Synthesis and crystal structure of Schiff bases obtained by condensation of 2-aminopyridines with acrylic aldehydes

We synthesized a series of novel imines by reactions of 2-amino-4-methylpyridine with (hetero)aromatic derivatives of acrolein in the presence of molecular sieves (as a dehydrating and acid-catalyzing agent). We determined the molecular and crystal structure of two 2-pyridylazomethines containing the CH=CH–CH=N group by X-ray diffraction analysis.Latvian Institute of Organic Synthesis, Riga LV-1006. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 778–785, June, 2000.     

Structure and substitution effects on the thermotropicity of some polyesters and model compounds

Abstract

The variations which occur in the thermal stability of the nematic mesophase as a function of the structure of the mesogenic moiety are considered here for the role played by three types of modifications. These are changes in the chemical nature of the mesogenic group, variation of the axial ratio of the rigid core and the presence of lateral substituents on the aromatic rings. Low molecular weight and polymeric liquid crystals of similar chemical nature have been investigated in order to see if parallel structure—property relationships exist between the two groups of compounds. In particular, starting from a mesogenic group built up of three aromatic rings connected by ester bonds, we have introduced the following modifications: (i) substitution of the central —COOC₆H₄OOC—with the—CH[dbnd]N—N[dbnd]CH— group; (ii) addition of two oxybenzoic end units to increase the length of the mesogenic moiety; (iii) introduction of two or more lateral methoxy substituents on the aromatic rings. The compounds were obtained by low temperature solution esterification between acyl chlorides and phenolic derivatives in the presence of a tertiary amine. Syntheses generally took place through the preliminary preparation of suitable intermediates. The thermal stability and the nature of the mesophases have been examined by different techniques. An interpretation of the results on the basis of the axial ratio and the strength of orientation dependent mutual attractions is attempted for model compounds. As far as polymers are concerned thermodynamic parameters follow the expected trend, if compared with those of low molecular weight analogues. Qualitatively models and polymers exhibit a similar dependence of mesophase stability on geometrical and electronic effects.     

Hypervalent Iodine Oxidation of Amines in the Presence of Nitroso Compounds: A Method for the Preparation of Unsymmetrically Substituted Azoxy Compounds

Various amines and amino derivatives such as (tert-butylamine, 4-amino-1,2,4-triazole-p-toluenesulfonamide), and cyanamide, when treated with |(diacetoxy)iodo|benzene in the presence of nitroso compounds (2) yield unsymmetrically substituted azoxy compounds (3).     

Spectral-luminescent properties of oxazole derivatives with annelated aromatic and heterocyclic rings in neutral and acid media

An investigation was carried out of the spectral-luminescent and acid-base properties at the stage of formation of the hydrogen bond and during the protonation of compounds with annelated aromatic and heterocyclic rings, obtained by introduction of bridging groups -CH=CH- (I), -CH=N- (II) and -CO-N(CH₃)-(III) in the 4- and 2-positions of the molecules of 4-substituted derivatives of 2,5-diphenyloxazole. The nature of the reaction center was estabished, and an analysis was carried out of its sensitivity to the electronic influence of the substituents, and the reasons for the observed differences in the properties of compounds of various reaction series are discussed. A comparative analysis of the fluorescent properties of the neutral and protonated forms of the oxazole derivatives studied was made and the conclusion that the generation is possible of laser emission by the protonated forms of compounds of the reaction series (I) was confirmed.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, No. 4, pp. 343–349, July–August, 1992.     

Use of Tetramethylthiuram Disulfide in Synthesis of Nitrogen-containing Heterocyclic Compounds

We have developed a method for synthesis of aryl isothiocyanates by means of thiocarbamoylation of aromatic amines by tetramethylthiuram disulfide followed by degradation of the intermediate N₍₁₎-aryl-N,N-dimethylthiourea by concentrated HCl. We have shown that thiocarbamoylation of 4-amino-5-ethyl-4H-1,2,4-triazole-3-thiol occurs at the 2 position of the triazole ring, while thiocarbamoylation of 4-amino-3-methyl-6-phenyl-4,5-dihydro-1,2,4-triazin-5-one leads to the dihetaryl-substituted thiourea. We consider the possibility of using N₍₁₎-aryl-N,N-dimethylthioureas as analogs of isothiocyanates in reactions with N-nucleophiles.__________Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 775–780, May, 2005.     

