Conjugate Umpolung of β,β-Disubstituted Enals by Dual Catalysis with an N-Heterocyclic Carbene and a Brønsted Acid: Facile Construction of Contiguous Quaternary Stereocenters

A sterically hindered homoenolate has been generated by the NHC‐catalyzed conjugate umpolung of β,β‐disubstituted enals and successfully employed in a facile stereoselective annulation with isatins. The strategy provides efficient access to spirocyclic oxindoles bearing two highly congested contiguous quaternary carbon centers. The use of a Brønsted acid cocatalyst was found to be crucial for guaranteeing both excellent reactivity and high stereoselectivity. Hey neighbor! A previously unreported conjugate umpolung of β,β‐disubstituted enals through NHC catalysis has been discovered, allowing the formation of products containing contiguous quaternary centers. Densely substituted spirocyclic oxindoles were readily prepared using a dual activation strategy.