Thiiranium and Thiirenium Ions Chemistry and Stereochemistry

The role of thiiranium and thiirenium ions in the electrophilic additions to alkenes and alkynes and the corresponding inverse reactions, are revisited also in the light of the recently reported rearrangements on some of these cations. The occurrence of SN2-Vin mechanism is discussed on the basis of the available experimental evidence and of quanto mechanical computation. Preliminary results on the reactivity of some stable thiiranium ions as a function of substitution pattern and on the enantioselective bifunctionalization of alkene via an optically active thiiranium ion are also reported.