Activity and selectivity in the electrophilic substitution of five-membered heterorings (review)

Data on the activity and selectivity in reactions involving the electrophilic substitution of five-membered heteroaromatic compounds with one heteroatom are discussed. Chief attention is directed to the reactions of pyrrole, furan, thiophene, and their substituted derivatives. The inconsistency in the change in the activity (reaction rate) — N>O>S — and in the positional selectivity (the ß ratio) — N相似文献   

A Quantum Chemical Study of N14 Cluster

Ab initio molecular orbital theory and density functional theory have been employed to study N₁₄ cluster with low spin at the HF/6-31G*, B3LYP/6-31G*, B3PW91/6-31G*, BP86/6-31G*, and BHLYP/6-31G* levels of theory. Twelve isomers were studied, including one previously investigated cage molecule. The most stable isomer of N₁₄ is a C _2h -symmetric molecule that contains two separated five-membered nitrogen rings connected by a —N=N—N=N— bridge. The second, third, and fifth most stable isomers each have one five-membered nitrogen ring. The theoretical results suggest that the five-membered nitrogen ring gives rise to a particularly stable structural unit, and the more side chains that the five-membered nitrogen ring links with, the less stable the structure will become.     

Effect of the heteroatom on the energies of the boundary molecular orbitals of dibenzo derivatives of five-membered heterocycles

The effect of the heteroatom on the energy characteristics of their boundary molecular Orbitals was studied by investigation of the charge-transfer complexes (CTC) of the dibenzo derivatives of five-membered heterocycles. Tetramethyl-substituted dibenzo derivatives of five-membered heterocycles were investigated as electron donors, and their corresponding dianhydrides were investigated as electron acceptors. Their ionization potentials and electron affinities, respectively, were determined. From the regularities in the change in these characteristics it was concluded that replacement of one heteroatom by another leads to approximately identical energy shifts of both boundary molecular orbitals.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 185–187, February, 1979.     

Thermodynamic analysis of strain in the five-membered oxygen and nitrogen heterocyclic compounds

Cyclopentane is conventionally strained. Replacement of a carbon atom by a heteroatom obviously impacts angular strain in the five-membered ring compounds. Changes of strains in the five-membered cycles are also caused by a double bond or atttached benzene rings. We studied the thermochemical properties of Indane, 2,3-dihydrobenzofuran, indoline, N-methyl-indoline, carbazole, and N-ethyl-carbazole to obtain a better quantitative understanding of the energetics associated with these compounds containing five-membered ring units. We used combustion calorimetry, transpiration method, and high-level first-principles calculations to derive gaseous enthalpies of formation of the five-membered heterocyclic compounds. Our new values together with the selected values for parent heterocyclic compounds, available from the literature, were used for calculation of the strain energies H(S) of five-membered C-, N-, and O-containing cycles. Quantitative analysis of the resulting stabilization or destabilization of a molecule due to interaction of benzene rings with the heteroatom has been performed.     

Synthesis of 2H-imidazole 1-oxides and stable nitroxyl radicals based on them

2H-Imidazole 1-oxides containing an aldonitrone group in the heterocyclic ring are obtained by the condensation of hydroximinomethyl ketones with ketones and ammonium acetate. Their oxidation with lead dioxide in methanol gives stable nitroxyl radicals — 5,5-dimethoxy-3-imidazoline-1-oxyls.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2113–2121, September, 1991.     

Template reactions of fluorine-containing 1,3-diketones with ethylenediamine

Depending on the nature of the dicarbonyl fragment, the reaction of fluorinated copper(II) bis(1,3-diketonates) with ethylenediamine and its monoprotonated salts under mild conditions gives N,N-ethylenebis(aminovinyl ketones) and/or 1,4-diazepines. In excess ethylenediamine, copper(II) and nickel(II) N,N-ethylenebis(aminovinyl ketonates) undergo cyclization to 1,4-diazepines.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2088–2092, September, 1991.     

