Synlett 2014; 25(12): 1791-1792
DOI: 10.1055/s-0033-1378224
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© Georg Thieme Verlag Stuttgart · New York

N-Mesityl-Substituted Triazolium Salts

Egor Chirkin
Laboratoire de Pharmacognosie UMR CNRS 8638, Université Paris Descartes, 4 Avenue de l’Observatoire, 75006 Paris, France   Email: egor.chirkin@parisdescartes.fr
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Further Information

Publication History

Publication Date:
12 June 2014 (online)

Introduction

Metal-free organocatalysis employing N-heterocyclic carbenes (NHCs) has attracted great interest because of its use in the construction of intricate molecular architectures from simple starting materials under mild reaction conditions.[1] The catalytic pathway of NHCs mimics that of thiamine-dependent enzymatic processes and passes through discrete reactive species, such as acyl anions and enolate or homoenolate equivalents.[2] This enables the selective generation of a set of versatile electrophilic (acyl azoliums) and nucleophilic (enolates, homoenolates) intermediates and makes NHCs efficient catalysts in such various reactions as acylation, cycloaddition, β-borylation, and elimination.

N-Mesityl substituted imidazolium (cat. A) and triazolium (cat. B) salts were introduced by Bode and co-workers as stable NHC precursors.[3] The imidazolium derivative favors the homoenolate pathway, whereas the triazolium precursor promotes almost all NHC-catalyzed transformations, except for benzoin and Stetter reactions. Chiral pre-catalysts like C and its enantiomer are also commercially available.[4]

It should be noted that the N-substituent is of crucial importance; for example, an N-phenyl substituents might not provide any product, while the Bode (N-mesityl) or Rovis (N-pentafluorophenyl)[5] catalysts are highly catalytically active.

Zoom Image
Figure 1 N-Mesityl-substituted imidazolium (cat. A) and triazolium (cat. B and C) carbene precursors. Chiral pre-catalyst C is commercially available (Mes = 1,3,5-trimethylphenyl).
 
  • References

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