Theoretical studies on the molecular electron densities and electrostatic potentials in azacubanes

Energetics and the charge distributions in azacubanes (C₈NH_8–) have been obtained using the ab initio Hartree–Fock, second-order Mø øller–Plesset perturbation theory and hybrid density functional methods. For diazacubane to hexaazacubane the lowest-energy conformers have nitrogen atoms occupying the face opposite corners of a cube. The topography of the molecular electrostatic potential and the electron density of azacubane conformers have been investigated. The electrostatic potential studies have shown that successive substitution of nitrogen instead of CH groups of cubane engenders smaller and more localized electron-rich regions around the nitrogens of a cube. Further the bond ellipticity and the electron density at the bond critical point of the X–N bonds (X=C or N) in a cubanoid increase from azacubane to octaazacubane. The heats of formation of azacubanes calculated by the isodesmic reaction approach using different levels of theory correlate well with the electron density at the bond critical point of X–N (X=C or N) bonds in a cubanoid.     

Catalytic activity of amines in the oxidation of anthrone

The rate of non-radical oxidation of anthrone with molecular oxygen, catalyzed by aliphatic amines with different substituents, amino acids, aromatic amines, and compounds possessing several basic centers, was measured. The catalytic activity of amines decreases in the series RO(CH₂) _n NH₂ > RNH₂ > morpholine derivatives > RR′N(CH₂) _n NH₂ > guanidine > RR′NH > RR′R″N > 1,4-diazabicyclo[2.2.2]octane > amino acids > (R)PhNH₂. A relation was found between proton affinities and structural parameters of the amines and their catalytic activity in the title reaction.     

Alkenylation of arylamines and <Emphasis Type="Italic">N</Emphasis>-arylacetamides with acetylene compounds in superacids

Vinyl type cations generated in superacid HSO₃F by the protonation of the triple bond of acetylene compounds efficiently react with arylammonium ions and N-arylacetamides yielding alkenylation products of the aromatic rings in the given amino derivatives. The regio-and stereoselectivity of electrophilic aromatic substitution was investigated involving vinyl type cations and arylammonium ions or N-arylacetamides in HSO₃F.     

l,3-Dipolar cycloaddition of unsatu rated ferrocene derivatives with carbonitrileN-oxides

3,5-Disubstituted isoxazolines and isoxazoles have been synthesized using 1,3-dipolar cycloaddition of ferrocene derivatives FcCH=CH₂, FcCOCH=CH₂ and FcCCH with aliphatic and aromatic carbonitrileTV-oxides.Translated fromIzyestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 139–142, January, 1994.     

Selective N-oxidation of aromatic amines to nitroso derivatives using a molybdenum acetylide oxo-peroxo complex as catalyst

The molybdenum acetylide oxo-peroxo complex obtained in situ by the treatment of the corresponding molybdenum acetylide carbonyl complex, CpMo(CO)₃(CCPh); Cp = η⁵-C₅H₅ with H₂O₂, has been used as an efficient catalyst for selective N-oxidation of primary amines to nitroso derivatives. Excellent amine conversion (up to 100%) and very high selectivity for nitroso compounds (99%) have been obtained using 30% hydrogen peroxide as an oxidant. The oxo peroxo Mo(VI) complex has also been found to be very active for the oxidation of various substituted primary aromatic amines with electron donating as well as electron withdrawing substituents on the aromatic ring.     

Exploring the impacts of the vinylogous anomeric effect on the synchronous early and late transition states of the hydrogen molecule elimination reactions of cis-3,6-dihalocyclohexa-1,4-dienes

LC-ωPBE, B3LYP, and M06-2X methods with the 6–311+G** basis set on all atoms and natural bond orbital (NBO) interpretation were performed to investigate the roles and contributions of the effective factors on the potential energy surfaces of the hydrogen molecule elimination reactions of cyclohexa-1,4-diene (1) and its cis-3,6-dihalo derivatives [halogen=F (2), Cl (3), Br (4)] to hydrogen molecule and their corresponding aromatic rings. The ring puckering in compound 2 (which results from the repulsive electrostatic interactions between the natural bond orbital dipole moments of two C-F bonds) shortens the allylic hydrogen atoms’ distance, leading to the smaller barrier height in compound 2 compared to that in compound 1. The barrier heights of the hydrogen molecule elimination reactions increase from compounds 2 to 4 while their corresponding exothermic characters decrease. The variations of the advancements of transition state structures (δB _av) reveal that the hydrogen molecule elimination reactions of compounds 2–4 do not obey the Hammond-Leffler postulate. In compound 2, the ring puckering shortens the allylic hydrogen distance (d _H8-H10) while d _H8-H10 values increase going from compounds 2 to 4, leading to the increase of their corresponding hydrogen molecule elimination reactions barrier heights. Interestingly, the variations of the vinylogous hyperconjugative anomeric effects justify the directions of the rings puckering going from compounds 2 to 4. The increase of the activation exchange components [PETR _(TS)-PETR _(GS)] going from compounds 2 to 4 correlates well with their corresponding hydrogen molecule elimination process barrier heights.     

