Sterically Hindered Chiral Ferrocenyl P,N,N-Ligands for Highly Diastereo-/Enantioselective Ir-Catalyzed Hydrogenation of α‑Alkyl-β-ketoesters via Dynamic Kinetic Resolution

A new
class of sterically hindered chiral ferrocenyl P,N,N-ligands have
been prepared through a two-step transformation from (Sc,Rp)-PPFNH2, in which a new (R)-stereogenic
center at the pyridinylmethyl position was generated in high diastereoselectivity.
With these newly developed P,N,N-ligands, Ir-catalyzed asymmetric
hydrogenation of various α-alkyl-substituted β-aryl-β-ketoesters
via dynamic kinetic resolution has been realized in high diastereo-
and enantioselectivities for the first time, which led to a variety
of optically active anti-β-hydroxyesters in
up to 99% ee. The study indicated that the additional stereocenter
at the pyridinylmethyl position of these ligands is crucial to realize
this hydrogenation.