P-Chiral Phosphine Ligands for Transition-Metal-Catalyzed Asymmetric Reactions

抄録

Optically active phosphine ligands possessing stereogenic centers on phosphorus atoms have been synthesized using phosphine-boranes as intermediates. Electron-rich P-chiral phosphine ligands (BisP, MiniPHOS, and DiSquareP) having a bulky alkyl group and a small alkyl group on the phosphorus atom exhibit excellent to almost perfect enantioselectivities in the Rh-catalyzed asymmetric hydrogenation of enamides and related substrates. Air-stable P-chiral phosphine ligands (t-Bu- and 1-Ad-QuinoxP) are also prepared with the phosphine-borane methodology. These ligands have exceedingly high enantioselectivities of up to 99.9% not only in Rh-catalyzed asymmetric hydrogenation but also in Rh- or Pd-catalyzed carbon-carbon bond-forming reactions.