Synthesis of Chiral Olefin Ligands and their Application in Asymmetric Catalysis

Chiral olefins have recently emerged as among the most promising ligands for asymmetric catalysis. In the past nearly ten years, significant advances have been made in developing ligands, including diene and heteroatom/olefin hybrid ligands, and exploring their applications in challenging metal-catalyzed asymmetric reactions. Especially in some cases, chiral olefin ligands have an obvious advantage over some conventional chiral ligands in terms of activity and selectivity. Besides the most often studied rigidly bicyclic dienes, readily accessible chiral-chain dienes with flexible frameworks and two terminal olefins as coordinating groups have also proven to be effective for achieving high levels of enantioselectivity in transition-metal-catalyzed asymmetric reactions. Moreover, the terminal olefins can be combined with phosphorus atoms on suitable chiral skeletons for the development of novel phosphorus/olefin (P/olefin) hybrid ligands, which have high activity and selectivity in Pd-catalyzed asymmetric transformations. Significantly, sulfur/olefin (S/olefin) hybrid ligands have been successfully explored and applied in a range of Rh-catalyzed asymmetric transformations. This Focus Review will mainly discuss the synthesis of recently developed chiral-chain diene ligands, phosphorus/terminal-olefin hybrid ligands, and sulfur/olefin hybrid ligands, and their application in asymmetric catalysis.