Asymmetric 1,4-Conjugate Addition of Diarylphosphines to α,β,γ,δ-Unsaturated Ketones Catalyzed by Transition-Metal Pincer Complexes

An
enantioselective asymmetric 1,4-addition of diarylphosphines
to linear α,β,γ,δ-unsaturated dienones was
developed. A series of chiral PCP- and PCN-transition-metal (Pd, Pt
and Ni) pincers, themselves prepared catalytically via asymmetric
hydrophosphination, were sequentially screened to reveal the roles
of backbone architecture and metal ion in catalyst design. The selected
ester-functionalized PCP-palladium pincer afforded the chiral 1,4-phosphine
adducts in excellent yields with up to >99% ee. The
same catalyst when utilized for the hydrophosphination of an α,β,γ,δ-unsaturated
malonate ester also revealed the critical role played by the ester
functionality on the ligand backbone in dictating the enantioselectivity
of the 1,6-adduct.