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 contiguo...

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Bibliographic Details
Published in:Angewandte Chemie International Edition 2014-09, Vol.53 (39), p.10515-10519
Main Authors: Li, Jun-Long, Sahoo, Basudev, Daniliuc, Constantin-G., Glorius, Frank
Format: Article
Language:English
Subjects:
Acids - chemistry
Aldehydes - chemistry
carbenes
Catalysis
Cycloaddition Reaction
dual catalysis
Heterocyclic Compounds - chemistry
Indoles - chemistry
Methane - analogs & derivatives
Methane - chemistry
quaternary centers
spiro compounds
Spiro Compounds - chemistry
Stereoisomerism
umpolung
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Summary: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.
ISSN:1433-7851
1521-3773
DOI:10.1002/anie.201405178