Asymmetric Transfer Hydrogenation of (Hetero)arylketones with Tethered Rh(III)-N-(p-Tolylsulfonyl)-1,2-diphenylethylene-1,2-diamine Complexes: Scope and Limitations.

A series of new tethered Rh(III)/Cp* complexes containing the N-(p-tolylsulfonyl)-1,2-diphenylethylene-1,2-diamine ligand have been prepared, characterized, and evaluated in the asymmetric transfer hydrogenation (ATH) of a wide range of (hetero)aryl ketones. The reaction was performed under mild conditions with the formic acid/triethylamine (5:2) system as the hydrogen source and provided enantiomerically enriched alcohols with good yields and high to excellent enantioselectivities. Although the nature of the substituents on the phenyl tethering ring did not alter the stereochemical outcome of the reaction, complexes bearing electron-donating groups exhibited a higher catalytic activity than those having electron-withdrawing groups. A scale-up of the ATH of 4-chromanone to the gram scale quantitatively delivered the reduced product with excellent enantioselectivity, demonstrating the potential usefulness of these new complexes.

Enantioselective Synthesis of α-Acetal-ß'-Amino Ketone Derivatives by Rhodium-Catalyzed Asymmetric Hydrogenation.

A range of ß-keto-γ-acetal enamides has been synthesized and transformed into the corresponding enantioenriched α-acetal-ß'-amino ketones with enantioinductions of up to 99% by using rhodium/QuinoxP*-catalyzed enantioselective hydrogenation under mild conditions. This method also proved to be highly chemoselective toward the reduction of the C-C double bond.