Biomimetic Organocatalytic C–C-Bond Formations
87
Thus, the imidazolin-2-ylidene 87a synthesized by Arduengo et al.
in 1991 is now referred to as the first N-heterocyclic carbene to be isolated and characterized. Its preparation was achieved by deprotonation
of the corresponding imidazolium salt 91. Later, Arduengo et al. also
synthesized stable carbenes with less bulky substituents. It should be
noted that the structure of these carbenes is identical with the Wanzlick
carbenes. Progress in laboratory methods were finally decisive for the
successful isolation of these carbenes (Scheme 21).
Since Arduengo’s initial reports, numerous stable N-heterocyclic carbenes of various types have been synthesized (for reviews on the history
see: Arduengo and Kraftczyk 1998; see also Herrmann 2002; César
et al. 2004; Kauer Zinn et al. 2004; Díez-González and Nolan 2005;
Garrison and Youngs 2005; Tekavec and Louie 2007; for reviews see
Herrmann and Koecher 1997; Arduengo 1999; Bourissou et al. 2000;
Perry and Burgess 2003; Korotkikh et al. 2005; Hahn 2006). Applications in organocatalysis and metal-based catalysis have developed
rapidly.
Inspired by this success and based on our work on the asymmetric Stetter reaction in the late 1980s, our research group together with
that of Teles studied the triazole heterocycle as an alternative structure.
Scheme 21. Preparation of stable imidazolin-2-ylidenes by Arduengo et al.
Scheme 22. Synthesis of the stable carbene 94 developed by Enders, Teles et al.
87
Thus, the imidazolin-2-ylidene 87a synthesized by Arduengo et al.
in 1991 is now referred to as the first N-heterocyclic carbene to be isolated and characterized. Its preparation was achieved by deprotonation
of the corresponding imidazolium salt 91. Later, Arduengo et al. also
synthesized stable carbenes with less bulky substituents. It should be
noted that the structure of these carbenes is identical with the Wanzlick
carbenes. Progress in laboratory methods were finally decisive for the
successful isolation of these carbenes (Scheme 21).
Since Arduengo’s initial reports, numerous stable N-heterocyclic carbenes of various types have been synthesized (for reviews on the history
see: Arduengo and Kraftczyk 1998; see also Herrmann 2002; César
et al. 2004; Kauer Zinn et al. 2004; Díez-González and Nolan 2005;
Garrison and Youngs 2005; Tekavec and Louie 2007; for reviews see
Herrmann and Koecher 1997; Arduengo 1999; Bourissou et al. 2000;
Perry and Burgess 2003; Korotkikh et al. 2005; Hahn 2006). Applications in organocatalysis and metal-based catalysis have developed
rapidly.
Inspired by this success and based on our work on the asymmetric Stetter reaction in the late 1980s, our research group together with
that of Teles studied the triazole heterocycle as an alternative structure.
Scheme 21. Preparation of stable imidazolin-2-ylidenes by Arduengo et al.
Scheme 22. Synthesis of the stable carbene 94 developed by Enders, Teles et al.