Reactions of aromatic and heteroaromatic compounds bearing electron-acceptor substituents

Dimethyl(2-thienyl)sulfonium salts were synthesized for the first time. The corresponding triiodomercurates were obtained by the reaction of methyl 2-thienyl sulfide or its substituted derivatives with methyl iodide and mercuric iodide. Sulfonium perchlorates are formed as a result of the reaction of thiophene compounds with dimethyl sulfoxide in the presence of POCl₃ and perchloric acid. The HgI₃ ^– anion was replaced by NO₃ ^– by means of an anion-exchange resin. The methods for the dimethylation of sulfonium salts with conversion of them to the corresponding sulfides were studied; the conditions for obtaining quantitative yields from these reactions by means of an anion exchange resin in the acetate form were found.See [1] for communication VII.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 165–168, February, 1972.     

Reactions of aromatic and heteroaromatic compounds bearing electron-acceptor substituents

Complexing with aluminum chloride can change the specificity of the bromination of furfural in such a way that the major product becomes 4-bromofurfural. Consequently, as in the thiophene series, reinforcement of the electron-acceptor capacity of the carbonyl group by means of the complexing deactivates the free 5 position so much that the 4 position of the furan ring becomes the most active.See [1] for communication X.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 597–600, May, 1972.     

Reactions of aromatic and heteroaromatic compounds having electron-acceptor substituents

The chloromethylation of 2-acetothienone and 2-formylthiophene with , -bischloromethyl ether in 60–100% sulfuric acid was studied. An increase in the acidity of the medium promotes the formation of 4-substituted products, which, as in nitration and bromination, is explained by protonation of the carbonyl group, leading to intensification of its electron-acceptor capacity.See [1] for communication VI.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1353–1357, October, 1971.     

Reactions of aromatic and heteroaromatic compounds having electron-acceptor substituents

The composition of the products formed in the bromination of complexes of furfural with AlCl₃ and methyl furan-2-carboxylate with AlBr₃ in chloroform and dichloroethane was studied by PMR spectroscopy and gas-liquid chromatography. Some literature data pertaining to these reactions are refined and corrected. The pathways for the formation of chloro derivatives under the examined conditions are discussed.     

Reactions of aromatic and heteroaromatic compounds containing electron-acceptor substituents

A method was developed for the preparation of 4-chloromethyl-2-acylthiophenes and m-(chloromethyl)acylbenzenes in up to 65% yields by the action of paraformaldehyde and anhydrous aluminum chloride on the corresponding carbonyl compounds. The reaction mechanism is discussed.See [1] for communication XXII.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1474–1476, November, 1978.     

Reactions of aromatic and heteroaromatic compounds containing electron-acceptor substituents

Synthetic methods based on accessible furan compounds of 5-benzyl(3-furyl)carbinol, a necessary component for the preparation of modified pyrethrins, were studied. The carbinol was obtained in 24% overall yield by a five-step synthesis starting from 4-bromofuran-2-carboxylic acid, for the preparation of which an improved method is proposed. Acylation of benzene with the chloride of the latter acid gave 4-bromo-2-benzoylfuran (in 77% yield), the reduction of which by the action of AlCl₃ + LiAlH₄ gave 4-bromo-2-benzylfuran (in 74% yield). The latter was treated with butyllithium and dimethylformamide to give 5-benzyl-3-formylfuran, which was converted to the carbinol in quantitative yield by the action of LiAlH₄.See [1] for communication XXI.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 306–310, March, 1978.     

Reactions of aromatic and heteroaromatic compounds carrying electron-acceptor substituents. 26. Acylaminomethylation of 2-acylthiophenes, 2-thiophenecarboxylic acid,and its esters

The reaction of 2-thiophene aldehyde, 2-acetylthiophene, 2-thiophene carboxylic acid, and its methyl ester with N-(hydroxymethyl)chloroacetamide in concentrated sulfuric acid yields a mixture of 4- and 5-(N-chloroacetylamino) methyl derivatives, the former being preferred.For Communication 25, see [1].Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 793–797, June, 1986.     

Reactivities and structures of compounds of the thiophene and furan series bearing electron-acceptor substituents

The experimental data on orientation in electrophilic substitution reactions of compounds of the furan and thiophene series that bear electron-acceptor substituents were examined. Within the framework of the CNDO/2 method, the electronic structures, dipole moments, and spin-spin coupling constants in the PMR spectra were calculated for model systems — 2-formylthiophene, furfural, and their oxygen-protonated forms. The results of the calculations are compared with the available experimental data on the dipole moments and spin-spin coupling constants, which made it possible to discuss the geometrical structures of the compounds. An analysis of data on the chemical behavior of these compounds demonstrated that, in contrast to the charges found using the -electron approximation, the total charges on the atoms calculated by the CNDO/2 method are rather effective indexes of the reactivity.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 155–164, February, 1972.     