Aminovinyl ketones and aminovinyl esters as CCN building blocks for the synthesis of 1H-pyrrolo[3,2-e]1,2,4-triazines

5,6-Unsubstituted-3-aryl-1,2,4-triazines were found to react with aminovinyl ketones and aminovinyl esters in acetic anhydride to form derivatives of 3a,4,7,7a-tetrahydro-1H-pyrrolo[3,2-e]1,2,4-triazines in good yields.     

The direction of the dipole moments of furan,thiophen, and pyrrole: A controversial question

The report that the dipole moment in the five-membered heterocyclic rings, furan, thiophene, and pyrrole has the positive pole on the heteroatom is contradicted with arguments based on reactivity data, theoretical calculations and moment values of substituted derivatives. In actuality, the dipole moment in furan and thiophene is directed from the ring (positive pole) to the heteroatom (negative pole).     

Synthesis of dihydrothieno[3,4-b]indoles

A new heterocyclic system — 3-imino-4-methyldihydrothieno[3,4-b]indole — was obtained by treatment of 1-methylindole-2-carboxylic acid thioamide with aldehydes or ketones in the presence of hydrogen chloride. Reactions involving saponification and acetylation of the imino group of the thieno ring and opening of the thieno ring by the action of LiAlH₄ to give a bis(indolylphenylmethyl) sulfide were carried out. A scheme is proposed in which the SH group of the thioamide adds to the carbonyl compound in the first step, after which the product undergoes intramolecular cyclization in the 3 position of indole.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1327–1331, October, 1977.     

Synthesis and some transformations of pyrroles with aliphatic acyl substituents

A number of higher aliphatic pyrryl ketones were synthesized. It is shown that a carbethoxy group in the 5 position of the pyrrole ring relatively weakly deactivates the 3 position of the ring to electrophilic attack during Friedel—Crafts acylation but hinders this reaction considerably when it is in the adjacent 4 position. The oxidation of the -methyl group in a series of pyrryl ketones and the corresponding alcohols was studied.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 27–30, January, 1973.     

Thermodynamic analysis of strain in heteroatom derivatives of indene

Thermochemical properties of indene, 2,3-benzofuran, indole, and N-methylindole have been studied to obtain a better quantitative understanding of the energetics associated with these compounds containing five-membered ring units. We used combustion calorimetry, transpiration, and high-level first-principles calculations to derive gaseous enthalpies of formation of the five-membered heterocyclic compounds. Our new values together with selected values for the parent heterocyclic compounds, available from the literature were used for calculation of the strain enthalpies H(S) of five-membered C, N, and O-containing cycles. The quantitative analysis of the resulting stabilization or destabilization of a molecule due to interaction of the benzene ring with the heteroatom has been performed.     

Transformations of 2-methylthiacyclobutane in the presence of aluminum oxide

The transformations of 2-methylthiacyclobutane at 150–350 °C in the presence of -Al₂O₃ samples with different aprotic acidities were investigated. It was established that the sulfide undergoes isomerization via two pathways, viz., with ring expansion to a five-membered ring and with opening at one C—S bond to give an unsaturated thiol. An experimental confirmation of the consecutive formation of hydrogen sulfide from a one-ring sulfide through a step involving the formation of an unsaturated thiol was obtained for the first time. The transformations are realized as a result of both ionic and polymerization-depolymerization processes.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 184–187, February, 1982.     

Benzoid-quinoid tautomerism in azomethines and their structural analogs. 46. Synthesis and reactions of 2-(N-isatinomethylene)-3(2H)-benzo[b]thiophenone

Electronic, IR and UV spectroscopy has shown that 2-(N-isatinomethylene)-3(2H)-benzo[b]thiophenone in solution displays photo- and solvatochromism as a result of reversible E Z isomerization, and it readily undergoes alcoholysis of the lactam bond. The resulting aminovinyl ketones exist as mixtures of the thermodynamically stable E- and Z-isomers.For Communication 45, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1217–1220, September, 1989.     

