Universität zu Köln

Harnying, Wacharee ORCID: 0000-0003-1538-4177, Sudkaow, Panyapon, Biswas, Animesh ORCID: 0000-0003-1073-3593 and Berkessel, Albrecht (2021). N-Heterocyclic Carbene/Carboxylic Acid Co-Catalysis Enables Oxidative Esterification of Demanding Aldehydes/Enals, at Low Catalyst Loading. Angew. Chem.-Int. Edit., 60 (36). S. 19631 - 19637. WEINHEIM: WILEY-V C H VERLAG GMBH. ISSN 1521-3773

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Abstract

We report the discovery that simple carboxylic acids, such as benzoic acid, boost the activity of N-heterocyclic carbene (NHC) catalysts in the oxidative esterification of aldehydes. A simple and efficient protocol for the transformation of a wide range of sterically hindered alpha- and beta-substituted aliphatic aldehydes/enals, catalyzed by a novel and readily accessible N-Mes-/N-2,4,6-trichlorophenyl 1,2,4-triazolium salt, and benzoic acid as co-catalyst, was developed. A whole series of alpha/beta-substituted aliphatic aldehydes/enals hitherto not amenable to NHC-catalyzed esterification could be reacted at typical catalyst loadings of 0.02-1.0 mol %. For benzaldehyde, even 0.005 mol % of NHC catalyst proved sufficient: the lowest value ever achieved in NHC catalysis. Preliminary studies point to carboxylic acid-induced acceleration of acyl transfer from azolium enolate intermediates as the mechanistic basis of the observed effect.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Harnying, Wacharee UNSPECIFIED orcid.org/0000-0003-1538-4177 UNSPECIFIED Sudkaow, Panyapon UNSPECIFIED UNSPECIFIED UNSPECIFIED Biswas, Animesh UNSPECIFIED orcid.org/0000-0003-1073-3593 UNSPECIFIED Berkessel, Albrecht UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-562194
DOI:	10.1002/anie.202104712
Journal or Publication Title:	Angew. Chem.-Int. Edit.
Volume:	60
Number:	36
Page Range:	S. 19631 - 19637
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 CARBENE NHC; STEREOSELECTIVE-SYNTHESIS; CHEMOSELECTIVE ACYLATION; ACTIVATED CARBOXYLATES; COOPERATIVE CATALYSIS; KINETIC RESOLUTION; AEROBIC OXIDATION; THIAMINE ACTION; ALCOHOLS; ESTERS Multiple languages Chemistry, Multidisciplinary Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/56219