A Novel Class of P−O Monophosphite Ligands Derived from d-Mannitol:  Broad Applications in Highly Enantioselective Rh-Catalyzed Hydrogenations

We report on a new class of P−O monophosphite ligands (designated 3a−k) with a double six-membered-ring backbone onto which are attached additional groups and on applications of their Rh complexes in the hydrogenation of enamides, α-dehydroamino acid esters, dimethyl itaconate, and β-(acylamino)acrylates. Our results demonstrate that the Rh complexes with ligands 3a−k exhibit high enantioselectivity and reactivity in asymmetric hydrogenation reactions. An ee value of up to 98.0% was obtained for the hydrogenation of α-dehydroamino acid esters, and the ee values were all over 99% for the other three types of substrate, with a turnover number of up to 5000.