Electronic absorption spectra of alkyl- and phenyl-substituted pyrylium salts

Absorption spectra in the region 220–400 mμ have been determined for alkyl- and phenyl-substituted pyrylium salts. Three bands are apparent, in the decreasing order of wavelength, x, y, and x′ bands. These bands are differently influenced by substitution in and γ positions. Relationships of these bands with transitions in other aromatic compounds are established, and the effect of heteroatom variation in the series III–VI on the spectrum is discussed.     

Infrared spectra of thiopyrylium and pyrylium cations

Normal coordinate analysis has been carried out for the in-plane and out-of-plane vibrations of thiopyrylium (1) and pyrylium (2) cations which are isoelectronic with benzene, in order to investigate the structural characteristics (the contribution of the carbonium ion structures and the Kekulé structures to their resonance hybrid). Several sets of parameters for the double bond stretching constants have been chosen considering the delocalization of the positive charge. As a result, much more delocalization of the positive charge in 1 than in 2 has been found.     

Time-resolved interaction of polar solvents with excited pyrylium cations

The time-resolved fluorescence spectra of two pyrylium-ion derivatives have been investigated. In the temperature range 77 to 190 K, a red-shift of the fluorescence spectra of the order of 25–70 nm is observed and assigned to a fast solvent relaxation process. Time-resolved experiments carried out at 160 K showed a rapid decrease of the emission from the non-relaxed excited state at short wavelengths and a corresponding build-up of the emission of the relaxed one at longer wavelengths. At 120 K emission from the non-relaxed electronic state is predominant.     

Conversions of primary amino groups into other functionality mediated by pyrylium cations

Primary amines react with pyrylium cations to give pyridiniums which transfer the N-substituent to a wide range of halide, O-, S-, N-, C- and H-nucleophiles and undergo elimination and rearrangement reactions.Kinetic study of the formation and displacement steps has enabled the selection of substituents on the original pyrylium to optimise conditions for both steps. The procedure represents a widely applicable two-step sequence for the selective conversion of primary amino groups into many other functionalities under mild conditions in high yields.     

High resolution NMR spectroscopy of heteroaromatic cations. II—pyrylium,thiapyrylium and seleninium cations

The barriers to internal rotation about the C? N bond in several thiopiperidides have been determined by the NMR technique. It was found that the barrier height (ΔG^?) increases in the series cinnamoylthiopiperidide<thiobenzoylpiperidide<phenylthioacetylpiperidide. This trend was discussed in terms of the electronic structure, using HMO calculations. For m-and p-substituted cinnamoylthiopiperidides the barriers were shown to increase with the electron withdrawing character of the substituent in the aromatic ring.     

Steric and electronic structure of complexes of pyrylium and thiopyrylium cations with borabenzene anion

The coordination of pyrylium and thiopyrylium cations with borabenzene was studied by DFT [B3LYP/6-311++G(d,p)] calculations. The structures of charge-transfer molecular complexes formed by the aromatic ions were predicted. The stabilization is due both to electron density transfer and to covalent bonding.     

Palladium-catalyzed arylation of cyclopentadienes

Cyclopentadiene and metallocenes, typically zirconocene dichloride, are suitable substrates for multiple arylations with aryl bromides in palladium-catalyzed reactions. Thus, various aryl bromides bearing either an electron-donating or an electron-withdrawing substituent can react with these substrates to afford the corresponding 1,2,3,4,5-pentaaryl-1,3-cyclopentadienes in a single preparative step. Derivatives of cyclopentadiene, including di- and trisubstituted cyclopentadienes, and indene are arylated in a similar fashion.     

Reactions of heterocyclic cations with nitrogen-containing nucleophiles. 12. Reaction of pyrylium salts with azomethines

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.See [1] for Communication 11.Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 465–468, April, 1982.     

The structure of silyl cyclopentadienes

Calculations have been made in the MNDO approximation of the structures and energies of three isomeric forms of (η¹-C₅H₅)SiR₃ (R = H, Me) and of (η⁵-C₅H₅)SiR₃, together with potential energy curves for the folding of the C₅ ring in 5-R₃SiC₅H₅; all the η¹ species have planar C₅rings at equilibrium. In addition (1,2) and (1,3) shift mechanisms have been investigated for migration of both SiH₃ and hydrogen in (η¹-C₅H₅)SiH₃: the lowest energy pathway in each case is the (1,2) shift mechanism; structures and energies of the transition states are reported.     

Synthesis of β-carbonylphosphine oxides and phenyl-substituted ethylenediphosphine oxides. study of their complexing with alkali metals cations

The synthesis of some β-carbonylphosphine oxides and phenyl-substituted ethylenediphosphine oxides was carried out. Their complexing with alkali metals cations was studied. Compounds obtained were shown to possess clearly expressed Li/Na selectivity.     

Reactions of cyclopentadienes with phorone

Reactions of different cyclopentadienes with phorone were studied. Nonsubstituted and monosubstituted cyclopentadienes form annelation products,viz., 4,4,8,8-tetramethyl-1, 3a,4,5,6,7,8,8a-octahydroazulen-6-ones. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 721–724, April, 2000.     

On pyrylium cations,molecular graphs,topological indices for QSAR,and various other structural problems

In this autobiographical sketch, I will present my contributions in two areas of chemistry: experimental organic and theoretical chemistries.

     

Reactions of heterocyclic cations with N-containing nucleophiles. 17. Synthesis of pyrylium salts with three-ring azole substituents

2,6-Diphenylpyrylium perchlorate was hetarylated with imidazo- and pyrrolo-[1,2-a]benzimidazoles, and deeply colored 4-azolylpyrylium perchlorates were obtained.See [1] for communication 16.Communication 24 from the series Research on imidazo[1,2-a]benzimidazole derivatives. See [2] for communication 23.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 309–313, March, 1987.     

Conversion of methanol on a high-silica zeolite with divalent cations

The influence of divalent cations introduced into a high-silica zeolite by an ion exchange on its acidity and catalytic properties has been studied. The nature of the divalent cations has an influence on the distribution of the acid sites according to their strength, as well as on the activity and selectivity of action of the zeolite in the conversion of methanol. The primary conversion products of methanol, viz., dimethyl ether and ethylene, form on the acid sites of moderate strength. The hydrogen-redistribution reactions take place predominantly on the strong acid sites.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 1, pp. 114–118, January–February, 1986.     

Rearrangement of 3,5-dicyano-1,4-dihydropyridines to densely functionalized cyclopentadienes

3,5-Dicyano-1,4-dihydropyridines underwent ring contraction to give functionalized cyclopentadienes upon treatment with trifluoroacetic anhydride.     

Synthesis of highly alkylated functionalized cyclopentadienes

Tetra- and pentaalkylated cyclopentadienyl ketones and carboxylic acids are prepared by electrophilic allylation of enolizible 1,3-dicarbonyl compounds and successive acid catalyzed cyclisation.