Thietanium Ions

Thietanium Ions.—Methylation of m-2,4-dimethylthietan with trimethyl-oxonium fluoroborate gave the c/r-5 -methyIthietanium ion (49) stereo-specifically, but 2,2,4-trimethylthietan gave a mixture of the sulphonium salts (50) and (51) isomeric at sulphur. In the ion (49) and that (52) derived from /m y-2,4-dimethylthietan, the S—Me group adopted the 

Takamizawa, K. Hirai, andT. Ishiba, Chem. andPharm. Bull. (Japan), 1971,19,1022. 

Takamizawa,K. Hirai,andT.Ishiba, Chem.andPharm.Bull.(Japan), 1971,19,2009. 

8 Thietan l Oxides, Thietan 1,1-Dioxides, and Thiet 1,1-Dioxides 

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A number of papers describe the synthesis of thietane rings starting from thiirane rings. Lucchini et al. studied the different reactivities of cis and trans di-fert-butylthiiranium ions, 96a and 96b, with water <1997JOC7018>. It was demonstrated that the reaction of cis di-fert-butylthiiranium ion 96a with water led first to the formation of an open-chain alcohol 97, which, after ring closure, formed the trans di-/r y-butylthiiranium ion 96b. The trans Ai-tert-butylthiiranium ion 96b then rearranged to the thietanium ion 98 (Equation 31). 

Under the same conditions, but using only 0.7 equiv of water, the reaction of threo-2h7> afforded a mixture of erythro-264, threo-2(, and thietanium ion 267, (Equation 40). 

The /ra t-thiiranium ion, in separate experiments, reacted with water to afford /ra t-di-/-butylethene, in amounts depending on the concentration of water and the thietanium ion. The authors estimated rate constants for the reactions of both the as- and the /ra t-thiiranium ions with water at 25 °C and pointed out that the thiiranium salts are models for transition states for addition of electrophilic sulfur compounds to alkenes. A summary of the findings and their interpretation was published in 1997 <1997G177>. 

The hemideuteriated isotopomeric cations 25 and 26, obtained in equimolar amounts by addition of methylbis(methylthio)sulphonium hexachloroantimonate 27 to deuteriated olefin, E-t-butyl-t-butyl-D -ethylene 28 (equation 38), have been converted to the non-separable hemideuteriated thietanium ions 29 and 30, characterized spectroscopically. These rearrangements have been followed at 25 °C (over periods of 1-16 weeks) by... 

Neighbouring-group participation by )ff-sulphur, through thietanium ions, has been demonstrated. ... 

Similar results have been obtained by combining the living cationic polymerization of vinyl ethers and the ROP of thietane. In this case, the thietane acts as growing species stabilizer for the vinyl ether polymerization by reversible formation of an a-alkoxy-thietanium ion. This ion can, however, also be attacked at an endocyclic methylene by another thietane molecule leading to an alkyl-thietanium ion. This ion is incapable of reacting with a vinyl ether but is the active species for the thietane polymerization. Also in this case the end product is a star-shaped segmented polymer. 

Photolysis of 3,3,6,6-tetramethyl-5-acetoxy-l-thiacycloheptan-4-one (33) yields a small amount of 3,3-dimethyl-2-acetoxythietan. This thietan could be obtained in 30% yield by treatment of 3,3-dimethylthietan with lead tetraacetate in pyridine. The lack of reaction of the 5-hydroxy-derivative of (33) is explained by an electron-transfer quenching process involving a thietanium ion intermediate (34). 

Cyclodehydration of isoquinoline derivative (46) may proceed via a thietanium ion, and thermolysis of thiabicyclo-octene (47) may involve a 2-thietanone intermediate. ... 

Tricyclic thietanium ions were considered as intermediates in the photorearrangements of methylisothiazoles and in the rearrangements of dihydro-1,4-thiazihe (162). No evidence was obtained for a thietan ylide in the decomposition of sodium salts of toluene-p-sulphonylhydrazones of cyclic sulphides. ... 

The same team studied also Art-butyl-substituted thiiranium and thiirenium ions in reactions with disulfides, which led to the formation of thietanium and thietium ions, respectively. However, this paper only reported upon the kinetics of this... 

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