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A. B. F. Da Silva - One of the best experts on this subject based on the ideXlab platform.

  • Theoretical study on the stereochemistry of Intramolecular hetero Diels–Alder Cycloaddition reactions of azoalkenes
    International Journal of Quantum Chemistry, 2003
    Co-Authors: C.n Alves, Oscar A. S. Romero, A. B. F. Da Silva
    Abstract:

    The molecular mechanism for the Intramolecular hetero Diels–Alder Cycloaddition reactions of azoalkenes has been studied by using quantum mechanical calculations at the density functional theory (DFT) Becke's three-parameter exchange functional and the gradient-corrected functional of Lee, Yang, and Paar (B3LYP) and second-order Moller–Plesset (MP2) theory levels with the 6-31G* basis set. The molecular mechanism corresponds to a concerted mechanism with a slightly asynchronous bond-formation process where the formed internal bond (N4–C5) obtained with DFT is longer than the peripheral bond (C1–C6) formed in the transition state. Otherwise, the (C1–C6) bond obtained with MP2 is longer than the (N4–C5) bond formed in the transition state. Solvent (dichloromethane) effects have been considered with the polarizable continuum model (PCM). The MP2 calculations predicted an endo kinetic preference, whereas the DFT ones rendered endo/exo transition states that are practically isoenergetic. According to our analyses, the dispersion interaction (which stabilizes the endo orientation through π–π secondary contacts) and the solvent effects (which favor the exo addition) are the factors governing the stereoselectivity of the process. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 133–136, 2003

  • A theoretical study of the Intramolecular hetero Diels–Alder Cycloaddition reactions of azoalkenes
    Journal of Molecular Structure-theochem, 2001
    Co-Authors: C.n Alves, Oscar A. S. Romero, A. B. F. Da Silva
    Abstract:

    Abstract Ab initio Hartree–Fock and density functional theory calculations were performed to study transition geometries in Intramolecular Diels–Alder Cycloaddition reactions of azoalkene compounds. The Hartree–Fock (HF) calculations were formed at the RHF/3-21G level and the density functional theory (DFT) calculations were performed with the B3LYP functional and 6-31G ∗ basis set. The order of the reactivity of azoalkenes with different substituents in Intramolecular hetero Diels–Alder reactions was predicted from the frontier orbital energies, and calculations of the reaction barriers were performed. The HF and DFT calculations generated transition geometries with a very small degree of asynchronicity. The DFT results are in full agreement with experimental evidence and show the capability of this level of DFT calculation to predict the reactivity of Intramolecular hetero Diels–Alder Cycloaddition correctly.

C.n Alves - One of the best experts on this subject based on the ideXlab platform.

  • Theoretical study on the stereochemistry of Intramolecular hetero Diels–Alder Cycloaddition reactions of azoalkenes
    International Journal of Quantum Chemistry, 2003
    Co-Authors: C.n Alves, Oscar A. S. Romero, A. B. F. Da Silva
    Abstract:

    The molecular mechanism for the Intramolecular hetero Diels–Alder Cycloaddition reactions of azoalkenes has been studied by using quantum mechanical calculations at the density functional theory (DFT) Becke's three-parameter exchange functional and the gradient-corrected functional of Lee, Yang, and Paar (B3LYP) and second-order Moller–Plesset (MP2) theory levels with the 6-31G* basis set. The molecular mechanism corresponds to a concerted mechanism with a slightly asynchronous bond-formation process where the formed internal bond (N4–C5) obtained with DFT is longer than the peripheral bond (C1–C6) formed in the transition state. Otherwise, the (C1–C6) bond obtained with MP2 is longer than the (N4–C5) bond formed in the transition state. Solvent (dichloromethane) effects have been considered with the polarizable continuum model (PCM). The MP2 calculations predicted an endo kinetic preference, whereas the DFT ones rendered endo/exo transition states that are practically isoenergetic. According to our analyses, the dispersion interaction (which stabilizes the endo orientation through π–π secondary contacts) and the solvent effects (which favor the exo addition) are the factors governing the stereoselectivity of the process. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 133–136, 2003

  • A theoretical study of the Intramolecular hetero Diels–Alder Cycloaddition reactions of azoalkenes
    Journal of Molecular Structure-theochem, 2001
    Co-Authors: C.n Alves, Oscar A. S. Romero, A. B. F. Da Silva
    Abstract:

