9,10-syn-podocarpane diterpenoids. An approach to the tricyclic skeleton by Diels-Alder cycloaddition: related crystal structure determination and theoretical aspects
TL;DR: In this article, a tricyclique de structure voisine de celle des precurseurs des podocarpanes, par cycloaddition du vinylcyclohexene avec l'acide benzoquinone-1,4 carboxylique, is presented.
Abstract: On prepare un compose tricyclique de structure voisine de celle des precurseurs des podocarpanes, par cycloaddition du vinylcyclohexene avec l'acide benzoquinone-1,4 carboxylique. On etudie la structure cristalline du compose et on explique par une etude theorique la stereochimie de la reaction
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TL;DR: Intermolecular perturbation theory has been used to treat the regioselectivity observed with [4+2] cycloadditions to quinones using 15 model reactions which are key steps in the synthesis of a number of biologically important natural as well as synthetic products as discussed by the authors.
Abstract: Intermolecular perturbation theory has been used to treat the regioselectivity observed with [4+2] cycloadditions to quinones Using 15 model reactions which are key steps in the synthesis of a number of biologically important natural as well as synthetic products the usefulness of this theoretical method for predicting the regioselectivity of cycloadditions is clearly demonstrated Furthermore the various contributions to the total interaction energy are discussed in some detail
6 citations
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TL;DR: Masked o-benzoquinones (MOBs) were generated in situ from 2-methoxyphenols, underwent Diels-Alder reactions with 1-vinylcyclohexenes to produce the corresponding cycloaddition products, that is, decahydrophenanthrenes along with bicyclo[2.2]octenones.
5 citations
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TL;DR: In this article, a model which makes use of the complete perturbation treatment of Salem and Devaquet has been applied to Diels-Alder reactions and is now proposed for the interpretation of regioselectivity in the 1,3-dipolar cycloadditions of 3,5-dichloro-2,4,6-trimethylbenzonitrile oxide with some hetero-aromatic systems.
Abstract: A model which makes use of the complete perturbation treatment of Salem and Devaquet has already been applied to Diels–Alder reactions and is now proposed for the interpretation of regioselectivity in the 1,3-dipolar cycloadditions of 3,5-dichloro-2,4,6-trimethylbenzonitrile oxide with some heteroaromatic systems. The van der Waals minima relevant to the hypothesized alternative reaction paths have been suggested as model structures (perturbed states) for the corresponding weakly interacting complexes in the early stages of the reaction. To evaluate the atom–atom non-bonded interactions between polar partners an explicit Coulombic term is added to the Lennard-Jones (6–12) function previously used. Moreover, because of the dominant contribution of non-interacting atoms in determining the van der Waals minima, the minimization procedure is constrained to the region of the non-bonding energy hypersurface where the 2pπ-orbitals involved in the new bond formation overlap significantly. The obtained regioselectivities are in good agreement with experimental ones.
5 citations
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TL;DR: In this article, a model which makes use of the complete perturbative treatment of Salem and Devaquet is proposed for the interpretation of regio-, sito- and stereo-selectivity of cycloaddition reactions.
Abstract: A model which makes use of the complete perturbative treatment of Salem and Devaquet is proposed for the interpretation of regio-, sito- and stereo-selectivity of cycloaddition reactions. The van der Waals intermolecular interaction potential-energy surface minima relevant to the hypothesized alternative reaction paths are suggested as model structures (perturbed states) for the corresponding weakly interacting complexes in the early stages of the reaction. It is shown how results are affected by the increase in the degrees of freedom for the approach of the two interacting molecules, by the choice of a particular atom-atom potential and by the two-partner internal-geometry relaxation which occurs at the perturbed state. The results obtained for some sample reactions (butadiene and ethylene, penta-1,3-diene and acrolein, penta-1,3 -diene and 2,5-dimethyl-1,4-benzoquinone) corroborate our previous choice of a Lennard-Jones function and of an undistorted reagent geometry to localize the non-bonding minima. The inclusion of a greater number of intermolecular variables and their simultaneous optimization during the non-bonding minima localization is a marked improvement for the definition of the perturbed state. The results obtained for the reactions of mono- and di-substituted dienes with unsymmetrically substituted quinones confirm the predictive ability of our improved procedure.
4 citations
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TL;DR: This comprehensive study portrays that p-toluenesulfonic acid is a more efficient catalyst for the reaction between p-quinones and 3,4-dihydro-2H-pyran, than the Lewis acids.
