A theoretical study on the aromaticity of thiadiazoles and related compounds

Three different approaches have been considered to determinate the aromatic character of isomeric thiadiazoles. Several indices have been obtained from calculations made in the context of nonlocal (B3LYP) density functional calculations. The results were compared with the existing experimental evidence for analog heterocycles. It is concluded that the thiadiazoles are aromatic compounds, with a larger aromatic character than pyrrole, thiophene and furan. The monoxide and dioxide derivatives are shown to be non-aromatic or antiaromatic molecules.     

New method of isolating N-substituted 3-aminomethylenethiol-4-en-2-ones

The methods for the synthesis of the little-studied N-substituted 3-aminomethylenethiol-4-en-2-ones (I) — thiophene analogs of aromatic o-hydroxyazomethines — are based on the application of the not readily accessible and labile hydroxy and methoxy derivatives of thiophene [1, 2].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 854–855, June, 1986.     

Application of solid‐phase microextraction to the determination of polycyclic aromatic sulfur heterocycles in Bohai Sea crude oils

A simple and rapid solid‐phase microextraction approach for the isolation of polycyclic aromatic sulfur heterocycles from the aromatic fraction of crude oil is described. 8‐Hydroxyquinoline silica gel impregnated with palladium chloride was used as a sorbent material for extraction. Operational parameters of the extraction solvents have been evaluated and optimized. Benzothiophene, dibenzothiophene, and benzo[b]naphtho[1,2‐d]thiophene and their C₁–C₄ alkyl derivatives were identified and quantified by GC–MS. Under optimum conditions, the limits of detection for benzothiophene, dibenzothiophene, and benzo[b]naphtho[1,2‐d]thiophene were 0.277, 0.193, and 0.597 μg/g oil, respectively. The recoveries for the polycyclic aromatic sulfur heterocycles ranged from 81.5 to 92.1%, and the linear dynamic range was from 10 to 1000 ng/mL. The developed methodology was tested in the characterization of crude oil samples collected at the DY, SZ, ZH, and HC petroleum oil fields of the Bohai Sea. The results proved that SPE coupled with GC–MS is a promising tool for the quantitative analysis of polycyclic aromatic sulfur heterocycles in crude oils, especially for oil samples with low concentrations of polycyclic aromatic sulfur heterocycles.     

Preparation and new transformations of trichloromethyl-substituted aliphatic,aromatic, and heterocyclic compounds (review)

A summary is given for new syntheses of heterocycles starting with trichloromethylarenes and the readily available products of the addition of carbon tetrachloride to functional derivatives of olefins. Applications of the electrophilic trichloromethylation for benzene and thiophene compounds are considered. Information is given on the reactions of trichloromethylarenes with heteronucleophiles, in particular, leading to the synthesis of diaryl-1,2,4- and diaryl-1,3,4-oxadiazoles. The reaction of trichloromethylarenes and pyridines to give the corresponding aromatic aldehydes and N-(4-pyridyl)pyridinium dichloride is discussed.Dedicated to Professor A. R. Katritzky on the occasion of his sixty-fifth birthday.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 980–990, July, 1993.     

Cross-metathesis of vinyl aromatic heterocycles with 1-octene in the presence of a Schrock catalyst

Metathesis of 2-vinyl aromatic heterocycles such as furan, thiophene, pyrrole and pyridine in the presence of a molybdenum-based Schrock catalyst has been investigated from a synthetic point of view. The self-metathesis of 2-vinyl aromatic heterocycles was not successful. However, in cross-metathesis of thiophene, furan and styrene with 1-octene, the cross-metathesis product, heterodimer, was readily obtained selectively, together with only small amounts of the two corresponding self-metathesis products. The origin of the surprisingly high selectivity of heterodimer formation was elucidated through metallacyclobutane intermediate mechanism, observations of carbenes by in situ ¹H NMR, and reaction products.     

Cross-metathesis of vinyl aromatic heterocycles: comparison of Grubbs catalyst and Schrock catalyst

Metathesis of 2-vinyl aromatic heterocycles such as furan and thiophene has been investigated in the presence of a ruthenium-based Grubbs catalyst from a synthetic standpoint. The self-metathesis of 2-vinyl aromatic heterocycles was not successful. However, the cross-metathesis of these aromatic heterocycles with 1-octene occurred efficiently, but the selectivity of cross-metathesis product was very low, below 50%. The origin of the low selectivity of heterodimer formation was elucidated through metallacyclobutane intermediate mechanism, observations of carbenes by in situ ¹H NMR, and the reaction products. The effect of oxygen on the reaction behavior was also examined. Furthermore, the data obtained on the Grubbs catalyst were compared with those on a molybdenum-based Schrock catalyst.     

