Thiiranium ions rearrangement

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>. 

In the series of dihetero-tricyclodecanes, substitutions and rearrangements involving neighboring group participation of heteroatoms (onium ions) especially of oxygen (oxonium ions) sulfur (episulfonium ions, thiiranium ions) and nitrogen (ammonium ions, aziridinium ions) as well as in one case also of selenium (epi-selenium ions), were studied on adamantanes (G1), isotwistanes (G 2), twistanes (G 2) and homotwistbrendanes (G 4). 

Both of these rearrangements may be rationalized in terms of a common intermediate thiiranium ion (Scheme 4.68). 

Intermediates in Reactimis.— Tricyclic zwitterionic thiiranium ions are suggested as intermediates in the photochemical rearrangement of thiazoles, e.g. (64) (65), (66) (67), (68). The incorporation of deuterium... 

Electrophilic attack on the sulfur atom of thiiranes by alkyl halides does not give thiiranium salts but rather products derived from attack of the halide ion on the intermediate cyclic salt (B-81MI50602). Treatment of a s-2,3-dimethylthiirane with methyl iodide yields cis-2-butene by two possible mechanisms (Scheme 31). A stereoselective isomerization of alkenes is accomplished by conversion to a thiirane of opposite stereochemistry followed by desulfurization by methyl iodide (75TL2709). Treatment of thiiranes with alkyl chlorides and bromides gives 2-chloro- or 2-bromo-ethyl sulfides (Scheme 32). Intramolecular alkylation of the sulfur atom of a thiirane may occur if the geometry is favorable the intermediate sulfonium ions are unstable to nucleophilic attack and rearrangement may occur (Scheme 33). 

Homochiral thiiranium and aziridinium ion intermediates formed by Lewis acid-induced rearrangement of l-hetero-2, 3-epoxides 97SL11. 

Payne reaction. Recent methodology takes advantage of the same anchimeric activity in optically active 2,3-epoxy sulfides and 2,3-epoxy amines (82 and 85), whereby treatment with Lewis acid induces rearrangement to the corresponding thiiranium and aziridinium ions (83 and 86) as reactive intermediates which react efficiently with a variety of nitrogen-based nucleophiles to give functionalized hydroxy sulfides (84) or hydroxy amines (87) <97SL11>. 

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... 

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