Asymmetric Ruthenium-Catalyzed Transfer Hydrogenation of Ketones

Key words

ruthenium - transfer hydrogenation - tridentate N-ligands

Significance

Transition-metal-catalyzed asymmetric transfer hydrogenation (ATH) has become a leading reduction method, which can be credited to its broad scope and relatively mild conditions. Additionally, the development of more general methods to synthesize chiral secondary alcohol is a useful endeavor. Specifically, the ATH reduction of ortho-substituted aryl ketones is considered a more challenging transformation than that of related meta- and para-substituted substrates.

Comment

The authors report a ruthenium-catalyzed ATH of substituted aryl methyl ketones using a novel tridentate triazole containing ligand. The scope of this transformation is quite broad, and conversions and enantioselectivities range from moderate to excellent. Notably, tetralone and 4-chromanone can be reduced efficiently with synthetically useful enantioselectivity. The reduction of cyclohexyl methyl ketone proceeds with excellent conversion, yet enantioselectivity remains low (13% ee).