Reaction of 2-methyl-3-ethoxycarbonyl-4-hydroxythiophene with hydrazines

2-Methyl-3-ethoxycarbonyl-4-(N,N-dimethylhydrazino)thiophene (II) and 2-methyl-3-ethoxy-carbonyl-4-(N-phenylhydrazino)thiophene (III) are formed by the action of substituted hydrazines — N,N-dimethylhydrazine and phenylhydrazine — on 2-methyl-3-ethoxycarbonyl-4-hydroxythiophene (I). At the same time, the thiophene ring of hydroxythiophene I undergoes hydrazinolysis under the influence of hydrazine hydrate to form 3-mercaptomethyl-4-ethoxycarbonyl-5-methylpyrazole (IV). Structure IV was proved by IR, UV, and PMR spectroscopy and by hydrogenolysis of IV to the known 3,5-dimethyl-4-ethoxycarbonylpyrazole (V).Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 759–761, June, 1971.     

Comparison of Thiophene–Pyrrole Oligomers with Oligothiophenes: A Joint Experimental and Theoretical Investigation of Their Structural and Spectroscopic Properties

We have prepared a new series of mixed thiophene–pyrrole oligomers to investigate the electronic benefits arising from the combination of these two heterocycles. The oligomers are functionalized with several hexyl and aryl groups to improve both processability and chemical robustness. An analysis of their spectroscopic (absorption and emission), photophysical, electrochemical, solid state, and vibrational properties is performed in combination with quantum‐chemical calculations. This analysis provides relevant information regarding the use of these materials as organic semiconductors. The balance between the high aromatic character of pyrrole and the moderate aromaticity of thiophene allows us to address the impact of the coupling of these heterocycles in conjugated systems. The data are interpreted on the basis of the aromaticity, molecular conformations, ground and excited electronic state structures, frontier orbital topologies and energies, oxidative states, and quinoidal versus aromatic competition.     

Thermal methods for the synthesis of thiophene, selenophene, and their derivatives. (Review)

The literature data concerned with thermal reactions producing thiophene, selenophene, and their derivatives are systematized and reviewed. The mechanisms of these reactions are examined and conditions for the formation of thiophene and selenophene heterocycles are formulated.Irkutsk Institute of Chemistry, Siberian Branch, Russian Academy of Sciences, Irkutsk 664039, Russia; e-mail: vlad@irioch.ira.ru. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 3–18, January, 2000.     

Deuteration of molecules for neutron reflectometry on organic light-emitting diode thin films

Deuterated forms of aromatic charge transporting heterocycles 2 and 3 used in organic light-emitting diodes have been produced by hydrothermal reactions, catalyzed by Pt/C or Pd/C. Comprehensive analysis by mass spectroscopy, ¹H, ²H and ¹³C NMR enables determination of the overall quantity of D atoms present, as well as the level of deuteration at each molecular site. The roles of solubility and steric availability in deuteration are discussed in the light of these results. Neutron reflectometry indicates excellent scattering contrast between protonated and deuterated forms of these molecules, with nanoscale thin films showing the same density as in their bulk molecular forms. Although used for morphological studies of thin films typically used in OLEDs, the synthetic and analysis methods described here are generic and suitable for deuteration of other conjugated aromatic heterocycles and other optoelectronic devices.     

HIGH TEMPERATURE REACTIONS OF HYDROGEN SULFIDE AND THIOLS WITH ORGANIC COMPOUNDS

Abstract

The high temperature reaction of hydrogen sulfide with chloro- and bromosubstituted aromatic and heteroaromatic compounds is a convenient method for synthesis of the corresponding thiols and sulfides. The reaction of hydrogen sulfide with ortho-dihalosubstituted aromatic compounds may be directed toward the formation of thianthrene or dibenzo thiophene and their derivatives. The high temperature reaction of thiophenol with chloro- and bromoderivatives of aromatic and heteroaromatic compounds affords the corresponding mixed sulfides. The reaction with ortho-substituted halogen derivatives leads to formation of the sulfur heterocycles of the thianthrene, thioxanthene and dibenzothiophenene series.

The high temperature reaction of hydrogen sulfide with vinyl chloride gives vinylthiol and thiophene. Hydrogen sulfide initiates pyrolytic transformations of thiophene, aniline and benzaldehyde into dithienyls, 5.10-dihydrophenazine and stilbene, respectively. The reaction mechanism has been discussed.     

Study on the nature of interaction of thiophene with various hydrides

The nature of interactions of thiophene with various hydrides (Y) (Y = HF, HCl, H₂O, H₂S, NH₃, PH₃) is investigated using ab initio calculations. In contrast with the previous results on similar furan complexes, only the π-type is observed for the thiophene complexes. Variations in complexes geometry can be accounted for by the differences in the electrostatic potential on the aromatic ring. To further study the nature of the intermolecular interactions, an SAPT (the symmetry-adapted perturbation theory) energy decomposition analysis was carried out and the results indicate that the dispersion and electrostatic interactions dominate the thiophene complexes.     

