Synthesis of novel chiral macrocyclic ONNO-type ligands and use in asymmetric transfer hydrogenation

Abstract

The interaction of 1,3-bis(2-formylphenoxy)-2-propanoI with chiral 1,2-diaminocyclohexane gave novel chiral macrocyclic ONNO-type ligands which were fully characterized by IR, NMR, MS and CD. The catalyst systems generated in situ from the chiral cyclic ONNO ligands and the iridium hydride complex [IrHCl2(COD)](2) have been used for the first time in the asymmetric transfer hydrogenation of aromatic ketones using 2-propanol as a source of hydrogen, giving the corresponding optically active alcohols with high chemical yields and good to excellent enantioselectivities (up to 92% ee). The reactions can be performed in air and the catalytic experiments are greatly simplified. (C) 2007 Elsevier B.V. All rights reserved.