Modular Synthesis of Chiral Trisubstituted 1,2-Allenyl Ketones Enabled by Organophosphine Dual-Reagent Catalysis

Despite significant progress in catalytic asymmetric synthesis of chiral allenes via homogeneous or heterogeneous metal-catalyzed, photoexcited metal-catalyzed as well as certain exquisite organocatalytic asymmetric methods, the asymmetric syntheses of chiral allenes via organo-phosphines catalysis are rare. In this paper, a catalytic asymmetric conjugate addition of malonic esters to yne-enones was successfully achieved via coperative catalysis of chiral biamide-phosphine and methyl acrylate, which afforded the corresponding chiral trisubstituted 1,2-allenyl ketones containing contigous axial and carbon center chirality with excellent enantioselectivity (up to 99% ee) and good diastereoselectivity (up to 93 : 7 dr). It is meaningful to note that the addition of an inorganic base (K₂CO₃) did not cause the background racemic reaction but could enhance the reactivity as a co-catalyst. The developed protocol demonstrates a wide range of substrates, high tolerance to various functional groups, versatile product functionalization and ease of operation as well as mild reaction conditions. Additionally, this coperative catalytic mode will not only promote the design of novel chiral phosphine catalysts, but also shine some light on expanding the reaction scope of asymmetric phosphine catalysis.