Synthesis of Tridentate PNO Ligands with Planar Chirality and Application in Iridium-Catalyzed Asymmetric Hydrogenation of Simple Ketones

A series of [2,2]paracyclophane-based tridentate PNO ligands with planar chirality were designed and synthesized. The easily prepared chiral tridentate PNO ligands were successfully applied to the iridium-catalyzed asymmetric hydrogenation of simple ketones, giving chiral alcohols with high efficiency and excellent enantioselectivities (up to 99% yield and >99% ee). Control experiments revealed the indispensability of both N-H and O-H in the ligands.