Alkoxy-sulphonium Salts

Few 1 -benzothiophene-S-oxides 218 were obtained in moderate yields by treatment of 1-arylacetylenes 219 with sulfur dioxide and benzene in the presence of antimony pentafluoride250 (equation 127). A series of cyclic sulphoxides have been prepared by hydrolysis of the corresponding alkoxy sulphonium salts 220251-254 (equation 128). Syn-sulphoxide 221 was obtained in a low yield (15-20%) in the reaction of the dianion of cyclooctatetraene 222 with thionyl chloride255 (equation 129). 

An intermediate (90) has been identified in the oxidation of a sulphide to a sulphoxide by l-chlorobenzotriazole. This contributes a further example to the growing number of putative quadricovalent sulphur intermediates involved in reactions of divalent sulphur compounds. Reaction of (90) with an alcohol in the presence of AgBp4 gives an alkoxy-sulphonium salt, while a secondary amine similarly gives an amino-... 

Cationic photoinitiators such as onium salts yield cationic species, which are capable of initiating cationic polymerization, upon irradiation. Radical cations and Br0nsted acids are generated via irreversible photofragmentation of diaryl iodonium, triaryl sulphonium, and /V-alkoxy pyridinium salts [ 13,14] as depicted in Scheme 13.3. 

---