N-Heterocyclic Carbene-Catalyzed Generation of Homoenolates: Efficient Asymmetric Synthesis of Dispirocyclopentanones by Direct Annulation of Enals and Isoindigos

A highly efficient asymmetric (3+2) annulation between enals and isoindigos was achieved via the N-heterocyclic carbene-catalyzed addition of homoenolates to activated tetrasubstituted C=C double bonds. The protocol provided straightforward access to enantiomerically enriched dispirocyclopentanone bisoxindoles (up to 97% ee) with three contiguous stereocenters, two of which are highly congested vicinal all-carbon quaternary centers.