Enantioselective Conjugate Addition of Dialkylzinc and Diphenylzinc to Enones Catalyzed by a Chiral Copper(I) Binaphthylthiophosphoramide or Binaphthylselenophosphoramide Ligand System

摘要

The enantioselective conjugate addition of dialkylzinc or diphe-nylzinc to enones was catalyzed by a copper(i)-axially chiral binaphthylthio-phosphoramide or binaphthylseleno-phosphoramide ligand system at room temperature (20 deg C) or 0 deg C,affording the Michael adducts in high yields with excellent ee for cyclic and acyclic enones.The enantioselectivity and reaction rate achieved here are one of the best results yet for the Cu-catalyzed conjugate addition to enones.It was revealed that this series of chiral phosphoramides was a novel type of S,N-bidentate ligands on the basis of ~(31)PNMR and ~(13)CNMR spectroscopic investigations.The mechanism of this asymmetric conjugate addition system has been investigated as well.We found that the acidic proton of phos-phoramide in these chiral ligands play a significant role in the formation of the active species.A bimetallic catalytic process has been proposed on the basis of previous literature.The linear effect of product ee and ligand ee further revealed that the active species is a monomeric Cu~I complex bearing a single ligand [Cu~I:ligand 1:1].