Selenopyrylium

Selenopyran (8) was converted to selenopyrylium perchlorate 256 or chloride with trityl perchlorate or phosphorus pentachloride, respectively.90... 

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). 

Doddi, G., Ercolani, G., Thiopyrylium, Selenopyrylium, and Telluropyrylium Salts, 60, 65. 

As expected on the basis of the higher stability of sulfonium salts as compared with oxonium salts, thiopyrylium cations are more stable and less reactive than pyrylium cations hydride-accepting ability decreases in the order pyrylium> selenopyrylium> thiopyrylium [95], 2,4,6-Triphenyl-thiopyrylium salts react with ammonia and primary alkylamines forming the corresponding pyridine and pyridinium salts, respectively, but they do not react with aniline or its derivatives [96-99], As described below, the Se- or Te-analogs are less stable than the thiopyrylium salts. 

J Pyrylium Thiopyrylium Selenopyrylium Pyridine Pyridinium Pyridine- A-oxide... 

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-... 

Murphy PJ (2003) Selenopyrylium and benzoselenopyrylium salts In Houben-Weil science of synthesis. Thieme, Stuttgart, chap 14.10, p 817... 

Another series of thio- and selenopyrylium photosensitizers were prepared and evaluated for their ability to purge blood-borne pathogens <2007BMC4406>. The preparative route is illustrated for selenopyrylium iodide 193 (Scheme 23) (see Section 7.11.8.1). 

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>. 

Pseudobase formation by the pyrylium, thiopyrylium, and selenopyrylium cations is complicated by ring-opening reactions (Section V,A) which preclude a simple direct measurement of pKR + for these cations. In a kinetic study, Williams80 has found the ring opening of 2,4,6-trisubstituted pyrylium cations 23 to be controlled by pKa values in the range of 5.0-6.7 for R2,... 

Pyrylium (1) and its chalcogen analogs, thiopyrylium (2), selenopyrylium (3), and telluropyrylium (4), are the parent structures of an important class of six-membered heteroaromatic cations. 

UV Spectral Data of Pyrylium, Thiopyrylium, and Selenopyrylium, Perchlorates in Acetonitrile" ... 

---