To a stirred solution of compound 233a (821 mg, 1.1 eq.) in anhydrous DMF (20 mL) at 0° C. was added NaH (241 mg, 1.1 eq.) portionwise. After the reaction mixture was stirred for 1 hr at room temperature, compound 221d (2 g, 1 eq.) was added and the mixture was stirred at 90° C. for 16 hrs. After the reaction mixture was cooled to room temperature, EtOAc was added. The organic phase was washed with HCl (2.5 N), dried over Na2SO4, filtered, and concentrated under reduced pressure. The crude material was purified by chromatography on silica gel (petroleum ether/DCM, 50/50) to give compound 234a as a white solid in 51% yield. MS (ESI, EI−) m/z=461.9 (MH−).
