Iridium Catalysts With Modular Axial-Unfixed Biphenyl Phosphine-Oxazoline Ligands:Asymmetric Hydrogenation Of α-substituted Cinnamic Acid

In recent years,transition metal catalyzed asymmetric reaction has drawn much attention,which is one of the most atom-economic,green,efficient methods to access many critical chiral biologically active compounds and pharmaceuticals.What’s more,asymmetric hydrogenation is the standout among these effective reactions.And the design and synthesis of novel type of efficient chiral ligands is the key point of this research field.So far,thousands of ligands have been developed and proved useful in transition metal catalyzed asymmetric hydrogenation.However,the synthesis of ligands usually takes several difficult and expensive steps.Therefore,it is necessary to develop ligands of quickly,efficiently and cheaply composition,which can greatly promote the industrialization of asymmetric reaction.The specific research contents of this paper are as follows:(1)We have synthesized a series of new axis-unfixed biphenyl phosphine-oxzaoline ligands.The most significant feature of this kind of ligand is that they were originally a pair of diastereomers,when the catalyst with the iridium metal complex can only generate a single configuration.Thus,the ligand eliminates resolution step to avoid chemical waste.(2)These new type of chiral ligands were successfully applied to Ir-catalyzed asymmetric hydrogenation of a-substituted cinnamic acids and its derivatives,and the full conversions and the high enantioselectivities(up to 98%ee)were obtained.The results have shown that the new type of catalyst has extremely high activity and enantioselectivity.