Abstract: This comprehensive study portrays that p-toluenesulfonic acid is a more efficient catalyst for the reaction between p-quinones and 3,4-dihydro-2H-pyran, than the Lewis acids. The products were accomplished by the Diels–Alder cycloaddition reaction and their mechanistic pathways have been formulated. The impact of C2 and C2,5 substituents of the p-quinones on the cycloaddition reaction has been explored. Remarkably, it is the first report to explore this kind of in situ generated diene for the Diels–Alder cycloaddition reaction.
4 citations
References
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TL;DR: In this article, the synthesis of (±)-4,4-dinor-9βH-pimara-7,15-diene, 4, a model compound for momilactones, has been achieved via stereospecific Diels-Alder reaction and alkylation.
9 citations
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TL;DR: Intermolecular perturbation theory has been used to treat the regioselectivity observed with [4+2] cycloadditions to quinones using 15 model reactions which are key steps in the synthesis of a number of biologically important natural as well as synthetic products as discussed by the authors.
Abstract: Intermolecular perturbation theory has been used to treat the regioselectivity observed with [4+2] cycloadditions to quinones Using 15 model reactions which are key steps in the synthesis of a number of biologically important natural as well as synthetic products the usefulness of this theoretical method for predicting the regioselectivity of cycloadditions is clearly demonstrated Furthermore the various contributions to the total interaction energy are discussed in some detail
6 citations
••
TL;DR: Masked o-benzoquinones (MOBs) were generated in situ from 2-methoxyphenols, underwent Diels-Alder reactions with 1-vinylcyclohexenes to produce the corresponding cycloaddition products, that is, decahydrophenanthrenes along with bicyclo[2.2]octenones.
5 citations
••
TL;DR: In this article, a model which makes use of the complete perturbation treatment of Salem and Devaquet has been applied to Diels-Alder reactions and is now proposed for the interpretation of regioselectivity in the 1,3-dipolar cycloadditions of 3,5-dichloro-2,4,6-trimethylbenzonitrile oxide with some hetero-aromatic systems.
Abstract: A model which makes use of the complete perturbation treatment of Salem and Devaquet has already been applied to Diels–Alder reactions and is now proposed for the interpretation of regioselectivity in the 1,3-dipolar cycloadditions of 3,5-dichloro-2,4,6-trimethylbenzonitrile oxide with some heteroaromatic systems. The van der Waals minima relevant to the hypothesized alternative reaction paths have been suggested as model structures (perturbed states) for the corresponding weakly interacting complexes in the early stages of the reaction. To evaluate the atom–atom non-bonded interactions between polar partners an explicit Coulombic term is added to the Lennard-Jones (6–12) function previously used. Moreover, because of the dominant contribution of non-interacting atoms in determining the van der Waals minima, the minimization procedure is constrained to the region of the non-bonding energy hypersurface where the 2pπ-orbitals involved in the new bond formation overlap significantly. The obtained regioselectivities are in good agreement with experimental ones.
5 citations
••
TL;DR: In this article, a model which makes use of the complete perturbative treatment of Salem and Devaquet is proposed for the interpretation of regio-, sito- and stereo-selectivity of cycloaddition reactions.
Abstract: A model which makes use of the complete perturbative treatment of Salem and Devaquet is proposed for the interpretation of regio-, sito- and stereo-selectivity of cycloaddition reactions. The van der Waals intermolecular interaction potential-energy surface minima relevant to the hypothesized alternative reaction paths are suggested as model structures (perturbed states) for the corresponding weakly interacting complexes in the early stages of the reaction. It is shown how results are affected by the increase in the degrees of freedom for the approach of the two interacting molecules, by the choice of a particular atom-atom potential and by the two-partner internal-geometry relaxation which occurs at the perturbed state. The results obtained for some sample reactions (butadiene and ethylene, penta-1,3-diene and acrolein, penta-1,3 -diene and 2,5-dimethyl-1,4-benzoquinone) corroborate our previous choice of a Lennard-Jones function and of an undistorted reagent geometry to localize the non-bonding minima. The inclusion of a greater number of intermolecular variables and their simultaneous optimization during the non-bonding minima localization is a marked improvement for the definition of the perturbed state. The results obtained for the reactions of mono- and di-substituted dienes with unsymmetrically substituted quinones confirm the predictive ability of our improved procedure.
4 citations