Further insight into the mechanism of Heck oxyarylation in the presence ofchiral ligands

Abstract

The Heck oxyarylation reaction to 3-benzyloxypterocarpan (15) has been studied in the presence of chiral phosphine ligands, a chiral ionic liquid and (+)-α.pinene. The observed small selectivities suggest that this reaction takes place through parallel pathways and the main pathway involves an achiral intermediate 11 where the chirality introduced by the chiral ligands is lost. Although practical asymmetric Heck oxyarylation to chiral pterocarpans could not be achieved, a convenient Heck-oxyarylation synthesis of rac-15 with (+)-α.pinene as ligand gave the highest yield reported to this type of reactions.