Molecular Mechanics Predictions and Experimental Testing of Asymmetric Palladium-Catalyzed Allylation Reactions Using New Chiral Phenanthroline Ligands

Molecular mechanics calculations were used to probe the
conformational properties of a number of
substituted phenanthrolines and their η3-allylpalladium
complexes. Special attention was focused on
phenanthrolines
bearing chiral, terpene-derived, alkyl and alkenyl groups at C(2).
Based upon these calculations, predictions could
then be made regarding the suitability of the several ligands for use
in asymmetric palladium-catalyzed substitution
reactions of allylic acetates. Each of the substituted
phenanthrolines was prepared by straightforward means.
Use
of these ligands in catalytic allylations gave results which were in
good agreement with the calculation-based
predictions. The highest levels of asymmetric induction were
predicted and were obtained with a readily available
2-(2-bornyl)phenanthroline ligand 13. The results
were compared with previously reported data obtained using
other
ligands. Overall, this work provides further indication of the
potential utility of a combined calculational/experimental
approach for the design of chiral catalysts.