Formic Acid → Ethyl 2-[[3-(4-chlorophenyl)-1,2-benzisoxazol-6yl-]sulfinyl]-2-methylpropionate

3.0 g (8.0 mmole) of ethyl 2-[[3-(4-chlorophenyl)-1,2-benzisoxazol-6-yl]thio]-2-methylpropionate was combined in a flask with 0.91 g (1 eq.) of a 30% H2O2 solution, 10 ml of formic acid and 50 ml of dichloromethane. The mixture was briskly stirred and the reaction monitored by TLC. After 45 minutes, 1 ml more of a 30% H2O2 solution was added to consume the remaining starting material. The reaction was stopped when the TLC showed the starting material was consumed (at which point oxidation of the product to the sulfone will begin) and the reaction mixture was diluted with 3N HCl. The dichloromethane layer was separated, washed with 3N HCl, water, and a saturated salt solution, dried over sodium sulfate and evaporated to an oil. The oil was crystallized by adding methanol and the resulting solid was collected and recrystallized from methanol to yield 1.6 g (52%) of ethyl 2-[ [3-(4-chlorophenyl)-1,2-benzisoxazol-6yl-]sulfinyl]-2-methylpropionate, m.p. 89° C.