Search results for "Alder"
showing 10 items of 273 documents
Quantitative Characterization of the Local Electrophilicity of Organic Molecules. Understanding the Regioselectivity on Diels−Alder Reactions
2002
Regional electrophilicity at the active sites of the reagents involved in polar Diels−Alder processes may be described on a quantitative basis using an extension of the global electrophilicity inde...
A Supramolecular Chiral Auxiliary Approach: “Remote Control ”of Stereochemistry at a Hierarchically Assembled Dimeric Helicate
2016
Dimeric hierarchically-assembled titanium(IV) helicates are in solvent-dependent equilibrium with the corresponding monomers. Statistically formed mixtures of such complexes bearing chiral stereocontrolling ligands and achiral diene-substituted ligands show high diastereoselectivity and reasonable enantioselectivity in the Diels-Alder reaction with maleimides if the reaction proceeds with the dimer but not with the monomer. Thus, solvent dependent switching between the monomer and dimer enables on/off switching of the enantioselectivity.
The linearized Calderón problem on complex manifolds
2019
International audience; In this note we show that on any compact subdomain of a Kähler manifold that admits sufficiently many global holomorphic functions , the products of harmonic functions form a complete set. This gives a positive answer to the linearized anisotropic Calderón problem on a class of complex manifolds that includes compact subdomains of Stein manifolds and sufficiently small subdomains of Kähler manifolds. Some of these manifolds do not admit limiting Carleman weights, and thus cannot by treated by standard methods for the Calderón problem in higher dimensions. The argument is based on constructing Morse holo-morphic functions with approximately prescribed critical points.…
ChemInform Abstract: New Structural Aspects of 3-Vinyl-1H-indoles for Predicting the Outcome of Diels-Alder Reactions
1989
Some selected 3-vinyl-1H-indoles have been synthesised and the first13C-NMR studies performed; in addition He(Iα) photoelectron spectra and the results of perturbation MO calculations of some examples of this class of compounds are presented. The molecular characteristics obtained thereby can be used to predict the results of [π4s+π2s]-cycloaddition reactions with 3-vinylindoles.
The tandem Diels-Alder reaction between acetylenedicarboxyaldehyde and N,N'-dipyrrolylmethane. An ab initio study of the molecular mechanisms
1998
Abstract An extensive exploration at RHF/3-21G and RHF/6-31G ∗ levels of the potential energy surface for the tandem cycloaddition of acetylenedicarboxyaldehyde to N,N'-dipyrrolylmethane allows us to characterize the reaction pathways and the associated stationary points. The formation of the pincer and/or domino adducts can be described as a stepwise mechanism. The first step, associated with an intermolecular [4 + 2] cycloaddition, is the rate determining step and an azanorbornadiene intermediate is obtained. The second step is an intramolecular [4 + 2] cycloaddition. The formation of the pincer adduct is the step which kinetically controls the global process, due to the low barrier heigh…
Toward an understanding of the unexpected regioselective hetero-Diels-Alder reactions of asymmetric tetrazines with electron-rich ethylenes: a DFT st…
2009
The regioselective hetero-Diels-Alder (HDA) reaction of asymmetric tetrazines (TTZs) with electron-rich (ER) ethylenes has been studied with use of DFT methods at the B3LYP/6-31G* level of theory. The reaction is a domino process that comprises three consecutive reactions: (i) a HDA reaction between the TTZ and the ER ethylene; (ii) a retro-Diels-Alder reaction with loss of nitrogen; and (iii) a beta-hydrogen elimination with formation of the final pyridazines. The first polar HDA reaction, which is associated to the nucleophilic attack of the ER ethylene to the electrophilically activated TTZ, is the rate and regioselectivity determining step of the domino process. The unexpected regiosele…
Invariance of electrophilicity of independent fragments. Application to intramolecular diels-alder reactions
2010
Abstract We herein demonstrate that the global electrophilicity may be distributed into fragments within a single molecule by using an empirical partitioning scheme of the electronic chemical potential framed on the chemical potential inequality principle. Group electrophilicity for several fragments may thereby be defined. Their values show a remarkable stability, independent of the chemical environment they are attached to. The model is applied to asses the chemical reactivity of a series of fragments involved in intramolecular Diels–Alder reactions.
Aplicación del binomio Apodemus sylvaticus /helminto como bioindicador de la regeneración del Parc Natural de la Serra Calderona (Comunitat Valencian…
2015
El estudio del binomio Apodemus sylvaticus/helminto ha sido propuesto como un bioindicador del proceso de regeneración postincendio en ecosistemas mediterráneos. El presente trabajo, enmarcado en un proyecto multidisciplinar que lleva por título “Procesos de Recuperación de Ecosistemas Perturbados por el Fuego a través del modelo Helmintos/Micromamíferos” y que fue iniciado por el grupo Parasites & Fire, del Departamento de Parasitología de la Universidad de Farmacia de la Universidad de Valencia, ofrece nuevos resultados que avalan su validación en el Parc Natural de la Serra Calderona (Comunitat Valenciana, España), la cual sufrió un devastador incendio forestal en 1992. Durante 21 años (…
Enclosure method for the p-Laplace equation
2014
We study the enclosure method for the p-Calder\'on problem, which is a nonlinear generalization of the inverse conductivity problem due to Calder\'on that involves the p-Laplace equation. The method allows one to reconstruct the convex hull of an inclusion in the nonlinear model by using exponentially growing solutions introduced by Wolff. We justify this method for the penetrable obstacle case, where the inclusion is modelled as a jump in the conductivity. The result is based on a monotonicity inequality and the properties of the Wolff solutions.