Microwave-assisted synthesis of pyrazolo[3,4-d]pyrimidines from 2-amino-4,6-dichloropyrimidine-5-carbaldehyde under solvent-free conditions

The microwave-induced synthesis of pyrazolo[3,4-d]pyrimidines 4 in the reaction of N⁴-substituted-2,4-diamino-6-chloro-5-carbaldehydes 3 with hydrazine is described here. Precursors 3 have been prepared by the mono-amination of 2-amino-4,6-dichloropyrimidine-5-carbaldehyde 2 with aliphatic and aromatic amines. The reaction times with primary amines were relatively shorter than for secondary amines.     

Mass-spectrometric and quantum-chemical study of fragmentation of diallyl esters of dicarboxylic acids

In a mechanistic study of thermal breakdown of diallyl polymers, six diallyl esters of dicarboxylic acids have been investigated by means of mass spectrometry. A characteristic feature of the fragmentation of these compounds is the low stability of the molecular ions and detachment of the allyl cation, the peak of which is usually the highest in the mass spectrum. In interpreting such an unusual path of fragmentation of esters, quantum-chemical calculations have been carried out in the MINDO/3 approximation; the preferred conformation of the diallyl maleate molecule and the distribution of electron density in this conformation have been determined, and the most stable cyclic structure of the intermediate cation [CH=CH(CO)₂OH]⁺ has been established. The nature of the bridge between the carboxyl groups in diallyl esters of dicarboxylic acids has practically no influence on the direction of fragmentation. The decisive factor in the fragmentation is the electrostatic interaction of charges on the atoms of carbonyl carbon and ester oxygen of the second carboxyl group. A fragmentation scheme with the formation of intermediate cyclic cations is proposed.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 3, pp. 300–307, May–June, 1990.     

Study of intermolecular interactions and complex formation of aminofurazans by IR spectroscopy

The IR spectra of 3-amino-4-nitrofurazan (1) and 4-amino-4-nitroazoxyfurazan (2) in the crystalline state and in solutions in CH{in2}Cl{in2}, CCl{in4}, and MeCN have been studied. It was shown that both compounds exist in the solid state as self-associates, which are destroyed on dissolution in an organic solvent. Compouns1 and2 form associate complexes with MeCN, the energies of formation of which are –5 and –3 kcal mol{su–1}, respectively.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2242–2246, December, 1994.     

Synthesis of pyridinium salts by the reaction of α, β-unsaturated ketones,primary amines,and compounds with labile hydrogen atoms

The reaction of , -unsaturated ketones or Mannich bases of ketones with primary aromatic amines and ketones (monoketones or dimedone) in the presence of polyhalo-alkanes leads to pyridinium, 5,6,7,8-tetrahydroquinolinium, or sym-octahydroacridinium salts. The reaction of benxalcyclohexanone with primary aromatic amines and malonodinitrile makes it possible to obtain 2-amino-3-cyano-5,6,7,8-tetrahydroquinolinium salts.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1060–1064, August, 1985.     

Nontraditional Interpretation of Deviations from the Brönsted Relationship: Effect of Structural and Solvation Factors on the Equilibrium and Kinetic Characteristics of the CH Acidity in Polar Basic Nonaqueous Media

A concept is suggested for explaining deviations of certain CH acids from the linear Brønsted relationship. The major attention is given to ion-dipole interaction between the molecules of a polar aprotic solvent and dissolved carbanions. The concept is based on correcting the experimental pK _a values by eliminating the contributions from electrostatic solvation using data on the ionization constants of CH acids in the gas phase (H ^g). By the examples of acid dissociation of methyl CH bonds under conditions of established equilibrium in DMSO and kinetic data for deuterium exchange in a solution of an alkali metal amide in liquid ammonia, it was shown that for a series of compounds PhM(CH₃) _n-1 and M(CH₃)_n (M = N, O, P, S, CO), and also for some other methyl derivatives all kinds of deviations from the Brønsted relationship are realized (those originating from specific conditions of stabilization of the transition state in the course of reaction; those due to electrostatic solvation of the equilibrium carbanions; and the deviations resulting from combined effect of the kinetic and equilibrium factors). Also, the Brønsted relationships were obtained for ionization of CH acid series covering compounds with aliphatic, quasiaromatic, and aromatic CH bonds (the deuterium exchange was performed in liquid ammonia without a catalyst). The Brønsted coefficient 0.65 in this relationship suggests a higher degree of deprotonation of the CH bond in the transition state as compared to the catalytic exchange ( 0.3). The revealed difference is due to the different effect of electronic factors: In the catalytic deuterium exchange, the major contribution to the activation free energy (log k _D) is made by the resonance effects of substituents, whereas in the noncatalytic deuterium exchange the inductive effect prevails.     