Effect of acceptor heteroatoms on π-hydrogen bonding interactions: A study of indole⋅⋅⋅thiophene heterodimer in a supersonic jet

Resonant two photon ionization (R2PI), IR-UV, and UV-UV double resonance spectroscopic techniques combined with quantum chemistry calculations have been used to determine the structure of indole???thiophene dimer observed in a supersonic jet. With the help of combined experimental and theoretical IR spectra it has been found that the observed dimer has a N-H???π hydrogen bonded slanted T-shaped structure. The present study demonstrates the effect of heteroatoms present in the acceptors on the strength of the π-hydrogen bonding interactions. It was concluded by Sherrill and co-workers from their theoretical study of benzene???pyridine dimer that aromatic rings containing heteroatoms are poorest π-hydrogen bond acceptors [E. G. Hohenstein and C. D. Sherrill, J. Phys. Chem. A 113, 878 (2009)]. But the current spectroscopic investigation exhibits that five membered aromatic heterocycles are favorable π-hydrogen bond acceptors. In this study, it has also been shown that thiophene is a better π-hydrogen bond acceptor than furan. The present work has immense biological significance as indole is the chromophore of tryptophan residue in the proteins and thiophene derivatives have potential therapeutic applications. Thus, understanding the binding motif between indole and thiophene in the heterodimer studied in this work may help in designing efficient drugs.     

Synthesis of 2-methylthie no [3,2-b]thieno-[2,3-d]thiazole

A new heterocyclic base — 2-methylthieno[3,2-b]thieno[2,3-d]thiazole — was synthesized by heating 2-acetamido-3-hydroxythieno[3,2-b]thiophene with phosphorus pentasulfide.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1039–1041, August, 1976.     

Autooxidation of methylheterocycles under phase transfer catalysis conditions

The autooxidation of methyl- and dimethyl-substituted N-, S-, and O-heterocyclic compound derivatives has been studied in 1,2-dimethoxyethane—t-BuOK in the presence of 18-crown-6. Mono- and dicarboxylic acid derivatives of pyrazine, pyridine, pyrimidine, and thiophene have been synthesized.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 959–962, July, 1991.     

Rare‐Earth‐Catalyzed C−H Silylation of Aromatic Heterocycles with Hydrosilanes

The catalytic C?H silylation of a variety of aromatic heterocycles such as furan, pyrrole and thiophene derivatives with secondary hydrosilanes has been achieved by using an yttrium metallocene complex. This protocol provides an efficient and straightforward way for the synthesis of a series of silylated heteroaromatic compounds containing tertiary silane moieties without the need for an additive or H₂ acceptor.     

Reactions of benzo-1,2,3-dithiazolium salts and their selenium analogs with amines

The corresponding 6-arylamino derivatives were obtained by reaction of 6-chloro, 6-bromo, and 6-methoxy derivatives of benzo-1,2,3-dithiazolium and their selenium analogs — benzo-1,2,3-thiaselenazolium, benzo-2,1,3-thiaselenazolium, and benzo-1,2,3-diselenazolium salts — with aromatic amines. The 6-methoxy derivatives also react with acetates of secondary aliphatic amines, whereas in the case of the chloro derivatives attack is directed to the heteroring. 6-Aryl(dialkyl)amino derivatives of dithiazolium and 1,2,3-thiaselenazolium salts are protonated in concentrated sulfuric acid at the exocyclic nitrogen atom. The analogous derivatives of 2,1,3-thiaselenazolium and diselenazolium salts under the same conditions form a tautomeric mixture of dications, the position of the equilibrium between which depends on the substituent. The electronic and PMR spectra of the amination products are presented.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1499–1502, November, 1977.     

Basicity and structure of α, β -unsaturated heterocyclic ketones

The protolytic equilibrium constants of chalcone and its furan and thiophene analogs have been measured spectrophotometrically in sulfuric acid — glacial acetic acid solution. It is shown that the furan ketones are more basic than the thiophene ones, basicity depending on the position of the carbonyl group in the conjugated chain. In the systems studied, 2-furyl exhibits an appreciably greater positive dynamical conjugation effect than 2-thienyl, but as compared with the latter it gives rise to less steric hindrance to solvation of carbonium ions.For Part II see [2].     

A semiempirical study of heterocycle oligomers and polymers in different dielectric media

Four common five-membered heterocycles—pyrrole, phosphole, thiophene, and furan—and their oligomers with the chain length of 2, 4, 6, and 10 units have been studied quantum chemically using the semiempirical PM 3 parameterization. The oligomers of pyrrole and phosphole with the homolytically dissociated N? H bond and P? H bond, respectively, and oligomers of thiophene and furan with one electron removed per monomer unit (4n + 2 π-electron bipolaron systems) have also been studied. The electronic properties of the respective polymers were extrapolated from the oligomer data. Bulk polymer effects on the electronic structure were modeled using the self-consistent reaction field theory in the multicavity approximation (MC a SCRF ). © 1995 John Wiley & Sons, Inc.     

Ring-chain isomerism (tautomerism) of functionally substituted hydrazones (review)

The known data on the ring-chain tautomerism (isomerism) of hydrazones with functional substitutents in the alkylidene or hydrazine fragment of the molecules are systematized. The structural factors and conditions that determine the reversible conversion of the corresponding linear derivatives to representatives of heterocycles — isoindole, tetrahydrofuran, pyrazole, isoxazole, 1,2,4-triazole, 1,3,4-thiadiazole, 1,3,4-oxadiazine, 1,2,4-triazine, 1,3,4-thiadiazine, 1,2,4,5-tetrazine, etc. — are correlated.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 3–19, January, 1988.