Asymmetric Catalytic Diverse Ring Opening/Cycloadditions of Cyclobutenones with (E)-Alkenyloxindoles and (E)-Dioxopyrrolidines.

Highly enantioselective ring-opening/cycloaddition reactions of cyclobutenones were achieved by employing chiral N,N'-dioxide/metal complexes as the catalysts. The Diels-Alder type cycloaddition with (E)-alkenyloxindoles yielded spirocyclohexaneoxindoles with excellent results. Meanwhile, a hetero-Diels-Alder process occurred with (E)-dioxopyrrolidines to afford spiropyrrolidinone-dihydropyranone derivatives.