Wessels, Alina ORCID: 0000-0001-7915-5627, Klussmann, Martin ORCID: 0000-0002-9026-205X, Breugst, Martin, Schloerer, Nils E. and Berkessel, Albrecht (2022). Formation of Breslow Intermediates from N-Heterocyclic Carbenes and Aldehydes Involves Autocatalysis by the Breslow Intermediate, and a Hemiacetal. Angew. Chem.-Int. Edit., 61 (23). WEINHEIM: WILEY-V C H VERLAG GMBH. ISSN 1521-3773

Full text not available from this repository.

Abstract

Under aprotic conditions, the stoichiometric reaction of N-heterocyclic carbenes (NHCs) such as imidazolidin-2-ylidenes with aldehydes affords Breslow Intermediates (BIs), involving a formal 1,2-C-to-O proton shift. We herein report kinetic studies (NMR), complemented by DFT calculations, on the mechanism of this kinetically disfavored H-translocation. Variable time normalization analysis (VTNA) revealed that the kinetic orders of the reactants vary for different NHC-to-aldehyde ratios, indicating different and ratio-dependent mechanistic regimes. We propose that for high NHC-to-aldehyde ratios, the H-shift takes place in the primary, zwitterionic NHC-aldehyde adduct. With excess aldehyde, the zwitterion is in equilibrium with a hemiacetal, in which the H-shift occurs. In both regimes, the critical H-shift is auto-catalyzed by the BI. Kinetic isotope effects observed for R-CDO are in line with our proposal. Furthermore, we detected an H-bonded complex of the BI with excess NHC (NMR).

Item Type: Journal Article
Creators:
CreatorsEmailORCIDORCID Put Code
Wessels, AlinaUNSPECIFIEDorcid.org/0000-0001-7915-5627UNSPECIFIED
Klussmann, MartinUNSPECIFIEDorcid.org/0000-0002-9026-205XUNSPECIFIED
Breugst, MartinUNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Schloerer, Nils E.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Berkessel, AlbrechtUNSPECIFIEDUNSPECIFIEDUNSPECIFIED
URN: urn:nbn:de:hbz:38-670659
DOI: 10.1002/anie.202117682
Journal or Publication Title: Angew. Chem.-Int. Edit.
Volume: 61
Number: 23
Date: 2022
Publisher: WILEY-V C H VERLAG GMBH
Place of Publication: WEINHEIM
ISSN: 1521-3773
Language: English
Faculty: Unspecified
Divisions: Unspecified
Subjects: no entry
Uncontrolled Keywords:
KeywordsLanguage
THIAMINE ACTION; MECHANISM; CATALYSTS; UMPOLUNG; CONDENSATIONMultiple languages
Chemistry, MultidisciplinaryMultiple languages
URI: http://kups.ub.uni-koeln.de/id/eprint/67065

Downloads

Downloads per month over past year

Altmetric

Export

Actions (login required)

View Item View Item