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

Abstract

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.

NCC Pincer Ni (II) Complexes Catalyzed Hydrophosphination of Nitroalkenes with Diphenylphosphine

“…On the basis of previous literatures, [ 17–21 ] a plausible mechanism was proposed (Scheme 3). Initially, replacement of chloride in Ni (II) complex 2a by OAc would afford Ni‐OAc complex I , which underwent transphosphination reaction with Ph 2 PH 4a to give Ni‐PPh 2 complex II .…”

“…[ 14–16 ] Specially, pincer complexes catalyzed hydrophosphination of electron‐deficient alkenes with secondary phosphines has been well established by the group of Duan, Leung, Pullarkat, Zhang, and Song groups. [ 17–21 ] Despite the above elegant work, most of the reported systems rely on precious palladium metal. It is thus highly desirable to develop earth‐abundant metal catalyzed hydrophosphination.…”

Recent Progress in Palladium-Catalyzed Asymmetric Hydrophos­phination

“…The asymmetric hydrophosphination of α,β,γ,δunsaturated ketones (Scheme 22) was subsequently reported. 40 This study was used to screen a library of PCP catalysts in order to understand the role of catalyst backbone design on enantioselectivity. Interestingly, changing the keto moiety in (R,R)-5 to a diester group (Scheme 22, catalyst (R,R)-6) can result in a dramatic increase in enantioselectivity (5% to 69%) under exactly the same (but unoptimized) conditions.…”

Efficient Synthesis of Malonate Functionalized Chiral Phosphapalladacycles and their Catalytic Evaluation in Asymmetric Hydrophosphination of Chalcone

“…The application of cyclopalladated complex ( R [N] )‐ 1 (Figure ) as catalysts in the synthesis of various chiral phosphine compounds via asymmetric hydrophosphination reactions of a variety of substrates including α,β‐ and α,β,γ,δ‐unsaturated malonate esters, α,β‐unsaturated carbonyl compounds, enones, and α,β‐unsaturated N ‐acylpyrroles has been highlighted recently. The CP compound ( R [P] )‐ 2 is known as an excellent catalyst for asymmetric P–H addition reaction of 4‐oxo‐enamides, N ‐enoyl phthalimides, benzoquinones.…”