Cyclic sulfonium salts

In their important work on the synthesis and properties of optically active chlorosulfurane (+)-177, Martin and Balthazor (195) deduced its absolute configuration by means of chemical correlations. Reaction of (+)-l 77 with silver tetrafluoroborate yields cyclic sulfonium salt 198, which was hydrolyzed without isolation under alkaline conditions to give sulfoxide (-)-(5 -180, from which (+)-177 was obtained. Assuming that the conversion (+)-l 77 -> 198 proceeds with... 

The reaction of 1,3-dibromopropane with methyl methylsulfanylmethyl sulfoxide in the presence of base gave cyclobutanone via the intermediate formation of ftve-membered cyclic sulfonium salt 6, which was finally converted to 1-methylsulfinyl-l-methylsulfanylcyclobutane (7 a) by a Stevens-type rearrangement in 70% yield which on acid hydrolysis gave cyclo-butanone.142... 

An analogous study has been carried out on ylide formation in cyclic sulfonium salts. Using the conformationally rigid systems in Table 12, relative kinetic acidities for Ho and Heq were determined. The results show that it is possible to remove one proton selectively, and thereby transfer chirality at sulfur to the neighbouring carbon atom (78JA200). As rigidity increases the differential kinetic acidity also increases but this is due not to an increase in overall acidity, rather to a decrease in lability of the axial proton in these... 

King and Tsang (22) have recently studied the relative rate of bimolecular substitution in dibenzyl ethylsulfonium salt 17 and the cyclic sulfonium fluoroborate salt 75. They found that the reaction of thiocyanate anion with salt 72 which can easily take the arrangement 70 is 8000 times faster than the corresponding reaction with the cyclic sulfonium salt 75, which is tied up in the arrangement 7U... 

Moreover, product formation was not the same. Dibenzyl ethylsulfonium salt 72 gave only benzyl ethyl sulfide (73) and benzyl thiocyanate 74, but no dibenzyl sulfide or ethyl thiocyanate. By contrast, the cyclic sulfonium salt 75 gave a mixture containing chiefly (80%) dihydroisothianaphthene (76) with an equivalent amount of ethyl thiocyanate (77) and a minor amount (20%) of the sulfide-thiocyanate 78. This work represents the first direct experimental information on the rate of bimolecular nucleophilic substitution and relative orientation of the benzene ring and the leaving group and it demonstrates clearly the importance of stereoelectronic effects in these reactions. 

A cyclic sulfonium salt undergoes a thia-Sommelet rearrangement which results in dearomatization and production of the 2-substituted tetrahydrothiopyran 471 in a diastereoselective fashion (Equation 156) <1998JA841>. 

A new approach to the synthesis of annulated sulfur heterocycles based on triflic anhydride-promoted electrophilic cyclization of the hetaryl-containing alkyl sulfides, including 1409, was elaborated <2003S1191>. The proposed method includes intermediate formation of sulfonylsulfonium salts 1410 followed by electrophilic attack on the aromatic ring (Scheme 271). Smooth demethylation of initially formed cyclic sulfonium salts 1411 by treatment with EtsN afforded a number of five- 1412 and six- 1413 membered fused sulfur heterocycles. Unexpected ring opening with formation of compound 1414 took place in the reaction of diethylamine with five-membered sulfonium salt 1411. 

The proof given in support of dianion formation does not however seem to be sufficients Nevertheless the single step process is reasonably efficient when primary alkyl halides are used but none of the dialkylated compound is produced with isopropyl iodide and benzyl bromide. 2-(o>-Haloalkyl)-l,3-di-thianes have proved to be valuable precursors of 1,3-dithianes derived from cyclic ketoncs. Haloge-nated 1,3-dithianes have been in turn prepared from 2-lithio-l,3-dithiane and stoichiometric amounts of u-chloro- or bromo-alkyl iodides or with an excess of the corresponding dichloride (Scheme 64, entry c). Use of u-bromoalkyldithianes is often impractical because of the ease with which these compounds are transformed into cyclic sulfonium salts. ... 

As in cationic surfactants, very few liquid chromatographic methods are described in the literature for characterizing sulfonium salts. In a recent paper, Anklam et al. [45] showed that five- and six-membered cyclic sulfonium salts of the following structure are easily analyzed via ion-pair chromatography. 

In case of cyclic sulfonium salts (two of the three substituents backbone-linked) the results indicate that sulfur-carbon cleavage leading to ring opening seems to prevail over expulsion of the open chain alkyl group.76... 

Mustard gas or bis-(g-chloroethyl) sulfide, (CICH2CH2)2S, is an oily liquid that was used extensively as poison gas in World War I. It is a deadly vesicant that causes blindness and numerous other effects. The active agent is actually the cyclic sulfonium salt... 

The formation of the cyclic sulfonium salt can be regarded as an internal or intramolecular Sj 2 displacement reaction. 

Write out this reaction mechanism. What mechanism does this process suggest for the subsequent reaction of the cyclic sulfonium salt with nucleophilic reagents ... 

Note that this reaction with nucleophiles is the reverse of the formation of the cyclic sulfonium salt. 

Higher conversions in thiirane polymerizations, however, proceed with chain scission transfer mechanism under the influence of BF3 (C2H5)20 [192]. This is indicated by a change in the molecular weight distribution, a bimodal character. When the reaction is complete there is a marked decrease in the average molecular weight of the polymer. When thietane polymerizes with triethyl-oxonium tetrafluoroborate initiation in methylene chloride, the reaction terminates after only limited conversion [193]. This results from reactions between the reactive chain ends (cyclic sulfonium salts) and the sulfur atoms on the polymer backbone. In propylene sulfide polymerization, however, terminations are mainly due to formations of 12-membered ring sulfonium salts from intramolecular reactions [193]. 

---