Selenopyrylium salts, 4-

Reactions of 2-benzoselenopyrylium salts 74 with methyl- or phenyl-hydrazine afforded the 1 -hydrazino-1 //-isoselenochromenes, while the treatment of the selenopyrylium salts 74 with anhydrous hydrazine in dry MeCN resulted in a ring transformation to give the 5/7-2,3-diazepines 75 in the one-pot reaction under mild conditions in moderate yields <2005CPB60> (Equation 9). 

Selenaaromatic rings in selenazolium and selenopyrylium salts are transformed to other rings in reactions other then cycloaddition. Examples are conversion of 1,2,4-selenadiazolium salt (67) to 1,3,5-selenadiazine (68) (Scheme 17), oxidative ring contraction of selenopyrylium salt (81) to selenophene (82), or replacement of selenium in the 2-selenachromylium salts (83) by two nitrogen atoms resulting in formation of benzodiazepines (84) (Scheme 21) [116],... 

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. 

The most general method for the formation of selenopyrylium salts from acyclic precursors involves the reaction of 1,5-diketones with a dibasic source of selenium, mainly hydrogen selenide, or by reaction of the 5-chloropenta-2,4-... 

Reactions of hydrazine and methylhydrazine with pyrylium or thiinium salts, e.g., 182, provide major routes to 4H-1,2-diazepines 183 and 1/7-1,2-diazepines 184 <1980CJC494>. Selenopyrylium salts react with anhydrous hydrazine in dry acetonitrile in a similar fashion (Scheme 90) <2005CPB60, CHEC-III(13.04.10)154>. 

CHa H H CeHs Selenopyrylium salt NaHS 65 116 31 (methanol/ ligroin)... 

S,6-Polymethylene derivatives of selenopyrylium salts are formed when the related 1,5-diketones are treated with zinc selenide in methanolic HCl (94CHE503). 

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