Universität zu Köln

Biswas, Animesh ORCID: 0000-0003-1073-3593, Neudoerfl, Jorg-M, Schlorer, Nils E. and Berkessel, Albrecht (2021). Acyl Donor Intermediates in N-Heterocyclic Carbene Catalysis: Acyl Azolium or Azolium Enolate? Angew. Chem.-Int. Edit., 60 (9). S. 4507 - 4512. WEINHEIM: WILEY-V C H VERLAG GMBH. ISSN 1521-3773

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Abstract

Azolium enolates and acyl azolium cations have been proposed as intermediates in numerous N-heterocyclic carbene (NHC) catalyzed transformations. Acetyl azolium enolates were generated from the reaction of 2-propenyl acetate with both saturated (SIPr) and aromatic (IPr) NHCs, isolated, and characterized (NMR, XRD). Protonation with triflic acid gave the corresponding acetyl azolium triflates which were isolated and characterized (NMR, XRD). Acyl azolium cations have been proposed as immediate precursors of the ester product, for example, in the redox esterification of alpha,beta-enals. Studies with d(3)-acetyl azolium triflate suggest that ester formation originates instead from an azolium enolate intermediate. Furthermore, the acetyl azolium enolate selectively reacted with alcohol nucleophiles in the presence of amines. While the acetyl azolium cation did not react with alcohols, an ester-selective reaction was induced by addition of base, by intermediate formation of the acetyl azolium enolate.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Biswas, Animesh UNSPECIFIED orcid.org/0000-0003-1073-3593 UNSPECIFIED Neudoerfl, Jorg-M UNSPECIFIED UNSPECIFIED UNSPECIFIED Schlorer, Nils E. UNSPECIFIED UNSPECIFIED UNSPECIFIED Berkessel, Albrecht UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-565755
DOI:	10.1002/anie.202010348
Journal or Publication Title:	Angew. Chem.-Int. Edit.
Volume:	60
Number:	9
Page Range:	S. 4507 - 4512
Date:	2021
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:	Keywords Language ORGANOCATALYTIC ACTIVATION; CHEMOSELECTIVE ACYLATION; THIAMINE ACTION; UMPOLUNG; ESTERS; GENERATION; MECHANISM; EQUIVALENTS; REACTIVITY; ALDEHYDES Multiple languages Chemistry, Multidisciplinary Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/56575