Kinetic Resolution of Planar-Chiral Ferrocenylphosphine Derivatives by Molybdenum-Catalyzed Asymmetric Ring-Closing Metathesis and Their Application in Asymmetric Catalysis

Highly enantioselective kinetic resolution of racemic planar-chiral metallocenylphosphine sulfides was realized by the molybdenum-catalyzed asymmetric ring-closing metathesis reaction with the k_rel values of up to 147. The enantiomerically enriched 1,4-but-2-enylene-bridged ferrocenylphosphine sulfides thus obtained could be purified to enantiomerically pure forms by simple recrystallization from hot methanol, and subsequent reduction of the phosphine sulfides provided the corresponding planar-chiral phosphines with retention of the enantiomeric homogeneity. This is a rare example of preparing planar-chiral ferrocenylphosphines by catalytic asymmetric reactions. The single-enantiomer planar-chiral ferrocenylphosphines were applied as chiral ligands in the rhodium-catalyzed asymmetric 1,4-addition reaction (the Hayashi–Miyaura conjugate addition reaction) of phenylboronic acid to 2-cyclohexenone to show excellent enantioselectivity and high yields. The NMR studies clarified that the butenylene-bridged ferrocenylphosphine coordinated to a rhodium­(I) cation in a monodentate fashion and an interaction of the bridging olefin moiety to the rhodium atom was not detected.