Seleninium salts

There have been no new reports in the literature of [4.4.0], [4.3.0], or [3.3.0] bicyclic seleninium salts. Section 8.32.2.2 of CHEC-II(1996) outlines the previous reports of such compounds. 

Keywords Heterocyclic compounds, Selenadiazoles, Selenazoles, Seleninium salts, Selenophene... 

Selenophene does not react with nucleophilic reagents by substitution or addition but only by proton transfer. Other selenaheterocycles such as 1,2- and 1,3-selenazoles, selenadiazoles, and particularly seleninium salts are susceptible to nucleophilic attack at the carbon atoms of selenaaromatic rings. 

The chemistry of seleninium salts is dominated by the electrophilicity of the cationic nucleus. The strongly electron-deficient heterocyclic ring and the annulled benzene ring are deactivated toward electrophilic attack. The nucleophiles are added to a- or y-carbons and the heterocyclic ring is dearomatized [7],... 

The best known selenaaromatic ionic systems are seleninium salts having a selenium atom placed in a six-membered ring. The synthesis and chemistry of selenopyrylium, 1-benzo-, 2-benzo- and dibenzoselenopyrylium salts have been extensively studied since the applications of these compounds in medicine and material chemistry [7, 215, 216], Very few general methods exist for the synthesis of selenopyrylium salts from acyclic precursors. The majority of the methods that are most commonly employed rely on the formation of the salts from another heterocyclic system by either an elimination process or by an aromatization. 

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