Manganese-Catalyzed Asymmetric Transfer Hydrogenation of Aromatic Ketones With Chiral N6-Macrocyclic Ligands.

The manganese-catalyzed asymmetric transfer hydrogenation of ketones with chiral N6-macrocyclic ligands is reported. Employing 2-propanol as the hydrogen source, a broad range of chiral alcohols were obtained with excellent yields and enantioselectivities (up to 99% yield and 99% ee) under mild conditions with a catalyst loading of 1 mol %. Density functional theory calculations reveal that an isopropanol molecule participates in the transition states, and multiple noncovalent interactions among the macrocyclic ligand, the isopropanol molecule, and the ketone substrate exist, accounting for the unique macrocyclic effect and revealing the origin of product chirality. Moreover, an investigation of iridium-catalyzed asymmetric transfer hydrogenation using these chiral N6-macrocyclic ligands (2 mol %) demonstrates the superior performance of the manganese catalysts in comparison with their iridium counterparts.