To a solution of 3-(4-tert-butoxycarbonyl-1-piperazinyl)-2(1H)-pyrazinone (obtained in Example 48, Step 1; 0.53 g, 1.91 mmol) in THF (10 mL) was added t-BuOK (0.21 g, 1.91 mmol) and the mixture was stirred at room temperature for 10 min. The resultant mixture was added dropwise to a solution of 3-(2,4,5-trifluorophenyl)propyl methanesulfonate (0.66 g, ˜2.1 mmol; from Step 3) in THF (10 mL). The mixture was stirred at 35° C. for 3 days. Then, the solution was cooled to 0° C. and water (20 mL) and EtOAc (25 mL) were added. The aqueous phase was saturated with NaCl (2 g) and extraction performed. After separation and repeated extraction with EtOAc (15 mL) the combined organic layers were washed with brine and dried over Na2SO4. Concentration in vacuum gave 0.75 g of a yellowish oil which was purified by column chromatography on silica gel using EtOAc/n-hexane (4:1) as eluent. This gave 0.50 g (57%) of the title compound as a colorless oil. HPLC purity: 91%. 1H NMR and MS analyses support the stated structure.