    Abstract Ab initio Hartree–Fock and density functional theory calculations were performed to study transition geometries in Intramolecular Diels–Alder Cycloaddition reactions of azoalkene compounds. The Hartree–Fock (HF) calculations were formed at the RHF/3-21G level and the density functional theory (DFT) calculations were performed with the B3LYP functional and 6-31G ∗ basis set. The order of the reactivity of azoalkenes with different substituents in Intramolecular hetero Diels–Alder reactions was predicted from the frontier orbital energies, and calculations of the reaction barriers were performed. The HF and DFT calculations generated transition geometries with a very small degree of asynchronicity. The DFT results are in full agreement with experimental evidence and show the capability of this level of DFT calculation to predict the reactivity of Intramolecular hetero Diels–Alder Cycloaddition correctly.

Oscar A. S. Romero - One of the best experts on this subject based on the ideXlab platform.

  • Theoretical study on the stereochemistry of Intramolecular hetero Diels–Alder Cycloaddition reactions of azoalkenes
    International Journal of Quantum Chemistry, 2003
    Co-Authors: C.n Alves, Oscar A. S. Romero, A. B. F. Da Silva
    Abstract:

    The molecular mechanism for the Intramolecular hetero Diels–Alder Cycloaddition reactions of azoalkenes has been studied by using quantum mechanical calculations at the density functional theory (DFT) Becke's three-parameter exchange functional and the gradient-corrected functional of Lee, Yang, and Paar (B3LYP) and second-order Moller–Plesset (MP2) theory levels with the 6-31G* basis set. The molecular mechanism corresponds to a concerted mechanism with a slightly asynchronous bond-formation process where the formed internal bond (N4–C5) obtained with DFT is longer than the peripheral bond (C1–C6) formed in the transition state. Otherwise, the (C1–C6) bond obtained with MP2 is longer than the (N4–C5) bond formed in the transition state. Solvent (dichloromethane) effects have been considered with the polarizable continuum model (PCM). The MP2 calculations predicted an endo kinetic preference, whereas the DFT ones rendered endo/exo transition states that are practically isoenergetic. According to our analyses, the dispersion interaction (which stabilizes the endo orientation through π–π secondary contacts) and the solvent effects (which favor the exo addition) are the factors governing the stereoselectivity of the process. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 95: 133–136, 2003

  • A theoretical study of the Intramolecular hetero Diels–Alder Cycloaddition reactions of azoalkenes
    Journal of Molecular Structure-theochem, 2001
    Co-Authors: C.n Alves, Oscar A. S. Romero, A. B. F. Da Silva
    Abstract:

    Abstract Ab initio Hartree–Fock and density functional theory calculations were performed to study transition geometries in Intramolecular Diels–Alder Cycloaddition reactions of azoalkene compounds. The Hartree–Fock (HF) calculations were formed at the RHF/3-21G level and the density functional theory (DFT) calculations were performed with the B3LYP functional and 6-31G ∗ basis set. The order of the reactivity of azoalkenes with different substituents in Intramolecular hetero Diels–Alder reactions was predicted from the frontier orbital energies, and calculations of the reaction barriers were performed. The HF and DFT calculations generated transition geometries with a very small degree of asynchronicity. The DFT results are in full agreement with experimental evidence and show the capability of this level of DFT calculation to predict the reactivity of Intramolecular hetero Diels–Alder Cycloaddition correctly.

Niru B. Soni - One of the best experts on this subject based on the ideXlab platform.

  • An Unusual Intramolecular Hetero-Diels−Alder Cycloaddition
    Journal of Organic Chemistry, 2005
    Co-Authors: Eric J. Stoner, Michael S. Allen, Alan C. Christesen, Rodger F. Henry, L. Steven Hollis, Robert F. Keyes, Ian Marsden, Tamara C. Rehm, Sandeep G. Shiroor, Niru B. Soni
    Abstract:

    A new reaction of erythronolides, an Intramolecular hetero-Diels−Alder, has been discovered. Heated aqueous alcoholic solutions of ABT-773 (1) and its cis isomer (3) convert slowly to cycloadducts 2 and 4, respectively. Optimal reaction conditions, mechanistic studies supported by molecular modeling, and biological activity data are reported. Single-crystal X-ray structures for both adducts 2 and 4 have been obtained.

Chihiro Kibayashi - One of the best experts on this subject based on the ideXlab platform.