Highly Enantioselective Organocatalytic Michael Addition of 2-Hydroxy-1,4-naphthoquinone to β,γ-Unsaturated α-Oxo Esters

An organocatalytic enantioselective Michael addition of 2-hydroxy-1,4-naphthoquinone to beta,gamma-unsaturated alpha-oxo esters has been developed. The process was promoted by bifunctional chiral amine derived squaramides according to a hydrogen-bonding mediated activation mechanism and afforded the chiral adducts in high yields (up to 88%) and excellent enantioselectivity (up to 98% ee) under mild conditions. This organocatalytic asymmetric Michael addition provides an efficient route toward the synthesis of optically active functionalized naphthoquinones.