To a stirred solution of 2,2-dimethyl-4-(3-fluorophenyl)-5-{4-(methylthio)phenyl}-3(2H)-furanone (2.0 g, Example 166) in 50 ml dichloromethane, was added 1.5 g of m-chloroperoxybenzoic acid at 0° C. The reaction solution was stirred at the same temperature for one and half hours, after which 30 ml 5% aqueous sodium bicarbonate was added and the solution was stirred for another 10 minutes. Then the reaction mixture was concentrated in vacuo, and the resulting residue was extracted with 50 ml water and dichloromethane (30 ml×3). The organic layer was concentrated in vacuo and was purified by column chromatography (hexane/ethylacetate=1:1) to give 1.3 g of 2,2-dimethyl-4-(3-fluorophenyl)-5-{4-(methylsulfinyl)phenyl}-3(2H)-furanone. mp: 143-144° C. NMR: δ1.58 (s, 6H), 2.76(s, 3H), 7.26-7.08 (m, 3H), 7.30-7.38 (m, 1H), 7.65 (d, J=8.2 Hz, 2H), 7.80 (d, J=8.2 Hz, 2H).
