The relative reactivity of thioethers and sulfoxides toward oxygen transfer reagents: the case of dioxiranes

In the competitive oxidation of thioethers and sulfoxides by electrophilic reagents the reactivity ratio may be small enough to cause the formation of mixtures of products. This has been studied in the reaction of dimethyldioxirane, DMD, and trifluoromethyl-methyldioxirane, TMMD. In particular TMMD oxidizes both thioethers and sulfoxides whereas DMD attacks only thioethers. By applying the logic which has been used to develop mechanistic probes based on such competitive oxidations, the unrealistic conclusion that TMMD is less electrophilic than DMD would be reached. On the contrary we show also by means of Hammett plots on substituted sulfoxides that DMD and TMMD are both electrophilic oxidants toward sulfoxides and that TMMD is less selective than DMD being a stronger oxidant.