Asymmetric Synthesis. Asymmetric Catalytic Allylation Using Palladium Chiral Phosphine Complexes

Article abstract of DOI:10.1021/ja00293a038

The general characteristics of asymmetric catalytic allylation are analyzed in terms of the properties of the allyl acetate substrates and of the putative (?-allyl)palladium(II) intermediates.After examining the diastereometric equilibria of a series of ⁺ complexes, it was established that anti-disposed ?-allyl substituents are the major source of discrimination and that aryl substituents cause an enhancement of the epimerization rate and also are responsible for the greatest discrimination.The ?-allyl substituents appear to contribute additively to the discrimination, and a sector rule is proposed for predicting diastereomeric equilibrium constants.Under appropriate conditions, it is proposed that the optical yields of asymmetric catalytic allylation can be predicted from the chiral discrimination found for these ?-allyl intermediates.These proposals were tested and optical yields of up to 86percent are reported.Quantitative chemical yields were obtained, catalysis can be performed at 25 degC, and the products are readily transformed into useful chirons.The optical yields are sensitive to the chiral phosphine used but are insensitive to the nature of the nucleophiles that were used.There is an approximate correlation of the optical yield with the previously observed diastereomeric ratio of the corresponding (?-allyl)palladium intermediate.All of the reactions are completely regioselective, and all of the nucleophiles used gave the same prevailing enantiomer of the product for a given chiral phosphine.