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[DOUBLE BOND]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 α,β-unsaturated esters and ketones, whereas analogous P,N ligands led to better results with dialkyl-phenyl-substituted alkenes and an allylic alcohol as substrates.