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[en] Review shows the new strategies in the synthesis of heterocycles, having nitrogen, oxygen and sulfur atoms, via transition metals catalyzed intramolecular cyclization of acetylenic compounds on the data published at the last 30 years, Unsaturated heterocyclic compounds (pyrroles and pyrroline, furans, dihydro furans and benzofurans, indoles and iso-indoles, isoquinolines and isoquinolinones, aurones, iso coumarins and oxazolinone, lactams and lactones with various substitutes in heterocycles) are formed by transition metals, those salts [PdCl2, Pd(OAc)2, HgCl2, Hg(OAc)2, Hg(OCOCF3)2, AuCl3·2H2O, NaAuCl4·2H2O, CuI, CuCl], oxides (HgO) and complexes [Pd(OAc)2(PPh3)2, Pd(PPh3)4, PdCl2(MeCN)2, Pd(OAc )2/TPPTS] catalyzed intramolecular cyclization of acetylenic amines, amides, ethers, alcohols, acids, ketones and βdiketones. More complex hetero polycyclic systems typical for natural alkaloids can to obtain similar. Proposed mechanisms of pyrroles, isoquinolines, iso indoles and indoles, benzofurans and iso coumarins, thiazolopyrimidinones formation are considered. (author)
[en] The review covers methods for the synthesis of aza(deaza)xanthines, i.e., fused pyrrolo-, pyrazolo- and triazolopyrimidine heterocyclic systems, which are common core structures of various biologically active compounds. The extensive range of modern synthetic approaches is organized according to target structures and starting building blocks. The presented material is intended to benefit broad audience of specialists in the fields of organic, medicinal and pharmaceutical chemistry. The bibliography includes 195 references
[en] Data on key chemical transformations of thiosemicarbazides resulting in heterocyclic compounds are generalized and described systematically. Methods for the synthesis of five- and six-membered heterocycles with two and three heteroatoms are considered. The bibliography includes 190 references.
[en] The published data on the methods of synthesis and chemical transformations of nitrogenous heterocyclic compounds spiro-fused with a cyclopropane fragment are described systematically and generalised. The bibliography includes 146 references.
[en] Full text. Experimental studies of electron collisions with furan, pyrrole, thiophene and their corresponding aza-derivatives show the occurrence of several resonant states at low impact energies (0-10 eV), for all the structures. These resonances are associated with the occupation of an unoccupied molecular orbital by the incident electron, and the consequent formation of a temporary anionic state, or resonance. Theoretical studies of elastic electron collisions with furan and pyrrole also show the presence of shape resonances in good agreement with the experimental positions of the resonance peaks. In this work we present integral cross sections for elastic scattering of low-energy electrons by the aza-derivatives of furan, pyrrole and thiophene, namely, oxazole, isoxazole, imidazole, pyrazole, thiazole and isothiazole. Our studied structures differ from furan, pyrrole and thiophene by the substitution of a C-H by an N atom, in different positions of the ring. The ground state geometry was optimized using second order perturbation theory with the TZV++(2d,1p) basis set. The molecular ground state was described in the Hartree-Fock approximation, and the virtual molecular orbitals obtained were used to represent the scattering orbitals. In order to compute the elastic cross sections we employed the Schwinger multichannel method implemented with pseudopotentials of Bachelet, Hamann and Schlueter, in the static-exchange approximation. The six molecules present shape resonances at low energies, in both A' and A'' symmetries. Electronic structure calculations were performed in order to characterize the resonant orbitals. Each of the three pairs of isomers presented very similar integral cross sections at high energies. At low energies, on the other hand, the cross sections become more distinct, specially due to the different positions of the resonances. We also discuss the effects on the cross sections caused by aza-substitution, when compared to the results of furan and pyrrole. For a better description of the scattering process, the polarization of the molecular target by the incident electron must be taken into account, which will be done in a second step. This way, we would be able to compare the computed positions of the resonances with the experimental values
[en] Syntheses of modified steroids annulated at the 16-, 17-positions with five- and six-membered heterocycles are reviewed. The biological activity profiles of these compounds as important secondary metabolites are described.
[en] The data on the reactivity of sulfur monochloride published in the past 15 years have been reviewed and systematized. The review focuses on the synthesis of acyclic and heterocyclic compounds with the use of S_2Cl_2. The bibliography includes 154 references
[en] Highlights: • The aerogen–π bonds involving π systems have been studied. • The configuration of complex has a significant effect on its stability. • The aerogen–π interaction attributes its stability to approximately equal parts electrostatic and polarization energies. Ab initio calculations have been performed to study the complexes of XeOF2 and a series of π systems including ethyne, ethene, benzene, pyrrole, furan, and thiophene. More than two structures were obtained for each complex with an aerogen–π bond. The configuration of complex has a significant effect on its stability. The strength of aerogen–π interaction is comparable with that of lone pair–aerogen interaction and conventional hydrogen bonds. A breakdown of the aerogen–π interaction attributes its stability to approximately equal parts electrostatic and polarization energies, with a relatively smaller contribution from dispersion energy.
[en] The photochemistry of cyclobutanes and saturated four-membered heterocycles with two exocyclic double bonds (except bisalkylidenecyclobutanes) is reviewed. Emphasis is laid on photoproducts rather than on mechanism, with special regard for the formation of (hetero)methylenecyclopropanes via photoextrusion of small stable molecules. (author)