Ytterbium triflate-catalyzed conjugate addition of β-ketoesters to activated 1,4-naphthoquinones

An efficient procedure for the conjugate addition of various β-ketoesters to activated 1,4-naphthoquinones using a catalytic amount of Yb(OTf)3 was developed. The tri-, tetra-, and pentacyclic adducts were obtained in very good to excellent yield. Cyclic β-ketoesters added smoothly to activated quinones when compared to their acyclic counterparts.