Hydrogen peroxide was used for oxidation of various aryl trifluoromethyl sulfides. Trifluoroacetic acid was used as an activating solvent that enables non-catalyzed oxidation and increases selectivity for sulfoxide formation. As shown by oxidation of thianthrene TFA enhances electrophilic character of the oxidant and further oxidation of sulfoxide group is blocked. We have joined trifluoromethylthiolation of arenes using a modified Billard reagent (p-ClPhNHSCF3) with oxidation of aryl trifluoromethyl sulfides using 1.2 equiv. of 30% aqueous hydrogen peroxide and this one-pot process has superior yields than would have been obtained in a two step process.
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