Development of Ion-Paired Chiral Ligands for Asymmetric Transition-Metal Catalysis

A new strategy for the design of a chiral ligand for asymmetric transition-metal catalysis has been developed. Our strategy is based on the development of achiral cationic ammonium-phosphine hybrid ligands paired with readily available chiral anions. These ion-paired chiral ligands impart a remarkable stereocontrolling ability to their palladium complexes, which catalyze highly enantioselective allylic alkylations of prochiral carbon nucleophiles. Moreover, the exploitation of ion-paired chiral ligands in combinatorial screening has enabled the rapid identification of the optimal ligand for the palladium-catalyzed new asymmetric allylation reaction. We also developed a highly enantio- and diastereoselective [3+2] annulation reaction of 5-vinyloxazolidinones and activated trisubstituted alkenes catalyzed by a palladium complex bearing a different type of ion-paired ligand, which allows for the single-step construction of three contiguous stereocenters, including vicinal all-carbon quaternary stereocenters.