Hydrogen-bond-directed formal [5 + 1] annulations of oxindoles with ester-linked bisenones: facile access to chiral spirooxindole δ-lactones.

A novel bifunctional thiourea catalyzed formal [5 + 1] cycloaddition of oxindoles and ester-linked bisenones was successfully developed. This strategy involves two sequential Michael additions, leading to spirooxindole δ-lactones with three contiguous stereocenters including an all-carbon quaternary center with high diastereo- and enantioselectivites. In addition, a remarkable N-substituent effect was observed on the reactivity and selectivity.