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Scarborough CC, Bergant A, Sazama GT, et al. Synthesis of Pd Complexes Bearing an Enantiomerically-Resolved Seven-Membered N-Heterocyclic Carbene Ligands and Initial Studies of their Use in Asymmetric Wacker-Type Oxidative Cyclization Reactions. Tetrahedron. 2009;65(26):5084-5092doi: 10.1016/j.tet.2009.04.072.
Scarborough, C. C., Bergant, A., Sazama, G. T., Guzei, I. A., Spencer, L. C., & Stahl, S. S. (2009). Synthesis of Pd Complexes Bearing an Enantiomerically-Resolved Seven-Membered N-Heterocyclic Carbene Ligands and Initial Studies of their Use in Asymmetric Wacker-Type Oxidative Cyclization Reactions. Tetrahedron, 65(26), 5084-5092. https://doi.org/10.1016/j.tet.2009.04.072
Scarborough, Christopher C, et al. "Synthesis of Pd Complexes Bearing an Enantiomerically-Resolved Seven-Membered N-Heterocyclic Carbene Ligands and Initial Studies of their Use in Asymmetric Wacker-Type Oxidative Cyclization Reactions." Tetrahedron vol. 65,26 (2009): 5084-5092. doi: https://doi.org/10.1016/j.tet.2009.04.072
Scarborough CC, Bergant A, Sazama GT, Guzei IA, Spencer LC, Stahl SS. Synthesis of Pd Complexes Bearing an Enantiomerically-Resolved Seven-Membered N-Heterocyclic Carbene Ligands and Initial Studies of their Use in Asymmetric Wacker-Type Oxidative Cyclization Reactions. Tetrahedron. 2009 Jun 27;65(26):5084-5092. doi: 10.1016/j.tet.2009.04.072. PMID: 20161255; PMCID: PMC2699314.
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Tetrahedron. 2009 Jun 27;65(26):5084-5092. doi: 10.1016/j.tet.2009.04.072.

Synthesis of Pd Complexes Bearing an Enantiomerically-Resolved Seven-Membered N-Heterocyclic Carbene Ligands and Initial Studies of their Use in Asymmetric Wacker-Type Oxidative Cyclization Reactions.

Tetrahedron

Christopher C Scarborough, Ana Bergant, Graham T Sazama, Ilia A Guzei, Lara C Spencer, Shannon S Stahl

Affiliations

  1. Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53706.

PMID: 20161255 PMCID: PMC2699314 DOI: 10.1016/j.tet.2009.04.072

Abstract

The development of enantiomerically-resolved, axially-chiral seven-membered N-heterocyclic carbene ((7)NHC) ligands for palladium is described. These (7)NHC ligands are derived from enatiomerically pure 2,2'-diamino-6,6'-dimethylbiphenyl, which is transformed via a synthetic sequence consisting of ortho-arylation, N-alkylation, and cyclization to afford seven-membered-ring amidinium salts. Synthesis of the 7-membered amidinium salts benefits from microwave irradiation, and in-situ metalation of the amidinium salts yields (7)NHC-Pd(II) complexes. The chiral (7)NHC-Pd complexes were examined as chiral catalysts under aerobic conditions in two intramolecular oxidative amination reactions of alkenes. In one case, enantioselectivities up to 63% e.e. were obtained, while the other substrate underwent cyclization to afford essentially racemic products. The catalytic data compare favorably to results obtained with a Pd(II) catalyst bearing a chiral five-membered-ring NHC ligand and, thereby, highlight the potential significance of this new class of chiral NHC ligands.

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