Investigation of the stereochemical direction of the cyanoethylation of six-membered heterocyclic ketones as a function of the nature of the heteroatom

Only a mono (cyanoethyl) compound is formed from thiopyranone in the cyanoethylation of six-membered heterocyclic ketones that contain a methyl group attached to the C₂ atom of the heteroring, whereas primarily bis- and tris(cyanoethyl) derivatives are obtained from pyranone due to the effect of the heteroatom.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1342–1343, October, 1982.     

N-Vinyl as N-H protecting group. Synthesis of cyclic imines from N-vinyllactams and organolithium reagents

On reaction with organolithium reagents followed by hydrolysis and distillation, N-vinylpyrrolidone ( 1 ) gives five-membered ring imines 3-8 , whereas N-vinylcaprolactam ( 2 ) gives mixtures of seven-membered ring imines and the corresponding ∈-amino ketones.     

The explicit interactions of five-membered saturated heterocyclics containing one and two heteroatoms with single water molecule

In this article, the hydrogen bonding interaction between saturated five-membered heterocyclic molecules and water has been investigated. Molecular orbital and density functional theory methods have been used to evaluate the stabilization energies associated with the adduct formation between heterocyclic molecules and water. The hydrogen bond acceptor ability of O, S, Se, and N as members of five-membered ring has been analyzed. The effect of the presence of second heteroatom N in the ring on the hydrogen bond interaction has also been evaluated. Atoms in molecules theory calculations were carried out to characterize the hydrogen bond through the changes in electron density and Laplacian of electron density. A natural energy decomposition analysis and natural bond orbital analysis is also performed to understand the nature of hydrogen bonding interaction in monohydrated five-membered heterocyclic adducts.     

Asymmetric synthesis of α-chiral ketones by the reduction of enones with baker's yeast

Baker's yeast-mediated asymmetric reduction of α,β-unsaturated ketones (enones) having a pyridyl ring affords the corresponding optically active α-substituted ketones (α-chiral ketones) with excellent stereoselectivity. The position of the heteroatom, as well as the bulk of the α-substituent, plays an important role in governing the stereoselectivity in the reduction of a carboncarbon double bond.     

Substitution in a number of five-membered heterocycles with one heteroatom catalytic alkylation of N-methylpyrrole and thiophene with olefins

It has been found that a decrease in the yield of -substituted products during alkylation with olefins is observed in a number of five-membered heterocycles (furan, thiophene, and N-methylpyrrole). The change in the -orienting effect depends not only on the nature of the heteroatom but also on the type of reaction and on the conditions of the process. In the case of N-methylpyrrole, the possibility of C-alkylation of the pyrrole ring with olefins was demonstrated for the first time.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 502–506, April, 1973.     

Regioselective C-H Functionalization of the Six-Membered Ring of the 6,5-Fused Heterocyclic Systems: An Overview

The regioselective C-H functionalization of the five-membered ring of the 6,5-fused heterocyclic systems is nowadays well documented due to its high reactivity compared to the six-membered ring. So, developing new procedures of C-H functionalization of the six-membered ring “by thinking out of the box” is extremely challenging, which explains the limited number of reports published to date. This review paper aims to highlight advances achieved in this emerging chemistry research and discusses recently reported methods.     

Synthesis of indoles from pyridinium salts 5. Secondary amines in the reaction of 3-nitropyridinium salts with acetone

The use of secondary amines in the reaction of 3-nitropyridinium salts with acetone makes it possible to isolate stable intermediates in the formation of indoles — (o-N,N-dialkylaminobenzyl)ketones — and to observe new reaction pathways — the formation of bisindolylpropanes and p-nitroanilines.See [1] for Communication 4.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1213–1221, September, 1988.