Development of Chiral Spiro P-N-S Ligands for Iridium-Catalyzed Asymmetric Hydrogenation of -Alkyl--Ketoesters

The chiral tridentate spiro P-N-S ligands (SpiroSAP) were developed, and their iridium complexes were prepared. Introduction of a 1,3-dithiane moiety into the ligand resulted in a highly efficient chiral iridium catalyst for asymmetric hydrogenation of -alkyl--ketoesters, producing chiral -alkyl--hydroxyesters with excellent enantioselectivities (95-99.9% ee) and turnover numbers of up to 355000.