Sulfur Electrophiles as Mechanistic Probe. New Insight in the Electrophilic Additions

Thiiranium and thiirenium ions are stable intermediates that have been isolated and fully characterized. Structures of tert-butyl substituted thiiranium and thiirenium ions have been determined by room temperature single X-ray diffraction. In addition ab initio calculations at RHF/3-21G*//RHF/3-21G* level have been performed. Along with the definition of the structural parameters of these ions, the mechanism of their reactions with a series of sulfides has been investigated. We focus in this paper on the nucleophilic attack to sulfonium sulfur. The kinetic data, the molecular geometries, the shapes and energies of the frontier molecular orbitals suggest a mechanism in which the nucleophile approaches the sulfur in the ring plane along a direction parallel to the C-C ring bond. This result implies the intermediacy of a episulfuranic species.