To a solution of compound 2 (9.27 g, 37.83 mmol) in DMSO (50 mL) was added potassium carbonate (15.68 g, 113.48 mmol). The resulting mixture was stirred at rt for 30 min. followed by addition of compound 5 (8.99 g, 45.39 mmol). The resulting mixture was heated at 120° C. O/N. The reaction mixture was diluted with EtOAc (100 mL) and washed with water (50 mL). The organic layer was dried over Na2SO4, and concentrated under reduced pressure to give crude product, which was purified by column chromatography (silica gel, 10% EtOAc in hexane) to afford the title compound 6 (5.6 g, 35%) as a pale yellow solid. 1H NMR 400 MHz (CDCl3) δ:
