Synthesis of a novel class of chiral N,N,N-tridentate pyridinebisimidazoline ligands and their application in Ru-catalyzed asymmetric epoxidations

A new class of easily tunable N,N,N-pyridinebisimidazoline (pybim) ligands have been synthesized. The synthesis and tunability of these chiral tridentate ligands are much easier and flexible compared to the popular pyboxes, making the former a suitable ligand tool box for various asymmetric transformations. Ruthenium complexes of the new ligands were synthesized and applied in the asymmetric epoxidation of olefins using hydrogen peroxide as the oxidant. Excellent yields and moderate to good enantioselectivities were achieved in the epoxidation of aromatic olefins. (c) 2005 Elsevier Ltd. All rights reserved.