One-step Oxidative Monofluorination of Electron-Deficient Sulfoxides to Access Highly Lewis Acidic Sulfur(VI) Cations

The strongly oxidizing, powerful electrophilic fluorination reagent FXe]OTf] is shown to effect direct oxidative monofluorination of sulfoxides. This one-step, chloride promoter-free methodology provides access to so far inaccessible, yet highly desirable strongly Lewis acidic fluorosulfoxonium cations from electron-deficient and/or sterically demanding sulfoxides that are shown to be practically unreactive towards the previously reported XeF₂/NEt₄Cl system. Experimental and density functional theory studies have been conducted to assess the Lewis acidities of the prepared sulfur(VI) cations. Preliminary results obtained with chiral sulfoxides provide early insights into the mechanism of these fluorination reactions.