Asymmetric transfer hydrogenation olefins and ketones catalyzed by metal complexes

Recent development in catalytic asymmetric transfer hydrogenation of olefins and ketones is reviewed. Unlike asymmetric hydrogenation using molecular hydrogen where chiral phosphine-transition metal complexes act as excellent catalysts, enantioselective transfer hydrogenation is effected with the aid of various well-designed nitrogen-based chiral ligands. 2-Propanol and an azeotropic mixture of formic acid and triethylamine can be used as stable organic hydrogen donors, The asymmetric reduction is viable as a practical tool for preparation of optically active compounds on a preparative scale.