Thiirenium ions rearrangement

With 2-methyl- and 2,4-dimethylthiazole, the methyl thiirenium ion (m/e 72) is obtained, which can easily lose a hydrogen radical to give the ml ell ion (confirmed by the metastable peak). This latter can rearrange by ring expansion to give the thietenyl cation whose structure was confirmed in certain spectra by the presence of a metastable peak corresponding to the decomposition of the m/e 71 ion to give the thioformyl cation m/e 45, probably by elimination of acetylene. 

Nesterenko and Staninets used quantum-chemical methods to examine the reaction of the phenylsulfenium ion (PhS ) with alkynes XCCY (X, Y = H, Me, Ph, CN) <2004TEC77>. Reaction was found to occur in two steps in general, forming first an acyclic cation 33 that could close to a thiirenium cation 34 or to a four-membered ring cation 35 (Scheme 4). The thiirenium ion 34 could rearrange to cation 35. All steps were described as reversible. 

Molecular Orbital (M.O.) studies of reaction intermediates have been reported for the rearrangement of l-propenethiol, for the addition of sulphenyl halides to ethylene (sulphurane rather than thiiranium salt as intermediate), and for similar additions to alkynes (thiirenium ions or /ff-alkylthiovinyl cations, depending upon the substituents). Electronic effects of substituents on energy levels of orbitals of... 

Thiiranium ions were proposed as intermediates in acid-catalyzed sulfur-atom transfer from sultene 29 to cyclic olefins under thermal conditions (Scheme 45). A high degree of diastereospecificity was observed during the sulfur atom transfer reaction to /ra r-cyclooctene. S-Dealkylation is facilitated by the formation of a stablilized carbocation, which may further cyclize or rearrange <1998JA4861>. Similar sulfur-atom transfer to cyclooctyne afforded a relatively stable thiirenium salt that did not undergo S-dealkylation (Section 1.06.5.2) <2002JA8316>. 

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