The Experts below are selected from a list of 222 Experts worldwide ranked by ideXlab platform
Louis Barriault - One of the best experts on this subject based on the ideXlab platform.
-
origin of diastereoselectivity in the tandem oxy cope claisen ene reaction experimental and theoretical studies of the Ring Inversion mechanism
Journal of the American Chemical Society, 2007Co-Authors: Effiette L O Sauer, James Hooper, Louis BarriaultAbstract:We report herein a detailed investigation into the reaction mechanism of the oxy-Cope/Claisen/ene reaction. A series of chiral substrates was prepared, subjected to the tandem sequence, and the enantiomeric excess of the final products was evaluated. The observed conservation of enantiomeric excess was taken as evidence that the Ring Inversion of the intermediary enol ether does not occur. DFT calculations were used to map out the potential energy surface for the reaction and evaluate the relative energies of the Ring Inversions relative to those of the Claisen and ene reactions. Transition state energies thus obtained were found to support the presence of a high-energy transition state for the Ring Inversion of B to D provided R1 ≠ H. In addition, the calculations lent further support to the hypothesis that the selectivity of the transannular ene reaction is under Curtin−Hammett control.
-
Origin of Diastereoselectivity in the Tandem Oxy-Cope/Claisen/Ene Reaction: Experimental and Theoretical Studies of the Ring Inversion Mechanism
Journal of the American Chemical Society, 2007Co-Authors: Effiette L O Sauer, James Hooper, Louis BarriaultAbstract:We report herein a detailed investigation into the reaction mechanism of the oxy-Cope/Claisen/ene reaction. A series of chiral substrates was prepared, subjected to the tandem sequence, and the enantiomeric excess of the final products was evaluated. The observed conservation of enantiomeric excess was taken as evidence that the Ring Inversion of the intermediary enol ether does not occur. DFT calculations were used to map out the potential energy surface for the reaction and evaluate the relative energies of the Ring Inversions relative to those of the Claisen and ene reactions. Transition state energies thus obtained were found to support the presence of a high-energy transition state for the Ring Inversion of B to D provided R1 ≠ H. In addition, the calculations lent further support to the hypothesis that the selectivity of the transannular ene reaction is under Curtin−Hammett control.
Erich Kleinpeter - One of the best experts on this subject based on the ideXlab platform.
-
Dynamic 1H NMR Spectroscopic Study of the Ring Inversion in N-Sulfonyl Morpholines—Studies on N−S Interactions
Journal of Organic Chemistry, 2009Co-Authors: Ali Reza Modarresi-alam, Homeyra Alsadat Amirazizi, Hajar Bagheri, Hamid Reza Bijanzadeh, Erich KleinpeterAbstract:The effect of the exocyclic conjugation, via d−p orbital interaction and/or negative hyperconjugation (anomeric effect) of the N−S bond, on the Inversion of the morpholine Ring in some N-arylsulfonyl morpholines is studied by variable-temperature 1H NMR spectroscopy in different solvents. The observed free energy barriers are 9.2−10.3 kcal mol−1; the lower values were obtained with increasing conjugation (substituents of higher electron withdrawing power) along the series. The barrier to Ring Inversion of 1e was solvent independent. X-ray data of compounds 1b,d reveal the chair conformation of the six-membered Ring, the flattened pyramidal orientation of the Ring nitrogen atom, and the sulfonyl group in equatorial position with the plane containing the Caryl−S−N bond perpendicular to the plane of the benzene Ring. In addition, the sulfonamide group prefers a conformation with the S−C bond antiperiplanar with respect to the nitrogen atom lone pair and the −CH2−N−CH2− moieties in staggered conformation with...
-
dynamic 1h nmr spectroscopic study of the Ring Inversion in n sulfonyl morpholines studies on n s interactions
Journal of Organic Chemistry, 2009Co-Authors: Ali Reza Modarresialam, Homeyra Alsadat Amirazizi, Hajar Bagheri, Hamid Reza Bijanzadeh, Erich KleinpeterAbstract:The effect of the exocyclic conjugation, via d−p orbital interaction and/or negative hyperconjugation (anomeric effect) of the N−S bond, on the Inversion of the morpholine Ring in some N-arylsulfonyl morpholines is studied by variable-temperature 1H NMR spectroscopy in different solvents. The observed free energy barriers are 9.2−10.3 kcal mol−1; the lower values were obtained with increasing conjugation (substituents of higher electron withdrawing power) along the series. The barrier to Ring Inversion of 1e was solvent independent. X-ray data of compounds 1b,d reveal the chair conformation of the six-membered Ring, the flattened pyramidal orientation of the Ring nitrogen atom, and the sulfonyl group in equatorial position with the plane containing the Caryl−S−N bond perpendicular to the plane of the benzene Ring. In addition, the sulfonamide group prefers a conformation with the S−C bond antiperiplanar with respect to the nitrogen atom lone pair and the −CH2−N−CH2− moieties in staggered conformation with...
Effiette L O Sauer - One of the best experts on this subject based on the ideXlab platform.
-
origin of diastereoselectivity in the tandem oxy cope claisen ene reaction experimental and theoretical studies of the Ring Inversion mechanism
Journal of the American Chemical Society, 2007Co-Authors: Effiette L O Sauer, James Hooper, Louis BarriaultAbstract:We report herein a detailed investigation into the reaction mechanism of the oxy-Cope/Claisen/ene reaction. A series of chiral substrates was prepared, subjected to the tandem sequence, and the enantiomeric excess of the final products was evaluated. The observed conservation of enantiomeric excess was taken as evidence that the Ring Inversion of the intermediary enol ether does not occur. DFT calculations were used to map out the potential energy surface for the reaction and evaluate the relative energies of the Ring Inversions relative to those of the Claisen and ene reactions. Transition state energies thus obtained were found to support the presence of a high-energy transition state for the Ring Inversion of B to D provided R1 ≠ H. In addition, the calculations lent further support to the hypothesis that the selectivity of the transannular ene reaction is under Curtin−Hammett control.
