Preparation of pyrrolidine–oxazoline containing ligands and their application in asymmetric transfer hydrogenation

Nine members of a new ligand class incorporating both an oxazoline ring and a pyrrolidine unit were prepared in an efficient four-step synthesis starting from readily available chiral amino alcohols and proline. A study of these ligands in the asymmetric transfer hydrogenation of acetophenone showed that the catalysts formed from [Ir(cod)Cl]2 were the most active while those derived from [Ru(p-cymene)Cl2]2 gave the highest enantioselectivities (up to 61% ee).