R. S. Begunov

Effect of reducer’s nature on the reduction of N-(2-nitrophenyl)pyridinium chlorides

Pyrido[1,2-а]benzimidazoles and the other fused polycyclic imidazole derivatives containing a nodal nitrogen atom belong to the most interesting classes of organic compounds since they exhibit versatile biological activity: antitumor [1], immunomodulating [2], antiphlogistic [3], antibacterial, and fungicidal [4]. They are besides bioisosteric analogs of nitrogen bases and are capable of insertion into the DNA double helix [5]. Due to the high fl uorescence activity these heterocyclic compounds are employed in the paints production [6]. Therefore a great number of publications appears describing the new or modifi cations of the previously known procedures for the synthesis of similar heterocyclic systems [7]. The most promising and yet the least studied is the method based on the building up of the imidazole ring of the pyrido[1,2-а]-benzimidazole system through the reductive intramolecular cyclization of 1-(2-nitrophenyl) pyridinium salts. This methods is used seldom since there are insuffi cient data on the effect of various factors on the process of the reductive amination. The most essential factor is here the nature of electron donor [8, 9]. Depending on the structure of the latter a number of process may occur alternative to the intramolecular amination: the reduction of the pyridine fragment into piperidine moiety [8, 9], the formation of 1-(2-aminophenyl)derivative [9], the reaction of the pyridinium salt with the reagent (at the reduction with phenylhydrazine) [8]. The investigation of the effect of the reducer nature on the reaction direction was performed using reagents operating in the acid medium: TiCl3, FeCl2, SnCl2. The use of Na2S and the other agents for the reduction of the nitro compounds at рН > 7 is prevented by the hydrolysis of pyridinium salts occurring with the ring opening [10]. The reduction of 1-[2-nitro-4-(trifl uoromethyl)phenyl] pyridinium chloride (Iа) with titanium(III) chloride in the acidic water-alcohol solution led to an intractable mixture from which we isolated in a small yield (up to 23%) a compound that according to the 1H NMR and mass spectra corresponded to the product II resulting from the reduction of the nitro group. The 1H NMR spectrum of compound II contains the signals of pyridine protons: 9.15 d (2Н, Н2,6, J 8.5 Hz), 8.75 m (1Н, Н4), 8.35 m (2Н, Н3,5). The singlet of the amino group protons appears at 6.22 ppm due to the presence of an electron-acceptor

Synthesis and properties of poly[2-(4′-oxyphenylene)-5-benzimidazole] and a proton-exchange membrane produced on its basis

A monomer of the A-B type, 3,4-diamino-4′-carboxydiphenyloxide, has been synthesized via a series of consecutive transformations of 5-chloro-2-nitroaniline. The homopolycondensation of the monomer in Eaton’s reagent at 140°C yields poly[2-(4′-oxyphenylene)-5-benzimidazole] soluble in organic solvents. A membrane containing 51% H3PO4 (2.9 acid molecules pert monomer unit) and possessing a proton conductivity of 0.025 S/cm at 160°C is produced by doping a polymer film with 60% H3PO4.

Reaction of Reductive Intermolecular Heterocyclization of N-(2-Nitroaryl)pyridinium Chlorides with Salts of Variable Valence Metals

Depending on the nature of the electron donor the chemical reduction of N-(2-nitro-4-R-phenyl) pyridinium salts affords either primary amines like N(2-amino-4-R-phenyl)pyridinium chlorides or products of intermolecular cyclization, derivatives of pyrido [1,2-а]benzimidazole [1]. The yield and purity of the specific azaheterocycles depend on the nature of the reducing agent. The application of TiCl3 led to the formation of multicomponent mixture of compounds; from the mixture 1-(2-amino-4-R-phenyl)pyridinium chloride was isolated in a small yield. During the reduction with SnCl2 intramolecular amination took place. Yield of 7-R-pyrido[1,2-а]benzimidazole was 86–98%. The use of FeCl2 also allowed obtaining a fused tricycle system, but in significantly lower yield.

Benzophenone-Type Unsymmetrical Substituted Aromatic Diamines and Organosoluble Polyimides Therefrom

Benzophenone-type unsymmetrical substituted aromatic diamines of general formula were prepared starting with p-nitrobenzoyl chloride and substituted benzenes. Interaction of the diamines obtained with aromatic tetracarboxylic acids dianhydrides under the conditions of high-temperature solution polycyclocondensation in m-cresol led to the formation of new high molecular weight organosoluble polyimides.

