An Unexpected [3 + 2]-Cycloaddition between Spiro-Epoxyoxindoles and γ-Deconjugated Butenolides Catalyzed by Sc(OTf)3

A unique β-position [3 + 2]-cycloaddition between γ-deconjugated butenolides and spiro-epoxyoxindoles catalyzed by Sc(OTf)₃ has been disclosed. A variety of unexpected [3 + 2]-cycloaddition adducts of spiro-oxindoles fused with bicyclic γ-lactones and three consecutive stereocenters have been successfully constructed in good yields (up to 88%) with excellent diastereoselectivities (>20:1) in one single operation under mild conditions, which is difficult to achieve by traditional strategies.