Synthesis and Application of Chiral Phosphorus Ligands Derived from TADDOL for the Asymmetric Conjugate Addition of Diethyl Zinc to Enones

Asymmetric conjugate addition of diethylzinc to cyclohexen-2-one, chalcone, and benzalacetone has been found to occur with 0.5% copper(II) triflate and 1% chiral phosphite. Cyclic phosphites derived from TADDOL gave excellent to moderate enantiomeric excesses. The nature of the exocyclic substituent of the dioxaphospholane ring is important, but the chiral induction is imposed by the TADDOL framework. Syntheses of all the TADDOL ligands are described.