Ruthenium(II)‐Catalyzed Asymmetric Transfer Hydrogenation of Carbonyl Compounds with 2‐Propanol and Ephedrine‐Type Ligands

Abstract This account describes the development and application of Noyori's type catalysts based on ruthenium‐arene complexes and simple chiral β‐amino alcohols derived from ephedrine, for the asymmetric transfer hydrogenation of 2‐propanol to carbonyl substrates. The influence of key parameters of the catalyst system has been studied systematically, resulting in particular in the design of the novel ligand (4‐biphenylmethyl)norephedrine. Thanks to the latter, the catalytic precursors and true active species could be isolated for the first time, enabling a complete structural description of the catalytic cycle and of probable deactivation pathways. Highly effective applications of those catalysts systems, i.e., the asymmetric reductions of simple aryl ketones and aryl β‐keto esters, the synthesis of chiral phthalides and syn ‐β ,δ ‐dihydroxy esters, are described.