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Elucidating the mechanism of the asymmetric aza-Michael reaction

Academic Article
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Overview

authors

  • Phua, P. H.
  • Mathew, S. P.
  • White, A. J. P.
  • de Vries, J. G.
  • Blackmond, Donna
  • Hii, K. K.

publication date

  • 2007

journal

  • Chemistry-a European Journal  Journal

abstract

  • The mechanism of the palladium-catalysed asymmetric aza-Michael addition of aniline to alpha,beta-unsaturated N-imide was examined from several aspects using a combination of techniques, including X-ray crystallography, mass spectrometry, NMR, UV/Vis spectroscopy, and kinetic studies. The binding of aniline to the dicationic palladium(II) metal centre was found to occur in two consecutive steps: The binding of the first aniline is fast and reversible, whereas the binding of the second aniline is slower and irreversible. This occurs in competition with the binding of the N-imide, which forms a planar six-membered chelate ring with the metal centre; coordinating through the 1,3-dicarbonyl moiety. Isotopic labelling revealed that the addition of N-H occurs in a highly stereoselective manner, allowing the synthesis of optically active beta(2)- and beta(2,3)-amino acid derivatives. The stereochemistry of the addition is postulated to be syn. In situ kinetic studies provided evidence for product inhibition. The binding of the N-imide to the catalyst was found to be the rate-limiting step. Aniline was found to be an inhibitor of the pre-catalyst. The study culminated in the design of a new reaction protocol. By maintaining a low concentration of the aniline substrate during the course of the reaction, significant enhancement of yield and enantioselectivity can be achieved.

subject areas

  • Aniline Compounds
  • Aza Compounds
  • Catalysis
  • Crystallography, X-Ray
  • Imides
  • Kinetics
  • Ligands
  • Models, Molecular
  • Molecular Structure
  • Organometallic Compounds
  • Palladium
  • Stereoisomerism
  • Time Factors
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Research

keywords

  • Michael addition
  • asymmetric catalysis kinetics
  • palladium
  • reaction mechanism
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Identity

International Standard Serial Number (ISSN)

  • 0947-6539

Digital Object Identifier (DOI)

  • 10.1002/chem.200601706

PubMed ID

  • 17352437
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Additional Document Info

start page

  • 4602

end page

  • 4613

volume

  • 13

issue

  • 16

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