Why is phenyl azide so unreactive in [3 + 2] cycloaddition reactions? Demystifying Sustmann's paradigmatic parabola
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2023-09
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Facultad/escuela
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en
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Royal Society of Chemistry
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Attribution 3.0 Unported Deed (CC BY 3.0)
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https://creativecommons.org/licenses/by/3.0/
Resumen
The [3 + 2] cycloaddition (32CA) reactions of phenyl azide with a series of 25 ethylenes of different electronic activation have been studied within Molecular Electron Density Theory (MEDT) at the ωB97X-D/6-311G(d,p) computational level to understand the low reactivity of azides participating in 32CA reactions. Analysis of the reactivity indices allows characterizing phenyl azide as a moderate electrophile and a moderate nucleophile. The relative reaction rate constants kr of twelve selected 32CA reactions, together with the electrophilicity ω and nucleophilicity N indices of the corresponding ethylenes, allow us to classify these 32CA reactions into four groups: (i) group A, involving supernucleophilic ethylenes and displaying a kr > 104; (ii) group B, involving strained cyclic ethylenes and displaying a kr < 102; (iii) group C, involving strongly electrophilic ethylenes and displaying a kr ≤ 102, and (iv) group D, involving moderately electrophilic and nucleophilic ethylenes and displaying a kr < 2. These four groups are characterized in Sustmann's “parabolic correlation”, which results from an inaccurate interpretation of the reactivity of phenyl azide, which is not an “ambiphilic species” but rather a moderate electrophile that reacts efficiently only with supernucleophilic ethylenes in reverse electron density flux (REDF) zw-type 32CA reactions. © 2023 The Royal Society of Chemistry.
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Indexación: Scopus
Palabras clave
Carrier Concentration, Computation Theory, Cycloaddition, Electron Density Measurement, Molecular Electron Density Theory (MEDT)
Citación
Organic Chemistry Frontiers. Volume 10, Issue 22, Pages 5579 - 5591. 26 September 2023
DOI
10.1039/d3qo00811h