Use of the Trost Ligand in the Ruthenium‐Catalyzed Asymmetric Hydrogenation of Ketones

The Trost ligand, (1 S ,2 S )‐1,2‐diaminocyclohexane‐ N , N′ ‐bis(2′‐diphenylphosphinobenzoyl) ( L ), is reported for the first time as a ligand for the asymmetric hydrogenation (AH) of ketones. Ligand ( S , S )‐ L was screened in the presence of several metal salts and was found to form active catalysts if combined with ruthenium sources in the presence of hydrogen and a base. Reaction optimization was performed by screening different Ru sources, solvents, and bases. Under the optimized conditions, the complex formed by the combination of ( S , S )‐ L with RuCl 3 (H 2 O) x in the presence of Na 2 CO 3 was able to promote the AH of several ketones at room temperature in good yields with up to 96 %  ee . The reaction kinetics measured under the optimized conditions revealed the presence of a long induction period, during which the initially formed Ru species was transformed into the catalytically active complex by reaction with hydrogen. Remarkably, a ketone that is a precursor of the antiemetic drug aprepitant was hydrogenated in excellent yield with a good ee value.