Chiral Squaramide Catalyzed Enantioselective Michael Addition of Cyclic 1,3-Diketones to β,γ-Unsaturated α-Keto Esters

A stereoselective methodology was developed to construct synthetically and pharmaceutically useful chiral chromene derivatives.In the presence of a newly designed bifunctional tertiary amine-squaramide organocatalyst,the Michael addition between cyclic 1,3-diketones and β,γ-unsaturated α-ketoesters occurred smoothly to provide the desired products with high to excellent yields(84％～97％)and enantioselectivies(79％～97％ee).This catalytic protocol was compatible with a range of structurally distinct β,γ-unsaturated α-ketoesters.