Aldehyde Umpolung by N-Heterocyclic Carbenes: NMR Characterization of the Breslow Intermediate in its Keto Form, and a Spiro-Dioxolane as the Resting State of the Catalytic System

Aldehyde Umpolung by N-Heterocyclic Carbenes: NMR Characterization of the Breslow Intermediate in its Keto Form, and a Spiro-Dioxolane as the Resting State of the Catalytic System

Surprises from a classic: The Breslow intermediate of triazolylidene‐catalyzed benzoin condensations was characterized for the first time by NMR spectroscopy in its keto form (K, energetic minimum). The hitherto unknown spiro‐dioxolane S, generated from the carbene catalyst and two equivalents of al...

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Veröffentlicht in:Angewandte Chemie (International ed.) 2010-09, Vol.49 (39), p.7120-7124
Hauptverfasser: Berkessel, Albrecht, Elfert, Silvia, Etzenbach-Effers, Kerstin, Teles, J. Henrique
Format: Artikel
Sprache:eng
Schlagworte:
carbenes
NMR spectroscopy
organocatalysis
reaction mechanisms
umpolung
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Zusammenfassung:Surprises from a classic: The Breslow intermediate of triazolylidene‐catalyzed benzoin condensations was characterized for the first time by NMR spectroscopy in its keto form (K, energetic minimum). The hitherto unknown spiro‐dioxolane S, generated from the carbene catalyst and two equivalents of aldehyde, is the resting state of the catalytic system.
ISSN:1433-7851
1521-3773
DOI:10.1002/anie.200907275