Vinylic nucleophilic substitution in functionalized 2-vinylpyrroles: a route to a new family of stable enols

2-(2-Cyano-1-ethylthioethenyl)pyrroles easy exchange their ethylthio group for hydroxyl (NaOH, H₂O-methanol, 40-45 °C, 1 h) to give 2-(2-cyano-1-hydroxyethenyl)pyrroles, a new family of stable enols, in 50-94% yields. The vinylic nucleophilic substitution proceeds at the double bond of both the starting pyrroles and their cyclic isomers, 3-iminopyrrolizines. X-ray structure analysis and NMR spectra show the enols to be stabilized by exceptionally strong intramolecular H-bonding.     

Geometric isomerism in the series of fluoroalkyl-containing 1,2,3-trione 2-arylhydrazones

According to the ¹H, ¹³C, and ¹⁹F NMR data, fluoroalkyl-containing 1,2,3-trione 2-arylhydrazones in CDCl₃ exist exclusively, while in (CD₃)₂CO preferentially, as isomers in which the acyl or aroyl group is involved in intramolecular hydrogen bond. The isomer structure was assigned on the basis of the chemical shifts of the carbonyl carbon atoms and fluorine atoms and carbon-fluorine spin-spin coupling constants J _C-F. X-Ray diffraction data showed that 1,2,3-trione 2-arylhydrazones in crystal have the same structure as in CDCl₃ solution. Quantum-chemical calculations were performed to rationalize predominant formation of 1,2,3-trione 2-arylhydrazone isomers with a free polyfluoroacyl group.     

Tandem regio- and stereospecific cyclization of ethyl isonicotinate with cyanoacetylenic alcohols to provide novel polycondensed heterocyclic systems

Ethyl isonicotinate reacts with tertiary cyanoacetylenic alcohols under exceptionally mild conditions (room temperature, without catalyst or solvent) to afford novel polycondensed heterocyclic systems, 4,15-dioxa-7,12-diazapentacyclo[9.5.2.0^2,10.0^3,7.0^12,16]octadeca-8,17-dienes, in 30-68% yields. This tandem cyclization is regio- and stereospecific. Despite several asymmetric carbons (up to six) being present in the molecules, only one diastereomer is formed and both cyanomethylidene fragments possess exclusively Z-configuration. The tandem sequence includes the formation of 1,3-oxazolidino-1,2-dihydropyridines which undergo Diels-Alder cyclodimerization to give the final products.     

Unexpected diastereoselective one-pot assembly of hexahydroazulenones from 2-alkylcyclohexanones and arylacetylenes in KOH/DMSO suspension

2-Alkylcyclohexanones react with arylacetylenes (KOH/DMSO, 100 °C, 1 h) to afford unexpectedly hexahydroazulenones in 34-50% yields and ca. 100% diastereoselectivity (instead of the expected acetylenic alcohols), the minor products being isomeric arylethenyl ketones.     

Reactions of heterocumulenes with organometallic reagents: XVI. Quantum-chemical study on the mechanisms of formation of homo- and heteroannular azacycloheptadienes in reactions of 2-aza-1,3,5-trienes with potassium <Emphasis Type="Italic">tert</Emphasis>-butoxide

Mechanisms of intramolecular transformations of carbanions generated from 2-aza-1,3,5-trienes by the action of potassium tert-butoxide, which could lead to homo- or heteroannular azacycloheptadienes, were studied by quantum-chemical methods in terms of the density functional theory. The corresponding gradient channels were localized for model 1-methylsulfanyl-1-(cyclopentylideneamino)- and 1-methylsulfanyl-1-(cyclohexylideneamino)buta-1,3-dien-2-ols. Analysis of the kinetic and thermodynamic parameters showed that carbanion generated from N-cyclopentylidenebuta-1,3-dien-1-amine undergoes rearrangement mainly into homoannular azacycloheptadiene and that analogous N-cyclohexylidene derivative gives rise to heteroannular isomer. The results of calculations were consistent with the experimental data.     

Synthesis and structure of bis(2-phenylethyl) phosphine selenide

Bis(2-phenylethyl)phosphine selenide was obtained with 86% yield from bis(2-phenylethyl)phosphine and selenium. XRD, IR, UV, and multinuclear NMR spectroscopic studies revealed that the phosphorus atom in the bis(2-phenylethyl)phosphine selenide molecule is four-coordinated irrespective of the phase state (crystals or solution).     

Crystal and Molecular Structures of 3-Carboxypropyltriphenylphosphonium Diiodobromide

Complexation in the 3-carboxypropyltriphenylphosphonium bromide–molecular iodine system in chloroform was studied. The maximum number of iodine molecules coordinated by 3-carboxypropyltriphenylphosphonium bromide was established by the spectrophotometric method using a function of the average-iodine number, and the stability constant of the complex was determined. The [(C₆H₅)₃P(CH₂)₃COOH]BrI₂ diiodobromide was studied by X-ray diffraction analysis. The characteristic feature of the crystalline salt was the formation of dimer associates: anionic associates were formed due to the Br···Br intermolecular interactions and cationic associates were formed due to the O···H–O hydrogen bonds. The data obtained were correlated to the results of quantum-chemical calculations.     

New approach to the synthesis of azauracils and azaisocytosines

A new procedure was developed for the synthesis of 6-phenyltetrazolo[1,5-b]triazin-7-one. Aza analogs of uracil and isocytosine were prepared by the tetrazole ring cleavage. It was demonstrated that these transformations can be used in the synthesis of anomalous nucleosides. Dedicated to Academician O. M. Nefedov on the occasion of his 75th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1993–2001, November, 2006.     

Nitroalkyl-substituted tetrahydropyrazines in syntheses of azapolycyclic compounds

Tri-and tetracyclic compounds were synthesized by the cyclization of 6-alkoxy-2,3-dicyano-5-nitromethyl-1,4,5,6-tetrahydropyrazines with 1,2,3-triazinium and quinoxalinium cations. Dedicated to Academician A. L. Buchachenko on the occasion of his 70th birthday. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 2132–2137, September, 2005.