Nucleophilic Carbenes as Organocatalysts
N-Heterocyclic carbenes (NHC) have become an important class of organocatalysts and class of ligands for transition-metal catalysis. In organocatalyzed umpolung reactions, thiazolium salt-derived NHC have been used successfully for decades. Even so, during recent years there has been an increased interest in NHC-catalyzed transformations and many new reactions have been developed. This article focuses on the use of NHC in the conjugate umpolung of α,β-unsaturated aldehydes.
KeywordsCarbene Carbon Single Diastereomer Benzoin Condensation Azolium Salt Unfavorable Steric Interaction
Generous financial support by the Deutsche Forschungsgemeinschaft (Priority program organocatalysis), the Fonds der Chemischen Industrie (Dozentenstipendium for F.G.), the Deutsche Akademische Austauschdienst (fellowship for K.H.) and the BASF AG (BASF Catalysis Award to F.G.) as well as donations by Bayer AG are gratefully acknowledged. In addition, the research of F.G. was also generously supported by the Alfried Krupp Prize for Young University Teachers of the Alfried Krupp von Bohlen und Halbach Foundation.
- Berkessel A, Gröger H (2004) Asymmetric Organocatalysis. VCH, WeinheimGoogle Scholar
- Nolan SP (ed) (2006) N-Heterocyclic carbenes in synthesis. Wiley-VCH, WeinheimGoogle Scholar
- Pesch J, Harms K, Bach T (2004) Preparation of axially chiral N,N′-diarylimidazolium and N-arylthiazolium salts and evaluation of their catalytic potential in the benzoin and in the intramolecular stetter reactions. Eur J Chem 9:2025–2035Google Scholar