Synthesis of benzo-fused five- and six-membered heterocycles by palladium-catalyzed cyclocarbonylation

A novel and simple synthetic methodology, based on palladium-catalyzed cyclocarbonylation reaction, is presented for preparing five- and six-membered benzo-fused heterocycles. A mechanism for the process is also proposed and discussed.     

Substituent effects and aromaticity of six-membered heterocycles

Structure, aromaticity, relative stability, and conformational flexibility of nitro and amino substituted monoheterocyclic analogous of benzene were studied by ab initio quantum-chemical method at MP2/aug-cc-pvDZ level of theory. Amino derivatives were found to be slightly less aromatic than nitro derivatives. Strong push–pull interactions were found in α- and γ-aminochalcogenopyrylium cations and, in less extent, in α- and γ-aminopyrydines. These molecules are less aromatic but more stable, as compare to their β-isomers. All heterocycles with 3rd and 4th row heteroatoms reveal C–NO₂ bond elongation accompanied by C–Heteroatom bond shortening in β-nitro isomers, and strong inequality of two endocyclic C–Heteroatom bonds in α-amino isomers.     

Synthesis and characterisation of four- and six-membered P-Se heterocycles

The preparation, spectroscopic characterisation and crystal structures of [FcP(mu-Se)Se]2, [FcP(mu-Se2)Se]2 and [PhP(mu-Se2)Se]2 are reported. Crystallographic data reveal planar four-membered PSePSe and skewed six-membered P2Se4 rings, respectively, in all cases with trans arrangement of organic substituents and exo selenium atoms. Whilst stable at room temperature in solid state, NMR data suggest the six-membered rings of both the ferrocenyl and phenyl compounds decompose in the solution with loss of red selenium, forming PSe2PSe five-membered rings.     

Sequential N-acylamide methylenation-enamide ring-closing metathesis: construction of benzo-fused nitrogen heterocycles

The dimethyltitanocene methylenation of N-acylamides derived from ortho-vinylanilines, ortho-allylaniline, and ortho-vinylbenzylamine provides the corresponding enamides, which upon exposure to the second generation Grubbs ruthenium catalyst give access to indoles, 1,4-dihydroquinolines, and 1,2-dihydroisoquinolines, respectively. This sequential protocol also allows the synthesis of dihydrobenzoazepines, although the ring-closing metathesis (RCM) step is complicated by the alkene isomerization processes. From certain substrates, the direct annulation is observed in the titanium-mediated step, which is likely to occur through an olefin metathesis-intramolecular olefination sequence.     

Ring-closing metathesis for the synthesis of novel 9- and 10-membered silicon-containing benzo-fused heterocycles

A ring-closing metathesis (RCM) strategy afforded a number of novel 9- and 10-membered benzo-fused compounds containing at least one silicon atom as part of the heterocyclic portion. In this manner, the following compounds containing heterocyclic rings of 9-10 atoms were synthesized: (Z)-2,2-dimethyl-7-[(4-methylphenyl)sulfonyl]-2,3,6,7-tetrahydrobenzo[h][1,7,2]oxazasilonine, (Z)-2,2-dimethyl-3,6-dihydro-2H-benzo[h][1,7,2]dioxasilonine, (Z)-8-isopropoxy-9-methoxy-3,3-dimethyl-1,3,4,7-tetrahydrobenzo[g][1,2]oxasilonine and (Z)-2,2,7,7-tetramethyl-2,3,6,7-tetrahydrobenzo[i][1,8,2,7]dioxadisilecine.     

Synthesis of unsaturated 1,4-heteroatom-containing benzo-fused heterocycles using a sequential isomerization-ring-closing metathesis strategy

A small library of 1,4-benzodioxins and 4H-1,4-benzoxazines was synthesized from the corresponding bis-allyloxy precursors by way of an initial isomerization to the bis-vinyloxy compounds, followed by a ring-closing metathesis using the second generation Grubbs' catalyst (G2). A related strategy, starting from benzene-1,2-dithiol and 2-mercaptophenol, afforded benzodithiin and 1,4-benzoxathiin, respectively.     

The application of a new aromaticity index to six-membered ring heterocycles

A previously described index of aromatic character has now been applied to six-membered ring heterocycles. Of particular interest is its ability to indicate the extent of aromatic character retained by the amide form of potential hydroxyheterocycles.     

A synthesis of aromatic five- and six-membered B-N heterocycles via ring closing metathesis

The ring closing metathesis on appropriate vinyl or allyl aminoboranes (1 or 2) gives azaboracycloalkenes (3 or 4) which can be converted to azaborolides (5) or azaborines (6).     

