Ernst Schering Foundation Symposium Proceedings, Vol. 2, pp. 159–181
DOI 10.1007/2789_2008_081
© Springer-Verlag Berlin Heidelberg
Published Online: 30 April 2008
Nucleophilic Carbenes as Organocatalysts
F. Glorius
(u) , K. Hirano
Organisch Chemisches Institut, Westfälische Wilhelms-Universität Münster,
Corrensstraße 40, 48149 Münster, Germany
email: glorius@uni-muenster.de
1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
2
Conjugate Umpolung . . . . . . . . . . . . . . . . . . . . . . . . 163
3
Mechanistic Proposal . . . . . . . . . . . . . . . . . . . . . . . . 166
4
Ketones and Imines as Electrophiles . . . . . . . . . . . . . . . . 167
5
Conjugate Umpolung of Crotonaldehyde Derivatives . . . . . . . . 169
6
Conjugate Umpolung of α-Substituted Cinnamaldehyde Derivatives 170
7
Intramolecular Variants . . . . . . . . . . . . . . . . . . . . . . . 172
8
Formation of β-Lactones . . . . . . . . . . . . . . . . . . . . . . 174
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
Abstract. 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.
1
Introduction
For many years, carbenes seemed to be elusive compounds and their
isolation appeared impossible. Therefore, the first isolation and characterization of a free N-heterocyclic carbene (NHC) in 1991 marked a true
DOI 10.1007/2789_2008_081
© Springer-Verlag Berlin Heidelberg
Published Online: 30 April 2008
Nucleophilic Carbenes as Organocatalysts
F. Glorius
(u) , K. Hirano
Organisch Chemisches Institut, Westfälische Wilhelms-Universität Münster,
Corrensstraße 40, 48149 Münster, Germany
email: glorius@uni-muenster.de
1
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
2
Conjugate Umpolung . . . . . . . . . . . . . . . . . . . . . . . . 163
3
Mechanistic Proposal . . . . . . . . . . . . . . . . . . . . . . . . 166
4
Ketones and Imines as Electrophiles . . . . . . . . . . . . . . . . 167
5
Conjugate Umpolung of Crotonaldehyde Derivatives . . . . . . . . 169
6
Conjugate Umpolung of α-Substituted Cinnamaldehyde Derivatives 170
7
Intramolecular Variants . . . . . . . . . . . . . . . . . . . . . . . 172
8
Formation of β-Lactones . . . . . . . . . . . . . . . . . . . . . . 174
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
Abstract. 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.
1
Introduction
For many years, carbenes seemed to be elusive compounds and their
isolation appeared impossible. Therefore, the first isolation and characterization of a free N-heterocyclic carbene (NHC) in 1991 marked a true