Some new approaches to modifying aromatic and heteroaromatic compounds by means of fluorine-containing substituents

Modification of physiologically active substances by means of fluorine atoms or fluoroalkyl groups is known in numerous cases to lead to compounds with a markedly higher activity. The optimum change in the properties is considered to be achieved by inserting 1-3 fluorine atoms into the molecule. Therefore modifications of compounds by such groups as CHF₂, CF₃, CH₂F are most frequently used in synthesis of fluorine-containing pharmaceutical and agricultural chemicals.

At the same time, the data obtained in recent years indicate the existence of some others regularities. Thus, in a number of cases highly active drugs have been revealed among highly fluorinated substances containing polar groups of atoms in the molecule. The physiological activity of fluorine-containing compounds seems to be determined not so much by the degree of fluorination as by the relationship between the hydrophobic and the hydrophilic properties. This conclusion is quite justified, since it is the compound's lipophilic-hydrophilic balance that determines its transport in biosystems and the possibility of the interaction with the lipoprotein sites of biomembranes. Moreover, compounds with a heightened fluorine con-     

Reaction of aromatic and heteroaromatic compounds bearing electron-accepting substituents 25. Synthesis of (5-benzyl-3-thienyl)methanol from 2-benzoylthiophene

Under the action of paraformaldehyde and AlCl₃, 2-benzoylthiophene has been converted into 2-benzoyl-4-chloromethylthiophene, which on treatment with anhydrous sodium acetate has given 4-acetoxymethyl-2-benzoylthiophene. The reduction and simultaneous saponification of the latter under the conditions of the Kizhner reaction has yielded (5-benzyl-3-thienyl)methanol.For Communication 24, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 472–474, April, 1980.     

A novel amination of aromatic and heteroaromatic compounds

Vinyl azides act as NH⁺₂ equivalents in reaction with aromatic or heteroaromatic lithium derivatives thus providing a direct method for amination of such compounds.     

Luminescence-laser classification of heteroaromatic and aromatic compounds.

The luminescent and laser properties of heteroaromatic and aromatic compounds are reviewed and discussed on the basis of all possible mutual arrangements of singlet and triplet states. All heteroaromatic compounds are divided into five classes. It is shown that a heteroaromatic compound can only be an effective laser dye if it belongs to class V (a situation where the Tnpi* level lies at higher energy than the S1(pipi*) level). Moreover, it is shown that the energy interval between the Tnpi* and S1(pipi*) states must be no less than 1000 cm - since the rate constant of the non-radiative process S1(pipi*)[symbol in text]Tnpi*[symbol in text]T1(pipi*) is usually 100 times greater than the fluorescence rate constant. The classification is extended to compounds with orbitals of pi/,pi*, pi,nupi* and pi/,nupi* nature. Pure aromatic compounds, the spectral-luminescent properties of which are solely determined by transitions of pi-electrons (pi --> pi*), are also divided into five classes, depending on the mutual arrangement of the Sp(1La), Salpha(1Lb), Tp(3La) and Tbeta(3Bb) states. It is found that only aromatic compounds of classes IV and V can be effective scintillators and laser dyes. It is also shown that the energy interval Salpha-Sp (for class IV) and Tbeta-Sp (for class V) must be no less than 1000 cm(-1). To illustrate the classifications for heteroaromatic and aromatic compounds, 12 specifically chosen compounds were studied experimentally and quantum chemically. The quantum yields, gamma and decay times, tauf of fluorescence in aerated and non-deaerated ethanol or cyclohexane solutions were measured. The oscillator strength, f(e), fluorescence rate constant, k(f), natural lifetimes, tauT(0) and intersystem crossing rate constants, kST are calculated. The laser ability of each of the compounds studied is tested. The suggested classification schemes can be extremely useful in the quest for effective scintillators and laser dyes among hypothetical heteroaromatic and aromatic molecules, enabling evaluation of these properties for a particular compound using only quantum chemical simulations.     

The sulfonation of aromatic and heteroaromatic polycyclic compounds

Relative reactivities of a series of polycyclic carbo- and heteroaromatic compounds to sulfonation by sulfur trioxide in nitrobenzene are measured and discussed. The results show the following reactivity in decreasing order: indole, carbazole, pyrene, perylene, naphthalene, phenanthrene, benzene, benzothiophene, and dibenzothiophene.     

Electrophilic reactions of aromatic and heteroaromatic compounds in ionic liquids

The review summarizes and analyzes published data on electrophilic aromatic substitution reactions performed in ionic liquids.