Asymmetric Binary-Acid Catalysis with Chiral Phosphoric Acid and MgF2: Catalytic Enantioselective Friedel-Crafts Reactions of β,γ-Unsaturated α-Ketoesters

A unique binary chiral phosphoric acid 1a/MgF2 catalyst that enables effective catalysis of asymmetric Friedel-Crafts reactions of phenols with up to 82% yield and >99% ee is presented. A dramatic synergistic effect has been observed in the combinations of two types of acids, wherein a highly active binary-acid catalyst can be generated from two individually inert acids.