Universität zu Köln

Paul, Mathias ORCID: 0000-0003-4635-3605, Peckelsen, Katrin, Thomulka, Thomas, Martens, Jonathan ORCID: 0000-0001-9537-4117, Berden, Giel ORCID: 0000-0003-1500-922X, Oomens, Jos ORCID: 0000-0002-2717-1278, Neudoerfl, Joerg-M., Breugst, Martin, Meijer, Anthony J. H. M., Schaefer, Mathias and Berkessel, Albrecht ORCID: 0000-0003-0470-7428 . Breslow Intermediates (Amino Enols) and Their Keto Tautomers: First Gas-Phase Characterization by IR Ion Spectroscopy. Chem.-Eur. J.. WEINHEIM: WILEY-V C H VERLAG GMBH. ISSN 1521-3765

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Abstract

Breslow intermediates (BIs) are the crucial nucleophilic amino enol intermediates formed from electrophilic aldehydes in the course of N-heterocyclic carbene (NHC)-catalyzed umpolung reactions. Both in organocatalytic and enzymatic umpolung, the question whether the Breslow intermediate exists as the nucleophilic enol or in the form of its electrophilic keto tautomer is of utmost importance for its reactivity and function. Herein, the preparation of charge-tagged Breslow intermediates/keto tautomers derived from three different types of NHCs (imidazolidin-2-ylidenes, 1,2,4-triazolin-5-ylidenes, thiazolin-2-ylidenes) and aldehydes is reported. An ammonium charge tag is introduced through the aldehyde unit or the NHC. ESI-MS IR ion spectroscopy allowed the unambiguous conclusion that in the gas phase, the imidazolidin-2-ylidene-derived BI indeed exists as a diamino enol, while both 1,2,4-triazolin-5-ylidenes and thiazolin-2-ylidenes give the keto tautomer. This result coincides with the tautomeric states observed for the BIs in solution (NMR) and in the crystalline state (XRD), and is in line with our earlier calculations on the energetics of BI keto-enol equilibria.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Paul, Mathias UNSPECIFIED orcid.org/0000-0003-4635-3605 UNSPECIFIED Peckelsen, Katrin UNSPECIFIED UNSPECIFIED UNSPECIFIED Thomulka, Thomas UNSPECIFIED UNSPECIFIED UNSPECIFIED Martens, Jonathan UNSPECIFIED orcid.org/0000-0001-9537-4117 UNSPECIFIED Berden, Giel UNSPECIFIED orcid.org/0000-0003-1500-922X UNSPECIFIED Oomens, Jos UNSPECIFIED orcid.org/0000-0002-2717-1278 UNSPECIFIED Neudoerfl, Joerg-M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Breugst, Martin UNSPECIFIED UNSPECIFIED UNSPECIFIED Meijer, Anthony J. H. M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Schaefer, Mathias UNSPECIFIED UNSPECIFIED UNSPECIFIED Berkessel, Albrecht UNSPECIFIED orcid.org/0000-0003-0470-7428 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-309920
DOI:	10.1002/chem.202003454
Journal or Publication Title:	Chem.-Eur. J.
Publisher:	WILEY-V C H VERLAG GMBH
Place of Publication:	WEINHEIM
ISSN:	1521-3765
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Chemistry > Institute of Organic Chemistry
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language CARBENE-CATALYZED UMPOLUNG; THIAMINE ACTION; BASIS-SETS; REACTIVITY; 1,3,4-TRIPHENYL-4,5-DIHYDRO-1H-1,2,4-TRIAZOL-5-YLIDENE; DISPERSION; MECHANISM Multiple languages Chemistry, Multidisciplinary Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/30992