Thietanium salts

Unusual fragmentation reactions for thietanium salts have been observed. Their analysis may reveal more information about the influence of d-orbitals in the reaction mechanisms of organosulfur compounds. Alkylation of certain thietanes leads to 5-methylthietanonium salts. The thietanium salt 193, which is formed from 2,4-dimethylthietane and (CH3)30" BF4, breaks up when treated with n-butyllithium into a reactive biradical and its resulting cyclopropane and a thioether. 

Whereas the phosphetanium (Sect. 2.2) derivatives undergo base-catalyzed hydrolysis with essentially complete retention of configuration, the reaction with the related thietanium salts proceeds with complete inversion of configuration and can be described simply as a direct nucleophilic substitution 35. As far as the author is aware, no exchange evidence of the type er countered in the acid-catalyzed hydrolysis of ethylene phosphate, has been found for the cyclic sulfate esters. Consequently despite the geometrical similarities between the cyclic sulfates and phosphates and the related hybridization of the central atoms, the situation in which a finite pentacovalent intermediate sulfur species exists has not been delineated (restricting the discussion to esters). 

Thietanium salts have been discussed previously (Sections II.5.A., B., D.-F., K., L. Section III.4.D) and they have been reviewed. Their stereochemistry has been... 

In thietans and thietan 1,1-dioxides, equatorial methyl groups or protons at C(2) are more shielded than geminal axial methyl groups, but, as in other cyclic sulphur compounds, the axial lone electron pair in thietan 1-oxides > and thietanium salts exerts a marked shielding effect on... 

Structures of thietanium tetrafluoroborate and hexachloroantimonate salts of 107, formed by anionotropic rearrangement of corresponding thiiranium salts, were obtained by X-ray crystallography and by calculation at the RHF/6-31G //RHF/6-31G level <2001HCA860>. 

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>. 

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... 

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. ... 

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