Chiral pyridyl phosphinites with large aryl substituents as efficient ligands for the asymmetric iridium-catalyzed hydrogenation of difficult substrates

Using a flexible synthesis, new chiral iridium N,P complexes with sterically demanding aryl substituents were synthesized and used in the asymmetric hydrogenation of difficult substrates. Unprecedented enantioselectivities were obtained in the asymmetric hydrogenation of α-substituted α,β-unsaturated esters and dihydronaphthalenes. The variety of aryl substituents incorporated into the catalyst has made it possible to obtain useful structure selectivity relationships for important classes of substrates.