Thiirenium ions

Synthesis of Aryl Thioalkynes Enabled by Electrophilic Sulfenylation of Alkynes and the Following Elimination

An unexpected deprotonative process of thiirenium ions is presented, which provides a new synthesis of aryl thioalkynes directly from terminal alkynes via the electrophilic activation of the carbon-carbon triple bonds. The conditions are well compatible with various functional-group-substituted aryl alkynes. The direct elimination from the thiirenium ion intermediate, or its tautomer, benzyl vinyl carbocation, is supported by control experiments and labeling reaction.

A G2 study of SH+ exchange reactions involving lone-pair donors and unsaturated hydrocarbons

The ligand exchange reactions between mono-adducts of the sulfenium ion ([SH-X]-) and either unsaturated hydrocarbons or lone-pair donors have been investigated computationally at the G2 level. The mono-adducts react with acetylene or ethylene to form a thiiranium or a thiirenium ion, in most cases without an overall barrier. In the reactions involving lone-pair donors, the original lone-pair donor is expelled from the [SH-X]- mono-adduct with the formation of a new mono-adduct. The reaction proceeds in this case via an intermediate di-adduct. Both the hydrocarbon and the lone-pair donor attack the mono-adduct with the relevant orbitals aligned in a near-collinear fashion, as was also the case for previously investigated reactions involving PH2+ and Cl+. The reaction energies and the binding energies of the intermediate complexes in the exchange reactions are primarily determined by the electronegativities of the lone-pair donors. The thermochemical data can be rationalized within the framework of qualitative molecular orbital theory, and the results are compared with our previous findings for the corresponding reactions involving PH2+ and Cl+.

X-ray structures and anionotropic rearrangements of Di-tert-butyl-substituted thiiranium and thiirenium ions. A structure-reactivity relationship

The X-ray structures of c-2,t-3-di-tert-butyl-r-1-methylthiiranium 8 BF(4)(-), t-2,t-3-di-tert-butyl-r-1-methylthiiranium ion 10 BF(4)(-), and 2,3-di-tert-butyl-1-methylthiirenium 11 BF(4)(-) have been determined. The DeltaG()(298) values for the rearrangements from the cis and the trans tert-butyl groups of 8 SbCl(6)(-) to thietanium ion (two intramolecular S(N)2 displacements) and for the rearrangement of 11 SbCl(6)(-) to thietium ion (an intramolecular S(N)2-Vin displacement) are linearly correlated with the strengths of the C-S breaking bonds, suggesting that the two mechanisms are, in the absence of steric hindrance, uniquely governed by the nucleofugality of the sulfonium leaving group.