Breslow Intermediates from Aromatic N‐Heterocyclic Carbenes (Benzimidazolin‐2‐ylidenes,Thiazolin‐2‐ylidenes) |
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| Authors: | Dr Mathias Paul Dr Nils E Schlörer Dr Jörg‐M Neudörfl Prof Dr Albrecht Berkessel |
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| Affiliation: | 1. www.berkessel.de
0000-0003-4635-3605
Cologne University, Department of Chemistry, Organic Chemistry, Cologne, Germany;2. Cologne University, Department of Chemistry, Organic Chemistry, Cologne, Germany |
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| Abstract: | We report the first generation and characterization of elusive Breslow intermediates derived from aromatic N‐heterocyclic carbenes (NHCs), namely benzimidazolin‐2‐ylidenes (NMR, X‐ray analysis) and thiazolin‐2‐ylidenes (NMR). In the former case, the diamino enols were generated by reaction of the free N,N‐bis(2,6‐diisopropylphenyl)‐ and N,N‐bis(mesityl)‐substituted benzimidazolin‐2‐ylidenes with aldehydes while the dimer of 3,4,5‐trimethylthiazolin‐2‐ylidene served as the starting material in the latter case. The unambiguous NMR identification of the first thiazolin‐2‐ylidene‐based Breslow intermediate rests on double 13C labeling of both the NHC and the aldehyde component. The acyl anion reactivity was confirmed by benzoin formation with excess aldehyde. |
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| Keywords: | Breslow intermediates carbenes NMR spectroscopy reaction mechanisms umpolung |
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