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.     

Facile one-pot synthesis of aromatic and heteroaromatic sulfonamides

A series of arene and heteroarene sulfonamides were prepared in one vessel from aryl and heteroaryl bromides via conversion into the corresponding Grignard reagents using either magnesium or isopropylmagnesium chloride and subsequent reaction with sulfur dioxide, sulfuryl chloride, and an amine.     

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.     

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.     

Electrical conductivity of partly oxidized aromatic and heteroaromatic polymers

The electrical conductivity of aromatic and heteroaromatic polymers as well as polymers with aromatic, heteroaromatic and vinylene units in the main chain, can be enhanced by oxidation. In a single electron transfer reaction, a polymer with a salt structure (“doped polymer”) can be formed. Such polymers can also be prepared in a one-step reaction from low-molecular weight compounds by oxidants, as well as by electrochemical reaction. Electrochemically produced samples have higher electrical conductivities (as high as 6298K = 0,5 Ω⁻¹ · cm⁻¹) than samples made by chemical oxidation from the same starting material.     

Inter-system-crossing rate parameters of adsorbed aromatic and heteroaromatic hydrocarbons

Luminescence spectra and decay curves of phenanthrene, anthracene and l-azaphenanthrene adsorbed on thermally pretreated alumina and thoria were recorded in the temperature range of 60 – 400 K. Intersystem-crossing (ISC) rate constants were estimated and discussed with respect to the heavy-atom effect and the type of bonding to the surface. The heavy-atom enhances the radiative and non-radiative T₁--->S_O transition rates up to three powers of ten. The type of bonding only influences the thermal phosphorescence quenching rate. Its pre-expotential factor decreases by several orders of magnitude in the sequence dissolved in rigid media > physisorbed > π-complexed > σ-complexed.     

Reactions of aromatic and heteroaromatic compounds bearing electron-acceptor substituents

The specificity of the nitration and bromination of dimethyl(2-thienyl)sulfonium salts was studied. It was found that, in contrast to methyl 2-thienyl sulfide, which reacts to form 3- and 5-substituted derivatives, the sulfonium salts give a mixture of 4- and 5-substituted products. Total suppression of the activity of the position under the influence of the sulfonium grouping is not observed.See [1] for communication VIII.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 310–314, March, 1972.     

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.     

Optically active aromatic and heteroaromatic alpha-amino acids by a one-pot catalytic enantioselective addition of aromatic and heteroaromatic C-H bonds to alpha-imino esters

The development of a practical one-pot catalytic enantioselective procedure for the synthesis of non-natural aromatic and heteroaromatic alpha-amino acids is reported. Starting from readily available starting materials and application of a chiral BINAP-Cu(I) catalyst, the optically active products are formed with readily removable N-protecting groups. The scope of the reaction is demonstrated by the addition of substituted furans, thiophenes, pyrroles, and aromatic compounds to N-alkoxycarbonyl-alpha-imino esters in good yields and with enantioselectivities up to 96% ee for the furans, 93% ee for the thiophenes, and 98% for the aromatic compounds. The protecting groups are readily removed, and various transformations of the aromatic and heteroaromatic alpha-amino acids are demonstrated. The coordination of the N-alkoxycarbonyl alpha-imino ester to the chiral BINAP-Cu(I) complex and the enantioselectivity of the catalyst is discussed on the basis of the DFT calculations and X-ray crystallographic data.     

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 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.     

Halogen-magnesium exchange on unprotected aromatic and heteroaromatic carboxylic acids

The magnesiation of halogenated aromatic and heteroaromatic carboxylic acids is accomplished by their treatment with MeMgCl in the presence of LiCl and subsequent reaction with i-PrMgCl.LiCl; the resulting double-magnesiated species react with a variety of electrophiles in up to 97% yield.     

Electronic interactions in aromatic an heteroaromatic two-ring systems

The chemical shifts of the methyl protons ( ) in the PMR spectra and the integral intensities (A^1/2) of the band of the symmetrical CH stretching vibration of the methyl group in the IR spectra were measured for an extensive series of methyl derivatives of aromatic and heteroaromatic compounds including 3-, 4-, 5-, and 6-substituted 1- and 2-methylnaphthalenes, 4-, 5-, 6-, and 7-substituted 2-methylquinolines, and 5- and 6-substituted 2-methylbenzothiazoles, as well as a number of two- and three-ring systems that do not contain substituents. The changes in the chemical shifts are interpreted with allowance for two principal contributions: the contribution from the ring currents and the contribution from the changes in the electron densities (q) on the H and C atoms of the methyl group. The fact of the existence of a linear relationship between the corrected (for the ring current) values and the calculated (by the CNDO/2 method) electron charges q_C and q_H (the latter plays the dominant role) indicates that the electronic effects of the substituent make the principal contribution to the changes in the shielding constants of the protons of the methyl group in most of the investigated compounds. Similarly, the charges on the H and C atoms of the methyl group convey the trend of the integral intensities of the IR bands, thereby confirming the primarily electronic nature of the effects of structural factors on the A^1/2 values.See [2] for communication 2.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 390–396, March, 1979.     

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.