Asymmetric benzophenone-series aromatic diamines and related soluble polyimides

Asymmetric aromatic diamines of the benzophenone series (3,4′-diamino-4-methylbenzophenone and 3,4′-diamino-4-methoxybenzophenone) were synthesized via the Friedel-Crafts reaction of 4-nitrobenzoyl chloride with an equimolar amount of toluene or anisole; the subsequent nitration of the products (4′-nitro-4-methylbenzophenone and 4′-nitro-4-methoxybenzophenone), yielding 3,4′-dinitro-4-methylbenzophenone and 3,4′-dinitro-4-methoxybenzophenone; and the reduction of the latter compounds. The high-temperature polycyclocondensation of the above diamines with aromatic tetracarboxylic dianhydrides in phenol solvents gave methyl-and methoxy-substituted aromatic polyimides soluble in phenol and amide solvents.

Effect of temperature and the nature of protonating agent on reduction of N-(2-nitroaryl)pyridinium chlorides

We selected 1-[2-nitro-4-(trifluormethyl)phenyl]pyridinium chloride 1а as a model substrate (Scheme 1). Trifluoromethyl group should favor the solubility of compounds in organic solvents of diverse nature [3, 4]. It was therefore expectable that at the extraction from the reaction mixture all reaction products would be isolated in a maximum quantity. In the study anhydrous 98% tin(II) chloride [7772-99-8] manufactured by Acros Organics was used in a ratio 1–SnCl2 1 : 3.05. The effect of temperature on the direction of the reduction process of compound 1а was studied in the range from 10 to 80°C (Table 1). The reaction was carried out in acidified water-alcohol mixture. The effect of the chosen factor was estimated by the overall and individual yield of forming products. The reaction products were isolated from the dry residue after evaporation of the liquid phase from the reaction mixture preliminary treated with NH4OH till рН 7–8. Compounds 2а and 3а were separated by boiling in hexane which did not dissolve compound 3а.

Poly(arylene oxides) containing sulfo acid groups: Synthesis, properties, and application

Key advances in the synthesis, characterization, and application of poly(arylene oxides) containing sulfo acid groups in main chains of macromolecules and side substituents are surveyed. The main advantages and drawbacks of various approaches to the synthesis of these polymers, such as postsulfonation of poly(arylene oxides), polycondensation with the use of sulfonated monomers, and transformations of polymers containing reactive groups, are analyzed.

Quantum chemical study of regioselectivity of reactions of substituted pyrido[1,2- a ]benzimidazoles with electrophiles

The geometric, charge, and electronic characteristics of 7-substituted pyrido[1,2-a]benzimidazoles and their cations were calculated using the DFT method with the B3LYP functional in the 6-31G** basis set. High regioselectivity of the reactions between the condensed imidazole derivatives and electrophilic agents was explained by the results of quantum chemical simulation. It was concluded that the SEAr reaction was orbitally controlled. According to Fukuís concept, the reaction center of the electrophilic attack was the C(8) atom of the heterocyclic system, which agreed well with the experimental data.

Electrochemical reduction of N-(2-nitro-4-R-phenyl)pyridinium salts using redox-mediators

Electrochemical reduction of N-(2-nitroaryl)pyridinium chlorides was accomplished in acidic aqueous alcoholic medium in the galvanostatic mode using tin, titanium, vanadium, and iron chlorides as redox-mediators. The use of SnCl2 as a mediator catalyst made it possible to shorten the electrosynthesis time as compared to the direct electroreduction on an electrode and prepare the intramolecular cyclization products, viz., substituted pyrido[1,2-a]benzimidazoles, in high yield. The influence of the mediator nature and its amount, current density, temperature, cathode material, medium acidity, and the substrate structure on the efficiency of reductive heterocyclization of N-(2-nitroaryl)pyridinium salts was studied.

Morpholine-substituted soluble polyimides

The interaction of undescribed 1,3-diamino-4-morpholinebenzene with dianhydrides of various aromatic tetracarboxylic acids yields morpholine-substituted soluble polyimides. The thermal properties of these polymers are studied.