2.4.6- Triarylpyrylium perchlorates

When 2,4,6-triarylpyrylium perchlorates and the 4,4 -dimethylbispyridinium dibromides 18 were heated in the presence of tiiethylamine/acetic acid in boiling ethanol, a double pyrylium ring transformation occurred to give high yields of the 4,4 -bis(2,4,6-triarylphenyl)bispyridinium salts 19 <96JHC(33)783>. 

Dihydroimidazo[2,l-b]oxazoles were prepared fi om an intramolecular nucleophilic ipso-substitution of 2-alkylsulfonylimidazoles <99S1613>. The synthesis of hitherto unknown 2-(2,4,6-triarylphenyl)substituted 4,5-dihydro-1/f-imidazolium perchlorates from 2-methyl imidazolium perchlorates and 2,4,6-triarylpyrylium perchlorate salts was published <99JC813>. Substituted aromatic heterocycles from reactions of 2,3-dihydrospiro[l/f-4-and... 

Water covalently interacts only with strongly electrophilic 2,4,6-triarylpyrylium perchlorates (possessing substituents like S03H and C02H) in the aryl group to equilibrate with the corresponding 2-hydroxy-... 

Acetate ions reversibly add to 2,4,6-triarylpyrylium perchlorates to form 2-acetoxy-2//-pyrans 125, as found for the case Ar = Ar = Ph in a dry Et3N-AcOH mixture (83JCS(P1)497] but with AcONa-H20 diketones 126 were the only products (84JPR287 85JPR529). 

Synthesis of 2-fiiryl acetonitrile derivatives has been achieved by thermally induced ring contraction on reaction of 2,4,6-triarylpyrylium perchlorates with sodium cyanide (Scheme 103).i48... 

Triarylpyrylium salts react with hydrazine to give 4//-l,2-diazepines 472-1°s,ioo vja g unstable intermediates 3.110 The reaction fails with pyrylium salts containing alkyl groups in positions 2 and 6, with the exception of 2,4,6-tri-tert-butylpyrylium perchlorate. In some cases it is advantageous to use a thiapyrylium salt in place of the pyrylium salt. Selected examples are given. 

Systems Containing Two Different Heteroatoms 6.1 Oxazepines.- 2-Substituted triaryl-1,2-oxazepinium perchlorates, the first examples of seven-membered heterocyclic cations with eight n-electrons, have been prepared by the reaction of 2,4,6-triarylpyrylium salts with nitrones, or N-arylhydroxylamines,... 

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