Chiral Proline-Based P,O and P,N Ligands for Iridium-Catalyzed Asymmetric Hydrogenation

Two new classes of proline-based P,O and P,N ligands were prepared and applied in the iridium-catalyzed asymmetric hydrogenation of alkenes. Both types of ligands induced high enantioselectivities in the hydrogenation of trisubstituted C?C bonds. Iridium complexes derived from P,O ligands bearing sterically demanding amide or urea groups at the pyrrolidine N-atom proved to be especially efficient catalysts for the conjugate reduction of alpha,beta-unsaturated esters and ketones, whereas analogous P,N ligands led to better results with dialkyl-phenyl-substituted alkenes and an allylic alcohol as substrates.