Relative Stabilities of Hetarenium Ions: Factors Controlling Positional Selectivities of Electrophilic Substitution and Acid-induced Transformations of Pyrrole, Furan and Thiophene Derivatives

Belenkii, L. I.; Беленький, Л. И.

doi:10.3987/rev-93-sr16

Cited by 39 publications

(11 citation statements)

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“…In interpreting these results it seems appropriate to take into account the possible steric influence of the npropyl group impeding the substitution at the α-position of the pyrrole ring. 36 The structures of tricyanovinyl-substituted pyrrole derivatives 1 were unambiguously confirmed by their analytical and spectral data. In the 1 These signals were attributed respectively, to the 4', 3' and 5'-H protons in the thiophene moiety.…”

Section: Synthesismentioning

confidence: 75%

“…[34][35][36][37][38] The reactivity of these systems has been demonstrated with the use of electrophilic reactions producing derivatives with the electrophile substituted primarily on the pyrrole ring. [37][38][39][40][41][42][43][44] Accordingly, tricyanovinylation of thienylpyrroles 2 proceeded selectively in the pyrrole ring to form the corresponding tricyanovinyl-substituted thienylpyrroles 1.…”

Section: Synthesismentioning

confidence: 99%

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Synthesis of tricyanovinyl-substituted thienylpyrroles and characterization of the solvatochromic, electrochemical and non-linear optical properties

et al. 2005

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-Tricyanovinyl-substituted 1-(alkyl)aryl-2-(2´-thienyl)pyrroles 1 have been synthesized by direct tricyanovinylation reaction of 1-(alkyl)aryl-2-(2´-thienyl)pyrroles 2 using TCNE. The tricyanovinyl-derivatives 1 display dramatic reductions in both their optical and electrochemical band gaps relative to thienylpyrrole precursors 2. The solvatochromic behavior of compounds 1 was investigated in a variety of solvents. Hyper-Rayleigh scattering was used to measure the first hyperpolarizabilities β of the mentioned compounds. The β values show that the new compounds prepared could be used on the manufacture of materials with good non-linear (NLO) properties.

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Section: Synthesismentioning

confidence: 75%

Section: Synthesismentioning

confidence: 99%

Synthesis of tricyanovinyl-substituted thienylpyrroles and characterization of the solvatochromic, electrochemical and non-linear optical properties

et al. 2005

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“…We presumed in [1,[7][8][9] that substituent on the nitrogen atom could affect the α : β ratio via stabilization (electron-donor groups) or destabilization (electron-withdrawing groups) of the corresponding onium species. This is confirmed by the following examples.…”

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confidence: 99%

Quantum-Chemical Study on Positional Selectivity in the Trimethylsilylation and Sulfonation of Pyrrole and N-Alkylpyrroles

et al. 2005

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Positional selectivity (α : β ratio) of electrophilic substitution in pyrrole, N-methylpyrrole, and N-tert-butylpyrrole was analyzed by ab initio , MP2/6-31G(d)//RHF/6-31G(d)] and DFT [B3LYP/6-31G(d)] calculations of some σ-complexes derived from the substrates. The results of calculations with the use as model electrophilic species of trimethylsilyl cation [MP2/6-31G(d)//RHF/6-31G(d) and B3LYP/6-31G(d)] and SO 3 molecule [B3LYP/6-31G(d)] instead of proton are fairly consistent with the experimental data, according to which trimethylsilylation of pyrrole and its N-substituted derivatives with trimethylsilyl trifluoromethanesulfonate, as well as sulfonation with pyridine-sulfur trioxide complex, gives the corresponding β-substituted products.We previously performed a quantum-chemical study on positional selectivity in electrophilic substitution in derivatives of pyrrole, furan, thiophene, selenophene, and their benzo-fused analogs [1]. Our results allowed us to rationalize the absence of correlation between the reactivity (substrate selectivity) and positional selectivity (ratio of the α-and β-substituted products). Very strong differences in the reactivity (in the series pyrrole >> furan > selenophene > thiophene the reactivity decreases by about 10 orders of magnitude) may be interpreted in terms of different conditions for electron density delocalization over the ring atoms in intermediate σ-complexes (primarily in more thermodynamically favorable ionic species like A), which involves overlap of carbon π-orbitals with n-orbitals of heteroatoms belonging to different groups and periods of the Periodic Table (Scheme 1) [2,3]. However, the selectivity (α : β) conformed to a different series: furan > selenophene > thiophene > pyrrole, which was not rationalized so far. The results of our ab initio [RHF/6-31G(d), MP2/6-31G(d)//RHF/6-31G(d)] and DFT [density functional theory; B3LYP/6-31G(d)] calculations of pyrrole, furan, thiophene, and selenophene molecules, as well as of the corresponding benzo-fused systems and hetarenium ions formed upon protonation (E = H) [1], were consistent with our previous hypothesis [4, 5] implying predominant contribution of heteroatoms to the stabilization of σ-com-

