Thiiranium Cations

Formation.—Stable thiiranium ions (63) were alleged to be formed by treatment of amides of a-methylthio- 3-chloroisobutyric acids and of 

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 

Oswald, V Synqx sium Organic Sulfur Chemistry, Lund, Sweden, June, 1972 Intemat. J. Sulfur Chem. (A), 1972, 2, 24S L. L. Stotskaya, G. A. Oreshkina, and B. A. Krentsel, V Symposium Organic Sulfur Chemistry, Lund, Sweden, June, 1972 Intemat. J. Sulfur Chem. (A), 1972,2,246 J. L. ViDa, U.S.P. 3 767 672, October 23,1973 (Chem. Abs., 1974,80,84 213)  

Hashimoto and T. Yamashita, Kobunshi Kagaku Engtish Ed, 1973,2, 0 W. Cooper, P. 

Treatment of 2,3-dimethylbut-l-ene or 2,3-dimethylbut-2-ene with methanesulphenyl bromide and silver 2,4,6-trinitrobenzenesulphonate gave the acyclic sulphonium salt (72), possibly via thiiranium salt (71). It was believed that the but-l-ene isomerized to the but-2-ene under the reaction conditions. Ethylene, cis- and traris-but-2-ene, 3,3-dimethylbut-l-ene, and 

---

Simulated annealing calculations were performed to acquire the mechanisms of thermolysis of thiirane and thiiranium cation <2002JMT71>. The AMPAC 6.55 package along with AIMl and SAMI methods were used to estimate structures, which were then used as starting points for further ab initio calculations. Critical points were confirmed by calculation of the vibrational frequencies. The primary reactions thiirane 19 —> S-f ethene, thiirane—> vinyl thiol 20, and thiirane ethanethial (thioacetaldehyde) 21 were examined for thermolysis of thiirane Scheme 1. Many secondary reactions were also examined. The simulated annealing method was predicted to be very useful in the future for the study of competing chemical reactions. 

Pasquato et al. differentiated enantiomeric thiiranium cations 72 and 73 by H NMR spectroscopy using chiral hexacoordinated phosphate anions <2002TL5517>. Results obtained with BINPHAT 74 were best. Structures of the cations and BINPHAT are shown below. 

Sometimes, a direct ion-pairing of the chiral cations and anions 8 or 15 is necessary to maximize the NMR separation of the signals [115,116]. Cationic species as different as quaternary ammonium, phosphonium, [4]heterohelice-nium, thiiranium ions, (rj -arene)manganese, ruthenium tris(diimine) have been analyzed with success (Fig. 23). 

Thiiranium ion An episulphide that is substituted on the sulphur to give a bridged sulphur cation. Thioacetal See mercaptal. 

Additions to Alkenes. The addition of phosphoranesulfenyl chlorides to alkenes is not as regioselective as similar additions of methanesulfenyl chloride or other alkyl- and arylsulfenyl chlorides where anti-Markovnikov products tend to predominate. This is due to the fact that additions of phosphoranesulfenyl chlorides proceed by an AdE2 mechanism which does not necessarily involve a thiiranium ion Intermediate, in contrast to those of C-sulfenyl chlorides.The electron-withdrawing properly of the phosphorus impairs the bridging ability of the sulfur atom sufficiently to make the intermediate possess more carbonlum ion character, with the chloride counterion more closely associated with the sulfur atom. Also, the oxygen atom attached to phosphorus may contribute to stabilization of cationic Intermediates (eq 2). ... 

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... 

---