A series of chiral spiroketal bisphosphine ligands containing 1,1'-spirobi(3 H,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.
Huang, J., Hong, M., Wang, C-C., Kramer, S., Lin, G-Q., & Sun, X-W. (2018). Asymmetric Synthesis of Chiral Spiroketal Bisphosphine Ligands and Their Application in Enantioselective Olefin Hydrogenation. Journal of organic chemistry, 83(20), 12838-12846. https://doi.org/10.1021/acs.joc.8b01693