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The photobiscyclization reaction of N-azomethine pyridinium derivatives was investigated and the final and intermediate photoproducts were isolated. The first step of the reaction involves dihydro intermediate self-trapping by a 1,5-sigmatropic proton shift.

2,4,6-Substituted pyrylium salts add azomethines to give pyridinium salts and aromatic aldehydes. The latter can be condensed with the methyl groups of the pyridinium salts. Benzaldoxime, benzalazine, benzalphenylhydrazine, urea, thiourea, and phenyl isothiocyanate react with 2,4,6-triphenylpyrylium perchlorate similarly to give, respectively, 2,4,6-triphenylpyridine N-oxide, 2,4,6-triphenylpyridine, or N-substituted 2,4,6-triphenylpyridinium perchlorates.

On the basis of the measured basicity constants of pyrylium and pyridinium salts containing p-aminophenyl substituents it is shown that the positive charge in the pyrylium cation is considerably higher than in the pyridinium cation. The σ constants of the pyrylium and pyridinium substituents, which show that the magnitude of the electronic effect of the pyrylium ring is considerably higher than that of the pyrydinium ring, were calculated. The reaction of the indicated pyrylium salts with some electrophilic and nucleophilic reagents was examined.

2,4,6-Triphenylpyrylium perchlorate is converted to 2,4,6-triphenylpyridine in reactions with urea and N-acetyl- and N,N-dimethylureas, whereas it is converted to 1,2,4,6-tetraphenylpyridinium perchlorate on reaction with N,N′-diphenylurea. The reaction of pyrylium perchlorates with thiosemicarbazide and semicarbazide leads to 1-thiocarbamido- and 1-carbamidopyridinium salts. The latter reacts with 2,4,6-triphenylpyrylium perchlorate to give 1-aminopyridinium salts, which were acylated with acetic anhydride. Difficult-to-obtain 2-alkylthio-4,6-diarylpyrimidines were synthesized in 40–93% yields by the reaction of 2,4,6-triarylpyrylium salts with S-alkylisothioureas.

2,6-Diphenylpyrylium perchlorate was hetarylated with imidazo- and pyrrolo-[1,2-a]benzimidazoles, and deeply colored 4-azolylpyrylium perchlorates were obtained.

The recyclization reactions of 2,4,6-triphenylpyrylium perchlorate with hydrazine and methyl-, phenyl-, benzoyl-, and benzalhydrazines in dimethylformamide (DMF), which proceed differently than in ethanol, were examined. 7-Oxo and 7-thioxo derivatives of 2,3a,5-triphenyl-3H-pyrazolo[1,5-c]pyrimidine were obtained by transformation of 2,4,6-triarylpyrylium salts with semicarbazide and thiosemicarbazide in DMF. The tautomeric forms of the products were established by mass spectrometry and chemical transformations.

The pyridinium ring as a substituent in aniline is an electron acceptor, the effect of which is comparable to the effect of NO2 and N(CH3)2 groups. Correlation of the reactivities with the basicities of the amino groups is not observed in the investigated reactions of N-(aminophenyl)pyridinium perchlorates with some electrophilic reagents, inasmuch as steric factors apparently play a greater role.

The recyclization of 2,6-diphenylpyrylium perchlorate under the influence of isothioureas, guanidine, 2-aminobenzimidazoles, 2-aminonaphth[1,2-d]imidazole, 2-aminothiazole, 2-aminobenzothiazole, and 2-aminopyridine was studied. The examined reactions lead to monocyclic or condensed pyrimidines.

The reaction of 2,6-diphenylpyrylium perchlorate with semi- and thiosemicarbazides in ethanol leads to 1-carbamoyl- and 1-thiocarbamoyl-3-phenyl-5-phenacyl-4,5-dihydropyrazoles, the cyclization of which yields 2,5-diphenyl-7-oxo(thio)-pyrazolo[1,5-c]pyrimidines. The tautomeric form of the latter is established by comparing their electronic absorption spectra with the spectra of the methyl derivatives.

The direct interaction of 2,6-diphenylpyrylium perchlorate with pyrazoles and pyrazolones led to the synthesis of 4-azolylpyrylium salts, which readily cleave a molecule of perchloric acid in the case of the N-unsubstituted pyrazolones, being converted to pyranylidene derivatives.

New data on reactions of pyrylium salts with nitrogen-containing nucleophiles, occurring both with retention of the pyrylium ring and with recyclisation, are considered. The extensive possibilities for the employment of pyrylium salts in the synthesis of many functional compounds of the aliphatic and aromatic series and of different nitrogen- and oxygen-containing three-, five-, six-, and seven-membered heterocycles, including condensed heterocycles, are demonstrated. The bibliography includes 184 references.

