Selenonium and Telluronium Ions

A great number of trialkyl(aryl) selenonium and telluronium ions are known, and their synthesis does not require the use of strong electrophilic alkylating or arylating agents.268,269 The synthesis and transformations of triorganotellurium ions have been treated in recent reviews.270,271 However, acidic selenonium and telluronium ions can be obtained only under superacidic conditions. 

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Various sulfonium and carbosulfonium ions show remarkably enhanced reactivity upon superelectrophilic activation, similar to their oxygen analogs so do selenonium and telluronium ions. The alkylating ability of their trialkyl salts, for example, is greatly increased by protosolvation. 

Like the trialkyloxonium superelectrophiles, the salts of trimethyl sul-fonium (CH3)sS+, selenonium (CEL Se"1", and telluronium (CE Te4" ions have also been shown by Laali et al. to undergo superelectrophilic activation.41 These onium salts methylate toluene in FSChH-SbFj, but with the weaker Bronsted superacid CF3SO3H (triflic acid, //q —14.1), no methylation takes place (eq 12). 

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