ENANTIOSELECTIVE ALLYLIC SUBSTITUTION CATALYZED BY CHIRAL [BIS(DIHYDROOXAZOLE)]PALLADIUM COMPLEXES - CATALYST STRUCTURE AND POSSIBLE MECHANISM OF ENANTIOSELECTION

P VONMATT, GC LLOYD-JONES, ABE MINIDIS, A PFALTZ, L MACKO, M NEUBURGER, M ZEHNDER, H RUEGGER, PS PREGOSIN, Guy Lloyd-Jones

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Abstract

Allylpalladium complexes with chiral bis(dihydrooxazole) ligands were studied as catalysts for the enantioselective allylic substitution reaction of rac-1,3-diphenylprop-2-enyl acetate (rac-5) with the anion of dimethyl malonate (Scheme 1). Using enantiomerically pure (S,E)-1-(4-tolyl)-3-phenylprop-2-enyl acatete ((S)-25) as substrate, the reaction was shown to proceed by a clean 'syn' displacement of acetate by dimethyl malonate (Scheme 6). The [Pd-II(eta(3)-allyl)] complex 18 and the analogous [Pd(eta(3)-1,3-diphenylallyl)] complex 20, both containing the same bis(dihydrooxazole) ligand, were characterized by X-ray structure analysis and by NMR spectroscopy in solution. The structural data reveal that steric interactions of the allyl system with the chiral ligand result in selective electronic activation of one of the allylic termini. The higher reactivity of one allylic terminus toward nucleophilic attack is reflected in a significantly longer Pd-C bond and a shift of the corresponding C-13-NMR resonance to higher frequency.

Original languageEnglish
Pages (from-to)265-284
Number of pages20
JournalHelvetica Chimica Acta
Volume78
Issue number2
Publication statusPublished - 1995

Keywords

  • CONTAINING OXAZOLINE LIGANDS
  • ASYMMETRIC-SYNTHESIS
  • (ETA-3-ALLYL)PALLADIUM COMPLEXES
  • SELECTIVE STABILIZATION
  • REPORTER LIGANDS
  • METAL-COMPLEXES
  • ALKYLATION
  • ALLYLATION
  • ACIDS
  • NMR

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