-
Origin of Diastereoselectivity in the Tandem Oxy-Cope/Claisen/Ene Reaction: Experimental and Theoretical Studies of the Ring Inversion Mechanism
Journal of the American Chemical Society, 2007Co-Authors: Effiette L O Sauer, James Hooper, Louis BarriaultAbstract:We report herein a detailed investigation into the reaction mechanism of the oxy-Cope/Claisen/ene reaction. A series of chiral substrates was prepared, subjected to the tandem sequence, and the enantiomeric excess of the final products was evaluated. The observed conservation of enantiomeric excess was taken as evidence that the Ring Inversion of the intermediary enol ether does not occur. DFT calculations were used to map out the potential energy surface for the reaction and evaluate the relative energies of the Ring Inversions relative to those of the Claisen and ene reactions. Transition state energies thus obtained were found to support the presence of a high-energy transition state for the Ring Inversion of B to D provided R1 ≠ H. In addition, the calculations lent further support to the hypothesis that the selectivity of the transannular ene reaction is under Curtin−Hammett control.
Kenneth D M Harris - One of the best experts on this subject based on the ideXlab platform.
-
Ring Inversion of fluorocyclohexane in its solid thiourea inclusion compound
Magnetic Resonance in Chemistry, 1999Co-Authors: Robin K Harris, Alison Nordon, Kenneth D M HarrisAbstract:The rate of Ring Inversion of fluorocyclohexane in the solid inclusion compound that it forms with thiourea was studied using a variety of NMR techniques. Special use was made of F-19 NMR spectra acquired with high-power proton decoupling. Bandshape analysis was used in the range 237-300 K. The occurrence of Ring Inversion at lower temperatures was established by the two-dimensional EXSY method and the rates thereof were determined by selective polarization Inversion. Measurements of spin-lattice relaxation in the rotating frame showed a minimum at 300 K, yielding an additional value for the Ring Inversion rate. Variable-temperature triple-channel C-13-{H-1,F-19} spectra were studied. It is concluded that the average activation parameters (from the F-19 work) for the forward and backward Ring Inversion processes are Delta H double dagger=39.4+/-2.6 kJ mol(-1) and Delta S double dagger = - 12 +/- 11 J mol(-1) K-1. The near equality of the axial and equatorial populations makes accurate determination of separate barriers for the equatorial --> axial and axial --> equatorial processes problematic. The values are discussed in relation to those for other cyclohexane derivatives in their thiourea inclusion compounds and for fluorocyclohexane in other media. The superiority of the F-19 measurements over the use of C-13 spectra is emphasized.
-
Fluorocyclohexane Ring Inversion in a solid thiourea inclusion compound studied by fluorine-19 magic-angle spinning NMR with high-power proton decoupling
Chemical Communications, 1997Co-Authors: Alison Nordon, Robin K Harris, Kenneth D M HarrisAbstract:Variable-temperature 19 F magic-angle spinning NMR experiments involving high-power proton decoupling are used to examine the conformational preference and Ring-Inversion kinetics in the fluorocyclohexane–thiourea inclusion compound.
James Hooper - One of the best experts on this subject based on the ideXlab platform.
-
origin of diastereoselectivity in the tandem oxy cope claisen ene reaction experimental and theoretical studies of the Ring Inversion mechanism
Journal of the American Chemical Society, 2007Co-Authors: Effiette L O Sauer, James Hooper, Louis BarriaultAbstract:We report herein a detailed investigation into the reaction mechanism of the oxy-Cope/Claisen/ene reaction. A series of chiral substrates was prepared, subjected to the tandem sequence, and the enantiomeric excess of the final products was evaluated. The observed conservation of enantiomeric excess was taken as evidence that the Ring Inversion of the intermediary enol ether does not occur. DFT calculations were used to map out the potential energy surface for the reaction and evaluate the relative energies of the Ring Inversions relative to those of the Claisen and ene reactions. Transition state energies thus obtained were found to support the presence of a high-energy transition state for the Ring Inversion of B to D provided R1 ≠ H. In addition, the calculations lent further support to the hypothesis that the selectivity of the transannular ene reaction is under Curtin−Hammett control.
-
Origin of Diastereoselectivity in the Tandem Oxy-Cope/Claisen/Ene Reaction: Experimental and Theoretical Studies of the Ring Inversion Mechanism
Journal of the American Chemical Society, 2007Co-Authors: Effiette L O Sauer, James Hooper, Louis BarriaultAbstract:We report herein a detailed investigation into the reaction mechanism of the oxy-Cope/Claisen/ene reaction. A series of chiral substrates was prepared, subjected to the tandem sequence, and the enantiomeric excess of the final products was evaluated. The observed conservation of enantiomeric excess was taken as evidence that the Ring Inversion of the intermediary enol ether does not occur. DFT calculations were used to map out the potential energy surface for the reaction and evaluate the relative energies of the Ring Inversions relative to those of the Claisen and ene reactions. Transition state energies thus obtained were found to support the presence of a high-energy transition state for the Ring Inversion of B to D provided R1 ≠ H. In addition, the calculations lent further support to the hypothesis that the selectivity of the transannular ene reaction is under Curtin−Hammett control.
