Unpurified 4-[3,5-difluoro-4-(methylthio)-phenyl]-3-phenylfuran-2(5H)-one (8.9 g, 27 mmol) and magnesum monoperoxyphthalate hexahydrate (17.2 g, 27 mmol) were combined in a mixture of dichloromethane (200 mL) and methanol (60 mL), and stirred overnight at room temperature. The slurry was poured into water, and extracted with dichloromethane (1×200 mL, 2×50 mL). The combined extracts were washed with water and dilute sodium bicarbonate, and the aqueous sodium bicarbonate wash extracted with dichloromethane (50 mL). The combined extracts were dried with magnesium sulfate, filtered and concentrated. The residue was treated again with magnesium monoperoxyphthalate hexahydrate (8.5 g., 25 mmol), in a mixture of dichloromethane (120 mL) and methanol (30 mL), stirring overnight at room temperature. The reaction mixture was poured into water, and extracted with dichloromethane (2×200 mL). The combined extracts were washed with dilute ammonium chloride (100 mL), and dilute sodium chloride (100 mL), dried with magnesium sulfate, and concentrated to give 6.7 g yellow solids. The crude product was dissolved in dichloromethane (20 mL), and crystallized by adding a mixture of 40% ethyl acetate/60% hexanes (15 mL). The product was filtered, and the filtrate purified by silica gel chromatography using 40% ethyl acetate/60% hexanes to give a total of 5.3 g yellow solids (56%). The 4-[3,5-difluoro-4-(methylsulfonyl)phenyl]-3-phenylfuran-2(5H)-one was recrystallized from ethyl acetate to give white solids. MP 203.5-203.8° C. 1H NMR (CDCl3/400 MHz) 7.35-7.44 (m, 5H), 6.97 (d, 2H, J=9.0), 5.11 (s, 2H), 3.29 (s, 3H). ESHRMS m/z 351.0536 (M+H+, Calcd 351.0502). Anal. Calcd for C17H12F2O4S: C, 58.28; H, 3.45. Found: C, 57.69; H, 3.72.