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“…It was suggested in [46,47] that the stability of the 3H-hetarenium ions B corresponding to β-substitution, where the positive charge is distributed between two atoms (the heteroatom and atom C(2)), depends on the effect of the heteroatom to a larger degree than in the case of α substitution (cation A) where three ring atoms formally participate in delocalization of the positive charge; here the variation of the relative stability of the 3H-hetarenium ions in relation to the nature of the heteroatom must be similar to the variations found in onium compounds (N + > S + > O + ) and must correspond to the observed decrease in the content of the β-isomers in the order: pyrrole > thiophene >furan Subsequently, the ratio of the activity and selectivity in the electrophilic substitution reactions of fivemembered heteroaromatic compounds has been the subject of extensive quantum-chemical investigations by the CNDO/2 method [48][49][50][51] and in later years by the B3LYP/6-31G(d) method of density functional theory and the nonempirical RHF/6-31G(d) and PM2/6-31G(D) methods [52][53][54][55][56][57][58][59][60][61]. The calculations by the semiempirical CNDO/2 method [48] gave values for the differences in the energies of the cations formed during protonation at the α-and β-positions (ΔE α-β ) that corresponded to existing experimental data on the order of variation of the positional selectivity: furan > thiophene > pyrrole.…”

Section: The Electron Structure the Relative Stability Of The Intermmentioning

confidence: 97%

Development of quantum-chemical investigations of heterocycles at the Institute of Organic Chemistry, Russian Academy of Sciences (review)

Беленький

Чувылкин

2011

Chem Heterocycl Comp

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of attack by electrophile (position selectivity), relative stability of onium ions, stable thiophenium ions, their transformations.This review is dedicated to the memory of the distinguished organic chemist, one of the "founding fathers" of the journal "Chemistry of Heterocyclic Compounds", Professor, Doctor of chemical sciences, eminent man of science and technology of the RSFSR Ya. L. Gol'dfarb. As a scientist Prof. Gol'dfarb invariably showed a keen interest in all that was new and progressive in science, and the last 30 years of Yakov Lazarevich's life, when instrumental methods and theoretical concepts were being vigorously developed, were exceptionally prolific. It is no wonder that even in 1970-1971 Ya. L. Gol'dfarb became the initiator of the use of quantum-chemical methods in work at the synthesis laboratories of the N. D. Zelinsky Institute of Organic Chemistry. The possibilities of quantum-chemical methods have certainly increased substantially over the last 40 years, but the pioneering work still retains its significance in that appropriate models were carefully selected and the results of the calculations were always matched with the experimental data.Typically, the quantum-chemical calculations were no way to "dress up" the work carried out in the laboratory but were directed toward a meaningful study of the reactivity of heteroaromatic compounds, and to this day investigations are conducted with close collaboration between specialists in organic synthesis and specialists in the field of quantum chemistry. It is no coincidence that even in 1972 experimental data existing at that time on the reactivity and structure of compounds of the thiophene and furan series carrying electronaccepting substituents were being analyzed in detail on the basis of the results of quantum-chemical calculations performed at the Institute of Organic Chemistry, USSR Academy of Sciences [1], while in1977 the _______ * In happy memory of Yakov Lazarevich Gol'dfarb.

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Relative Stabilities of Hetarenium Ions: Factors Controlling Positional Selectivities of Electrophilic Substitution and Acid-induced Transformations of Pyrrole, Furan and Thiophene Derivatives

Cited by 39 publications

References 0 publications

Synthesis of tricyanovinyl-substituted thienylpyrroles and characterization of the solvatochromic, electrochemical and non-linear optical properties

Synthesis of tricyanovinyl-substituted thienylpyrroles and characterization of the solvatochromic, electrochemical and non-linear optical properties

Quantum-Chemical Study on Positional Selectivity in the Trimethylsilylation and Sulfonation of Pyrrole and N-Alkylpyrroles

Development of quantum-chemical investigations of heterocycles at the Institute of Organic Chemistry, Russian Academy of Sciences (review)

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