Recent developments in the synthesis of five- and six-membered heterocycles using molecular iodine

Heterocyclic scaffolds represent the key structural subunits of many biologically active compounds. Over the last few years iodine-mediated reactions have been extensively studied due to their low cost and eco-friendliness. This Review covers advances in the field of iodine-mediated synthesis of heterocyclic compounds since 2006, especially with an emphasis on mechanisms of ring formation. In this article, syntheses of different heterocycles are classified based on the manipulation of functional groups.     

Quantum-chemical interpretation of recyclization reactions. 10. Photoisomerization of six-membered heterocycles

Singlet photoisomerizations of a number of six-membered heterocycles have been described on the basis of the index approach in the framework of the coupled variant of perturbation theory for a one-electron transition density matrix in the Pariser-Parr-Pople method.For Communication 9, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 357–363, March, 1986.     

Oxidation of p-aminophenols and formal radical cyclization onto benzene rings: formation of benzo-fused nitrogen heterocycles

p-Iodophenol and its O-MOM-protected ether can be converted into iodoamines 2. These give cross-conjugated ketones 3 on oxidation with hypervalent iodides in the presence of methanol, and the ketones undergo radical cyclization. Exposure of the products to acid or sequential treatment with a Grignard reagent and acid effects rearomatization to produce benzo-fused nitrogen heterocycles 4.     

Sequential isomerization and ring-closing metathesis: masked styryl and vinyloxyaryl groups for the synthesis of benzo-fused heterocycles

The use of an aryl allyl ether and an arylallyl group as masked vinyl ether and 1-propenylphenyl groups for ring-closing metathesis (RCM) leading to the synthesis of benzo-fused heterocycles was demonstrated by using a ruthenium-mediated isomerization followed by a ruthenium-mediated RCM reaction. This resulted in the syntheses of a variety of products including two substituted benzo[1,4]dioxins, a naphtho[2,3-b][1,4]dioxin, a 2H-chromene and a benzo[b]furan.     

Mass spectrometry of nitrogenous heterocycles. 1. Mass spectrometric evaluation of stability of tetrahydropyrazines annelated to five- and six-membered heterocycles

Based on a study of electron impact mass spectra of a large number of tetrahydropyrazines, which are joined to five- and six-membered heterocyclic and carbocyclic residues, the trends which characterize the stability of these condensed systems are found. The proposed criteria can be used for evaluation of the chemical stability of these compounds, for example, their propensity toward the reverse dissociation reaction.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 532–538, April, 1989.     

Reaction of anhydrides of dicarboxylic acids of six-membered nitrogen heterocycles with CH-acid compounds

Condensation products with azaphthalidylidene structures were obtained by the reaction of anhydrides of cinchomeronic and pyrazine-2,3-dicarboxylic acids with malonic ester, thiazolidine-2,4-dione, N-phenylthiazolidine-2,4-dione, and rhodanine. Azaindan-1,3-dione derivatives were synthesized with cyanoacetic ester and malononitrile under the same conditions. The reaction of these anhydrides, as well as quinolinic acid anhydride, with - and -methylquinolines, as well as 2,6-lutidine, gave compounds that have azaphthalidylidene structures, which were converted to azaquino- and pyrophthalones by the action of sodium methoxide.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1127–1131, August, 1981.     

Intramolecular hydrogen bonding with the participation of the nitrogen atom of five- and six-membered heterocycles

A comparison of the frequencies of the valence vibrations of the OH group and of the chemical shifts of the protons of the hydroxyl groups in -naphthol derivatives containing the nitrogen atom of the condensed ring of pyridine, pyrazine, 1,2,5-selenadiazole, 1,2,5-thiadiazole, 1,2,5-oxadiazole, and imidazole in the peri position to the hydroxyl group is indicative of the decisive effect of the molecular geometry on intramolecular hydrogen bonding in systems with rigidly fixed configurations. All conditions being equal, the intramolecular hydrogen bond is considerably weaker when the nitrogen atom is part of a five-membered rather than a six-membered heterocycle. This is explained not only by an increase in the distance between the proton donor and acceptor (which may be the same in some cases), but also by the greater deviation of the orbital of the unshared electron pair of the nitrogen of the five-membered heterocycle from the O...N line and, thus, by its greater distance from the hydrogen atom. For the same favorable molecular geometry, the OH...N bond is stronger than the OH...O bond because of the high basicity of the nitrogen atom.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 238–244, February, 1971.