Paul, Mathias, Breugst, Martin ORCID: 0000-0003-0950-8858, Neudoerfl, Joerg-Martin, Sunoj, Raghavan B. and Berkessel, Albrecht (2016). Keto-Enol Thermodynamics of Breslow Intermediates. J. Am. Chem. Soc., 138 (15). S. 5044 - 5052. WASHINGTON: AMER CHEMICAL SOC. ISSN 1520-5126

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Abstract

Breslow intermediates, first postulated in 1958) are pivotal intermediates in carbene-catalyzed umpolung. Attempts to, isolate and characterize these fleeting amino enol species first met with success in 2012 when we found that saturated bis-Dip/Mes imidazolidinylidenes readily form isolable, though reactive diamino enols with aldehydes and enals. In contrast, triazolylidenes, upon stoichiometric reaction with aldehydes, :gave exclusively the keto tautomer, and no isolable enol. Herein, we present the synthesis of the missing keto tautomers of imidazolidinylidene-derived diamino enols, and computational thermodynamic data for 15 enol ketone pairs derived, from various carbenes/aldehydes. Electron-with-drawing substituents on the aldehyde favor enol formation, the same holds for N,N'-Dipp [2,6-di(2-propyl)phenyl] and N,N'-Mes [2,4,6-trimethylphenyl] substitution on the carbene component. The latter effect rests on stabilization of the diamino enol tautomer by Dipp substitution, and could be-attributed to dispersive interaction of the 2-propyl groups with the enol moiety. For three enol-ketone pairs, equilibration of the, thermodynamically disfavored tautomer was attempted, with acids and bases but could not be effected, indicating kinetic inhibition of proton transfer.

Item Type: Journal Article
Creators:
CreatorsEmailORCIDORCID Put Code
Paul, MathiasUNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Breugst, MartinUNSPECIFIEDorcid.org/0000-0003-0950-8858UNSPECIFIED
Neudoerfl, Joerg-MartinUNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Sunoj, Raghavan B.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Berkessel, AlbrechtUNSPECIFIEDUNSPECIFIEDUNSPECIFIED
URN: urn:nbn:de:hbz:38-278430
DOI: 10.1021/jacs.5b13236
Journal or Publication Title: J. Am. Chem. Soc.
Volume: 138
Number: 15
Page Range: S. 5044 - 5052
Date: 2016
Publisher: AMER CHEMICAL SOC
Place of Publication: WASHINGTON
ISSN: 1520-5126
Language: English
Faculty: Unspecified
Divisions: Unspecified
Subjects: no entry
Uncontrolled Keywords:
KeywordsLanguage
N-HETEROCYCLIC CARBENES; LONDON DISPERSION; THIAMINE ACTION; M06 SUITE; UMPOLUNG; STABILITY; MECHANISM; CONTINUUM; GENERATION; REACTIVITYMultiple languages
Chemistry, MultidisciplinaryMultiple languages
Refereed: Yes
URI: http://kups.ub.uni-koeln.de/id/eprint/27843

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