Catalytic Asymmetric Tandem Cycloisomerization/[5+2] Cycloaddition Reaction of N-Aryl Nitrone Alkynes with Methyleneindolinones.

An asymmetric tandem cycloisomerization and intermolecular [5+2] cycloaddition reaction of 2-ethynylphenyl-substituted nitrones with methyleneindolinones was realized. The process includes the palladium(II)-promoted in situ formation of azomethine ylide and the following chiral N,N'-dioxide-Co(II) complex-catalyzed regio-, diastereo-, and enantioselective [5+2] cycloaddition reaction. The desired spiro-tropanyl oxindoles were obtained in good yields with excellent dr and ee values. On the basis of the determination of the catalyst structure, a possible transition state model was proposed.