Asymmetric Hydrogenation of α,β-Unsaturated Carboxylic Esters with Chiral Iridium N,P Ligand Complexes

Enantioselective conjugate reduction of a wide range of α,β-unsaturated carboxylic esters was achieved using chiral Ir N,P complexes as hydrogenation catalysts. Depending on the substitution pattern of the substrate, different ligands perform best. α,β-Unsaturated carboxylic esters substituted at the α position are less problematic substrates than originally anticipated and in some cases α-substituted substrates actually reacted with higher enantioselectivity than their β-substituted analogues. The resulting saturated esters with a stereogenic center in the α or β position were obtained in high enantiomeric purity.