Sulfonium salts, alkyl diphenyl

Several examples of the alkylation of sulfur ylides are known. " " This reaction is particularly useful for the synthesis of j-alkyl diphenylsulfonium salts which cannot otherwise be prepared from diphenyl sulfide, 5-alkyl iodides and silver tetrafluoroborate, since the latter reaction usually leads to a mixture of regioisomeric sulfonium salts. Diphenylsulfonium methanide on reaction with [ C]methyl iodide allows the synthesis of [ C]isopropyl diphenyl sulfonium salt which has been used for the synthesis of [ C]-2,3-epoxysqualene (Scheme 130, entry a). This reaction unfortunately is not general... 

In addition to iodonium, sulfonium and selenonium compounds, onium salts of bromine, chlorine, arsenic, and phosphoras are also stable and can act as sources of cation radicals as well as Bronsted acids, when irradiated with light. Performance of diaryl chloronium and diaryl bromonium salts was studied by Nickers and Abu. Also, aryl ammonium and aryl phosphonium, and an alkyl aryl sulfonium salt were investigated. It appears that the general behavior of these materials is similar to diphenyl iodonium and triphenyl sulfonium salts. These are formations of singlet and triplet states followed by cleavages of the carbon-onium atom bonds and in-cage and out of cage-escape reactivity. The anions of choice appear to be boron tetrafluoride, phosphorus hexafluoride, arsenic hexafluoride, and antimony hexafluoride. 

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