Amination of 5-azacinnoline with aromatic amines

The 5-azacinnoline molecule was subjected to quantum-mechanical calculation by the Hückel method. The formation of 4-amino derivatives in the case of the reaction of 5-azacinnoline with aliphatic amines in the presence of an oxidizing agent and of 4,4-bis(5-azacinnolinyl) in the case of dimerization in an oxygenfree medium was substantiated theoretically. The possibility of reactions with anions of aromatic amines was predicted by means of the Klopman method. It is shown that, in practice, the reaction is actually accelerated and that, in conformity with theory, the reaction center is the nitrogen atom of the aromatic amine. Possible products involving reaction with the participation of the pcarbon atom of the arylamine were not recorded. As in the case of aliphatic amines, the formation of a dimer was observed in an oxygen-free medium. The structures of the compounds obtained were proved by means of a combination of physicochemical methods.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 809–812, June, 1978.     

Synthesis of 5-arylidene derivatives of thiazane-2, 4-dithione

Thiazane-2,4-diones and their 3-aryl derivatives readily condense with aromatic aldehydes to give 5-arylidene derivatives. The compounds obtained are characterized by absorption maxima in the 290–310 m band, as well as by ill-defined bands at 260–270 and 420–440 m. The IR spectrum of 5-benzylidenethiazane-2, 4-dithione has bands at 7.02 (N-C-S), 7.52 (CH₂), 14.62 and 15.01 (C-S-C).     

A variety of oxidation products of antioxidants based on N,N′-substituted p-phenylenediamines

Electrochemical and spectroscopic (EPR, UV–Vis, IR) studies of the aromatic secondary amines N,N′-diphenyl-1,4-phenylenediamine (DPPD), N-phenyl-N′-isopropyl-p-phenylene diamine (IPPD), N-phenyl-N′-(α-methylbenzyl)-p-phenylenediamine (SPPD) and N-phenyl-N′-(1,3-dimethyl-butyl)-p-phenylenediamine (6PPD), which represent the most important group of antioxidants used in the rubber industry, are presented. During oxidation, all the compounds show reversible redox couples in acetonitrile/0.1 M TBABF₄. The first oxidation potential depends substantially on the R substituent at the –N′H– moiety. Very similar UV–VIS spectra of monocation radicals and dications for all the compounds were observed by applying anodic oxidation as well as oxidation by tert-butyl hydroperoxide both in air and in inert atmosphere. The samples with N′-bonded aliphatic carbon in the molecule (e.g. IPPD) heated in air undergo consecutive chemical reactions leading to the formation of –N′C– group. By the use of RO₂ radicals only very low concentration of nitroxide radicals was obtained. Very high concentration of nitroxide radicals was achieved using 3-chloroperbenzoic acid. In the oxidation of investigated aromatic secondary amines with powder PbO₂ no EPR spectra were observed and UV–Vis and IR studies indicate the rapid formation of the final dehydrogenated oxidation product.     

Reaction of 2,3-dioxo-4-(N,N-dimethylaminomethylene)hexahydroazepine with hydroxylamine

Depending on the conditions selected, the reaction of 2,3-dioxo-4-(N,N-dimethylaminomethylene)hexahydroazepine with hydroxylamine gives 2,3-dioxo-4-formylhexahydroazepine 4-oxime, 8-oxo-8H-4,5,6,7-tetrahydroisoxazolo[5,4-c]azepine, or 2-oxo-3-hydroxy-4-cyano-2H-1,5,6,7-tetrahydroazepine. The reaction of the latter with aromatic amines and hydrazine hydrate was used to synthesize 3-arylamino-2-oxo-4-cyano-2H-1,5,6,7-tetrahydroazepines and 3-amino-8-oxo-8H-4,5,6,7-tetra-hydropyrazolo[5,4-c]azepine, respectively. The structures of the compounds obtained were confirmed by the IR, UV, and PMR spectra.Communication XXXI from the series Research on Lactams. See [1] for communication XXX.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1252–1255, September, 1978.