1,3-Diphenylpyrimido[1,2-a]benzimidazolium perchlorates were obtained by reaction of 2,4,6-triphenylpyrylium perchlorate with 2-aminobenzimidazoles.

2,4,6-Triphenylpyrylium perchlorate reacts with most heterocyclic amines in dimethylformamide to give quaternary pyridinium salts. 2,4,6-Trimethylpyrylium perchlorate forms similar products only up to a certain limit of the basicity of the amine, below which a proton is transferred from theγ-methyl group of the pyrylium salt to the pyridine nitrogen atom of the heteroring to give the perchlorate of the starting heterocycle. The residual 2,6-dimethyl-γ-methylenepyran is polymerized to a hexamer.

2,4,6-Triphenylpyrylium perchlorate reacts with methylguanidine to give 1-methyl-2-amino-4,6-diphenylpyrimidinium perchlorate, which undergoes the Dimroth rearrangement to give 2-methylamino-4,6-diphenylpyrimidine. 2,4,6-Triarylpyrylium perchlorates react with guanidine to give N-pyrimidinylpyridinium salts. Pyrylium salts react with aminoguanidine, sulfanilylguanidine, and symmetrical diphenylguanidine at one amino group to give the corresponding pyridinium salts.

The reaction of pyrylium salts with azomethines leads to the formation of styrylpyrylium, styrylpyridinium, and 4-arylbenzylaminopyrylium salts. The reaction of the latter with ammonia and amines gave pyridines and pyridinium salts with a tertiary amino group as a substituent.

The reaction of 2,6-diphenylpyrylium perchlorate with methylamine and various anilines in acetic acid leads to pyridinium salts; 3,4-bispyridinium perchlorates were obtained in dimethylformamide. The reaction of 2,6-diphenylpyrylium perchlorate with hydrazine and the sodium salt of hydroxylamine leads to 3-phenyl-5-phenacyl-2-pyrazoline and -2-isoxazoline.

A number of N-aminoethyl-, N-hydroxyethyl-, and N-mercapto-ethylbenzimidazoles have been synthesized, and their behavior toward sodamide investigated. The influence of the basicity of the benzimidazoles on the course of the Chichibabin reaction is discussed.

The acid properties of primary C-amino-groups in amines, amides, and amidines have been examined. The methods of preparation and the physical and chemical properties of the metal salts of amines are discussed. The bibliography includes 227 references.

The reaction of pyrylium salts with primary amines of the benzimidazole series gives benzimidazolylpyridiniumperchlorates. The bacteriostatic action of the synthesized preparations was investigated.

2,4,6-Substituted pyrimidines were obtained by reaction of 2,4,6-triarylpyrylium perchlorates with amines. 2,4-Substituted pyrimidines were similarly synthesized from 2,6-diphenylpyrylium perchlorate.

2,4,6-Trimethylpyrylium perchlorate reacts with heterocyclic compounds containing apyridine nitrogen atom and having basicities higher than 9 pKa units (in acetonitrile) through a step involving the formation of a methylenepyran. 4-Methyl-2,6-diphenyl- and 2-methyl-4,6-diphenylpyrylium perchlorates react with benzimidazole to give 1,2-ethanediylidenebispyrans. Methyl-substituted pyrylium salts react with 2,6-diphenylpyrylium and flavylium perchlorates in the presence of benzimidazole to give methylidynecyanines and with acetic anhydride to give trimethylidynecyanines.

The pyrylium salt (I) reacts with the semicarbazides (II) to give the pyrazolines (III) which are transformed into the acetyl derivatives (IV) and the dinitrophenylhydrazones (V).

2-Substituted 3,5,7-triaryl-1,2-oxazepinium perchlorates were obtained by the reaction of 2,4,6-triarylpyrylium salts in dimethylformamide with nitrones and N-arylhydroxylamines. The products are the first representatives of seven-membered cations with eight π electrons.

The reaction of 2,6-diphenylpyrylium perchlorate with methylamine and various anilines in acetic acid leads to pyridinium salts; 3,4-bispyridinium perchlorates were obtained in dimethylformamide. The reaction of 2,6-diphenylpyrylium perchlorate with hydrazine and the sodium salt of hydroxylamine leads to 3-phenyl-5-phenacyl-2-pyrazoline and -2-isoxazoline.

The reaction of pyrylium salts with azomethines leads to the formation of styrylpyrylium, styrylpyridinium, and 4-arylbenzylaminopyrylium salts. The reaction of the latter with ammonia and amines gave pyridines and pyridinium salts with a tertiary amino group as a substituent.

2,4,6-Substituted pyrimidines were obtained by reaction of 2,4,6-triarylpyrylium perchlorates with amines. 2,4-Substituted pyrimidines were similarly synthesized from 2,6-diphenylpyrylium perchlorate.