Enantioselective Michael Addition of 2-Hydroxy-1,4-naphthoquinone to β,γ-Unsaturated α-Keto Esters Catalyzed by Binaphthyl-Modified Squaramide

The structures of quinone and naphthoquinone exist in a large number of natural products and biologically active molecules.1 Particularly, many of these naturally occurring naphthoquinones and their synthetic analogues are important precursors for the synthesis of natural products and pharma-ceuticals.2 The Michael reaction is widely recognized as one of the most fascinating and powerful methods for the formation of C-C bonds in organic synthesis3 and the development of asymmetric version of this reaction has been the subject of intensive research.4 Enantioselective organocatalytic Michael addition of cyclic 1,3-dicarbonyl compounds to α,β-un-saturated carbonyl compounds represents a direct approach to chiral 1,5-dicarbonyl compounds that are versatile inter-mediates in organic synthesis.5 Recently, several groups have reported the asymmetric Michael addition of 2-hydroxy-1,4