Issue 11, 2007
From the journal:

Organic & Biomolecular Chemistry

Mayr electrophilicity predicts the dual Diels–Alder and σ-adduct formation behaviour of heteroaromatic super-electrophiles

Sami Lakhdar,a   Régis Goumont,a   François Terrier,*a   Taoufik Boubaker,b   Julian M. Dustc  and  Erwin Buncel*d  

* Corresponding authors

a Institut Lavoisier de Versailles, UMR CNRS 8180, Université de Versailles, 45 Avenue des Etats-Unis, 78035-Versailles Cedex, France

b Unité de Recherche de Physico-Chimie Moléculaire, Faculté des Sciences de Monastir, Avenue de l’Environnement, 5019 Monastir, Tunisie

c Department of Chemistry, Sir Wilfred Grenfell College, Memorial University of NewFoundland, Corner Brook, NF, Canada

d Department of Chemistry, Queen’s University, Kingston, ON, Canada

Abstract

We report on the dual reactivity, i.e. anionic Meisenheimer sigma adduct formation and Diels–Alder adduct formation, of a series of heteroaromatic super-electrophiles, including 4,6-dinitro-benzofuroxan, -N-arylbenzotriazoles (4), -benzothiadiazole and -benzoselenadiazole. Measured pKaH2O values for sigma adduct formation provide a quantitative measure of super-electrophilic reactivity with a satisfactory correlation between the Mayr E electrophilicity parameter and pKaH2O:E = −0.662 pKaH2O (or pKR+) −3.20 (r2 = 0.987)The most highly electrophilic, pre-eminent super-electrophile is 4,6-dinitrotetrazolopyridine (E = −4.67, pKaH2O = 0.4), which supercedes the reference Meisenheimer super-electrophile, 4,6-dinitrobenzofuroxan (E = −5.06, pKa = 3.75), having itself an E value superior by 8 orders of magnitude compared to 1,3,5-trinitrobenzene as the benchmark normal Meisenheimer electrophile (E = −13.19, pKaH2O = 13.43). (For relevant kinetic parameters as well as E and pKa values, see Table 1.) In a parallel study we have investigated Diels–Alder (normal and inverse electron demand) reactivity of this series of heteroaromatic electrophiles and have shown that Mayr E values are valid predictors of whether DA adducts will form and how rapidly. The observed order of pericyclic reactivity corresponds to E = −8.5 as the demarcation E value, in close agreement with sigma complexation; thus pointing to a common origin for the two processes, i.e. an inverse relationship between the degree of aromaticity of the carbocyclic ring and ease of sigma complexation, or DA reactivity, respectively.

Graphical abstract: Mayr electrophilicity predicts the dual Diels–Alder and σ-adduct formation behaviour of heteroaromatic super-electrophiles

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Article information

DOI
https://doi.org/10.1039/B702060K
Article type
Paper
Submitted
08 Feb 2007
Accepted
05 Apr 2007
First published
30 Apr 2007

Org. Biomol. Chem., 2007,5, 1744-1751

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Mayr electrophilicity predicts the dual Diels–Alder and σ-adduct formation behaviour of heteroaromatic super-electrophiles

S. Lakhdar, R. Goumont, F. Terrier, T. Boubaker, J. M. Dust and E. Buncel, Org. Biomol. Chem., 2007, 5, 1744 DOI: 10.1039/B702060K

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