Search results for "Alkene"
showing 10 items of 98 documents
Geogenic and atmospheric sources for volatile organic compounds in fumarolic emissions from Mt. Etna and Vulcano Island (Sicily, Italy)
2012
[1] In this paper, fluid source(s) and processes controlling the chemical composition of volatile organic compounds (VOCs) in gas discharges from Mt. Etna and Vulcano Island (Sicily, Italy) were investigated. The main composition of the Etnean and Volcano gas emissions is produced by mixing, to various degrees, of magmatic and hydrothermal components. VOCs are dominated by alkanes, alkenes and aromatics, with minor, though significant, concentrations of O-, S- and Cl(F)-substituted compounds. The main mechanism for the production of alkanes is likely related to pyrolysis of organic-matter-bearing sediments that interact with the ascending magmatic fluids. Alkanes are then converted to alken…
l -Prolinoyl chiral picket iron porphyrins evaluated for the enantioselective epoxidation of alkenes
2003
International audience; Four atropisomers of an L-prolinoyl picket porphyrin were synthesised from tetra-o-aminophenyl porphyrin (TAPP) and were evaluated as alkene epoxidation catalysts after incorporation of iron in the porphyrin core. In the case of the aaaa atropisomer bearing the four amino groups on the same side, a bulky base was employed in order to suppress the eventual reaction on the non-functionalised side of the porphyrin.The resulting enantioselectivities were compared with either other chiral motifs or with the corresponding strapped porphyrins. The enantioselectivities obtained with picket porphyrins are as high as those for strapped porphryins, and in some cases, even highe…
A combined experimental and theoretical study of the thermal cycloaddition of aryl azides with activated alkenes.
2011
International audience; Reactions were performed from aryl azides on the one hand, and activated alkenes coming from β-dicarbonyl compounds or malonodinitrile on the other hand, either with recourse to conventional heating or to microwave activation, to afford 1-aryl-1H-1,2,3-triazoles. The mechanism and the regioselectivity of the reactions involving β-dicarbonyl compounds have been theoretically studied using DFT methods at the B3LYP/6-31G* level: they are domino processes comprising a tautomeric equilibrium of the β-dicarbonyl compounds with their enol forms, a 1,3-dipolar cycloaddition of the enol forms with the aryl azides (high activation energy), and a dehydration process (lower acti…
Electronic aspects of the hydride transfer mechanism. Ab initio analytical gradient studies of the cyclopropenyl‐cation/lithium hydride model reactan…
1985
The electronic mechanisms of a model hydride transfer reaction are theoretically studied with ab inito RHF and UHF SCF MO procedures at the 4‐31G basis set level and analytical gradient methods. The model system describes the reduction of cyclopropenyl cation to cyclopropene by the oxidation of lithium hydride to lithium cation. The molecular fragments corresponding to the asymptotic reactive channels characterizing the stepwise mechanisms currently discussed in the literature have been characterized. The binding energy between the fragments is estimated within a simple electrostatic approximate scheme. The results show that a hydride‐ion mechanism is a likely pathway for this particular sy…
Influence of nitric oxide on the generation and repair of oxidative DNA damage in mammalian cells
2002
We have analysed the effects of endogenously and exogenously generated nitric oxide (NO) in cultured mammalian fibroblasts on: (i) the steady-state (background) levels of oxidative DNA base modifications; (ii) the susceptibility of the cells to the induction of additional DNA damage and micronuclei by H(2)O(2); and (iii) the repair kinetics of various types of DNA modifications. Steady-state levels of oxidative DNA base modifications, measured by means of an alkaline elution assay in combination with the repair endonuclease Fpg protein, were similar in NO-overproducing B6 mouse fibroblasts stably transfected with an inducible NO synthase (iNOS) and in control cells. Increased oxidative dama…
Density functional theory study of the Lewis acid-catalyzed Diels-Alder reaction of nitroalkenes with vinyl ethers using aluminum derivatives
2002
The inverse electron demand Diels–Alder reaction of nitroalkenes with vinyl ethers catalyzed by Lewis acids based on aluminum metal, AlMe3, Al(OMe)3 and AlCl3 was studied using density functional theory methods. A continuum model was selected to represent the effects of dichloromethane used as solvent. For this cycloaddition reaction two reactive channels corresponding to the endo and exo approach modes of the vinyl ether to the Lewis acid-coordinated nitroalkene were studied. Coordination of the aluminum metal to an oxygen atom of the nitroalkene increases the electrophilicity of the heterodiene, decreasing the activation energy of the cycloaddition. The substitution effect on the aluminum…
A DFT study of the asymmetric (S)-5-(pyrrolidin-2-yl)-1H-tetrazole catalyzed Michael addition of carbonyl compounds to nitroalkenes
2007
Abstract The role of the ( S )-5-(pyrrolidin-2-yl)-1 H -tetrazole in the asymmetric organocatalyzed Michael addition of carbonyl compounds to nitroalkenes has been studied using DFT methods at the B3LYP/6-31G ∗∗ computational level. For the C–C bond-formation step, several reactive channels have been analyzed. The B3LYP/6-31G ∗∗ results, which are in reasonable agreement with the experiments, allow us to explain the stereoselectivity and the increase of the reactivity achieved by an intramolecular HB between the acid hydrogen of the tetrazole moiety and one oxygen atom of the nitroalkene.
Diversity-Oriented Synthesis of Highly Functionalized Alicycles across Dipolar Cycloaddition/Metathesis Reaction
2021
AbstractThis Account gives an insight into the selective functionalization of some readily available commercial cyclodienes across simple chemical transformations into functionalized small-molecular scaffolds. The syntheses involved selective cycloadditions, followed by ring-opening metathesis (ROM) of the resulting azetidin-2-one derivatives or isoxazoline frameworks and selective cross metathesis (CM) by discrimination of the C=C bonds on the alkenylated heterocycles. The CM protocols have been described when investigated under various conditions with the purpose on exploring chemodifferentiation of the olefin bonds and a study on the access of the corresponding functionalized β-lactam or…
Pauson-Khand reaction of internal dissymmetric trifluoromethyl alkynes. Influence of the alkene on the regioselectivity.
2014
Abstract: The scope of the Pauson-Khand reaction (PKR) of internal trifluoromethyl alkynes, previously described with norbornadiene, is expanded to norbornene and ethylene. A thorough structural analysis of the resulting PK adducts has been carried out to unveil that α-trifluoromethylcyclopentenones are preferred in all cases, independently of the electronic properties of the alkyne. The regioselectivity observed with norbornadiene and ethylene is higher than in the case of norbornene.