theory) of a colorless solid.
