Chiral Bicyclic Phosphoramidites-A New Class of Ligands for Asymmetric Catalysis

The development of new ligands for catalytic asymmetric C−C bond formation is of great interest to organic synthesis. We describe here a new class of chiral phosphoramidites that embody one or two binaphthol units attached to an achiral azabicyclic [3.3.1] or [3.3.0] framework. These ligands were easily accessible from (R)‐1,1′‐binaphthyl‐2,2′‐dioxaphosphorchloridite (4) and the corresponding heterobicyclic core 1, 2, or 3. They were employed in enantioselective Cu‐catalyzed additions of different dialkylzinc reagents to cyclic and acyclic enones. The chiral ketones were obtained with an enantiomeric ratio up to 91:9. The choice of the best ligand proved to be strongly dependent on each substrate. In addition, ligand 6 was found to be the most suitable for Rh‐catalyzed hydrogenations of α,β‐unsaturated esters, giving rise to dimethyl 2‐methylsuccinate and methyl N‐acetylalaninate with enantiomer ratios up to 95:5. An achiral bicyclic framework and one or two binaphthol units are components of a new class of chiral phosphoramidites (see examples shown). These ligands were successfully employed in enantioselective Cu‐catalyzed additions to enones and hydrogenations of α,β‐unsaturated esters.