Organopalladium intermediates in organic synthesis

5-aza-semicorrins: A new class of bidentate nitrogen ligands for enantioselective catalysis

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 [Pd11(η3-allyl)] complex 18 and the analogous [Pd(η3-1,3-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 PdC bond and a shift of the corresponding 13C-NMR resonance to higher frequency.

Enantioselective allylic substitution catalyzed by chiral [bis(dihydrooxazole)]palladium complexes - catalyst structure and possible mechanism of enantioselection

A. J. Wilkinson

Papers

314. Some observations on the preparation of π-allylic palladium chloride complexes