Asymmetric Synthesis of Chiral Spiroketal Bisphosphine Ligands and Their Application in Enantioselective Olefin Hydrogenation

A series
of chiral spiroketal bisphosphine ligands containing 1,1′-spirobi­(3H,3′H)­isobenzofuran backbones was
accessed through asymmetric synthesis and subsequently tested in enantioselective
Rh-catalyzed hydrogenation of α-dehydroamino acid esters. The
ligand providing the highest enantioselectivity (up to 99.5%) was
obtained in seven steps in an overall 38% yield. The synthesis could
be performed on a gram scale, and no kinetic resolution of enantiomers
is required. Overall, the developed ligand provides an easily accessible
alternative to SDP ligands as well as other chiral bisphosphine ligands.