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Scientific article
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New chiral N-heterocyclic carbene ligands in palladium-catalyzed α-arylations of amides: conformational locking through allylic strain as a device for stereocontrol

Published inChemistry, vol. 16, no. 21, p. 6300-6309
Publication date2010
Abstract

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.

Keywords
  • Arylation
  • Asymmetric catalysis
  • Carbene ligands
  • N-heterocyclic carbenes
  • Oxindoles
  • Palladium
Citation (ISO format)
JIA, Yi-Xia et al. New chiral N-heterocyclic carbene ligands in palladium-catalyzed α-arylations of amides: conformational locking through allylic strain as a device for stereocontrol. In: Chemistry, 2010, vol. 16, n° 21, p. 6300–6309. doi: 10.1002/chem.201000031
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ISSN of the journal0947-6539
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