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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

Authors


  • Generous financial support by the Alexander von Humboldt Foundation (J.-L.L.), the European Research Council under the European Community’s Seventh Framework Program (FP7 2007–2013/ERC Grant agreement no. 25936), the DFG (Leibniz award), and NRW Graduate School of Chemistry (B.S.) is gratefully acknowledged. We also thank Dr. Matthew N. Hopkinson for helpful discussions.

Abstract

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.

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