Regio- and enantioselective allylic alkylation of an unsymmetrical substrate: A working model

The evolution of a model for understanding asymmetric allylic alkylations c atalyzed by palladium with the use of ligands derived from chiral diamines and 2-diphenylphosphinobenzoic acid provides a basis for attacking the prob lem of regio- and enantioselective alkylations proceeding through the inter mediacy of l-monosubstituted allyl complexes. The model predicted that in t he kinetic ionization of an achiral precursor the major enantiomer of the p roduct resulting from attack at the more substituted terminus would be the mirror image of that obtained under Curtin-Hammett conditions. Experimental ly, the ee was rationally varied from 66% of one enantiomer to 83% of the m irror image using the same ligand. Nonpolar solvents and the absence of cou nterions that coordinate to palladium favor the kinetic product. More polar solvents and counterions that coordinate well to palladium favor Curtin-Ha mmett conditions, For maximum regio- and enantioselectivity, the chiral rac emic 3-substituted-1-alkene is the preferred substrate.