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Publication 149  


  1. “New Chiral N-Heterocyclic Carbene Ligands in Palladium-Catalyzed α-Arylations of Amides: Conformational Locking through Allylic Strain as a Device for Stereocontrol”
    Y.-X. Jia, D. Katayev, G. Bernardinelli, T.M. Seidel, E.P. Kündig,
    Chem. Eur. J. 2010, 16, 6300-6309.

New Enders/Herrmann-type chiral N-heterocyclic carbene (NHC) ligands have been developed and applied in asymmetric palladium-catalyzed intramolecular α-arylations of amides. The best ligands feature the bulky tert-butyl group and ortho-substituted aryl groups at the stereogenic centers. Aryl bromides readily react at room temperature and aryl chlorides at 50 °C. The highly enantiomerically enriched (up to 96 % ee) 3-alkyl-3-aryloxindole products were obtained in generally high yields (>95 %) except in cases of steric congestion. The critical roles both of the bulky alkyl group and of the ortho-aryl substituent at the stereogenic center of the ligand were revealed in the crystal structure of a [Pd(η3-allyl)(NHC-L*)(I)] complex. The ligand aryl location and orientation is fixed by conformational locking that minimizes A1,3-strain and enables optimal transfer of chiral information.

DOI : 10.1002/chem.201000031 

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