Probing the Importance of the Hemilabile Site of Bis(phosphine) Monoxide Ligands in the Copper-Catalyzed Addition of Diethylzinc to <i>N</i>-Phosphinoylimines: Discovery of New Effective Chiral Ligands

The hemilabile ligand Me-DuPHOS(O) 2 has proven to be a successful ligand for the copper-catalyzed addition of diethylzinc to N-phosphinoylimines. The corresponding α-chiral amines were obtained in high yields (80−98%) and enantiomeric ratios (19.0:1 to 99.0:1 er). Furthermore, this Cu•2 catalytic system has been shown to be effective in the addition of diethylzinc to nitroalkenes and in the reduction of β,β-disubstituted vinyl phenyl sulfones. This paper describes a general structure/selectivity study in which the three ligand subunits (chiral phospholane−linker−labile coordinating group (Z)) are systematically modified and tested in the copper-catalyzed addition of diethylzinc to the N-phosphinoylimine 1 derived from benzaldehyde. This study led to the discovery of a new class of effective chiral ligands that combine a chiral phospholane unit and an achiral phosphine oxide.