Benzo pyrylium salts oxidation

At the same time, photolysis of 2,3-diaryl-2,3-epoxyindanones 14, as well as thermolysis (62JA1315), includes the reversible formation of red inner salts benzo[c]pyrylium-4-oxides 15 (63JA3529 64JA2084 84KGS167 86NKK1622). 

The unsubstituted benzo[c]pyrylium-4-oxide 19 was formed from iso-chroman-4-one derivatives 17 [76ACS(B)619] or from 18 (84CC702). All attempts to isolate oxide 19, for instance as a fluoroboric acid salt, failed because it reacted further by polymerization and dimerization [76ACS(B)619]. Even in substituted systems 15, in spite of added stabili-... 

AH attempts to convert dimer 263 into a dimeric 2-benzopyryIium salt, on treatment with triphenylmethyl or acetyl perchlorate, lead only to the rupture of the newly formed C—C bond and to the regeneration of the initial monomeric salt 261, unlike the behavior of dimers of monocyclic pyrylium cations [73DOK(212)370]. Dimerization may be considered a typical reaction for benzo[c]pyrylium-4-oxides of type 19, which react in dimerizations as 1,3-dipoles by analogy with their behavior in cycloadditions (Section III,E,2). 

Similar to aroxyl-benzo[b]pyrylium systems (78ZOR1643), there is no detectable delocalization of the unpaired electron on the benzo[c]pyrylium ring in 301-303 (87RRC417). The stability of the radical cation is determined in this case by the position of the aroxyl substituent in the cation, and the most stable is 301. The formation of diradical species 303 together with the monoradical cation, was indicated on oxidation of the corresponding 2-benzopyrylium salt. 

Under the action of Ph3P/pyridine in an atmosphere of oxygen, tellura-pyrylium and tellurachromylium salts undergo oxidative dimerization, affording l,l-dioxo(tellurapyranylidene)tellurapyrans 113 and 1,1 -dioxo(benzo[6]pyranilidene)tellurapyrans 114, the yields of each compound approaching 25% (87JOC2123). 

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See also in sourсe #XX -- [ , ]

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