Metal Enolates – Enamines – Enol Ethers: How Do Enolate Equivalents Differ in Nucleophilic Reactivity?

Artem I. Leonov; Daria S. Timofeeva; Armin R. Ofial; Herbert Mayr

doi:10.1055/s-0037-1611634

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CC BY ND NC 4.0 · Synthesis 2019; 51(05): 1157-1170
DOI: 10.1055/s-0037-1611634

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Metal Enolates – Enamines – Enol Ethers: How Do Enolate Equivalents Differ in Nucleophilic Reactivity?

Authors

Artem I. Leonov
Daria S. Timofeeva
Armin R. Ofial *

Department Chemie, Ludwig-Maximilians-Universität München, Butenandtstraße 5–13, 81377 München, Germany Email: ofial@lmu.de Email: Herbert.mayr@cup.lmu.de
Herbert Mayr *

Department Chemie, Ludwig-Maximilians-Universität München, Butenandtstraße 5–13, 81377 München, Germany Email: ofial@lmu.de Email: Herbert.mayr@cup.lmu.de

Abstract

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A contribution of Physical Organic Chemistry to systematizing Organic Synthesis. Cordial congratulations on the occasion of the Golden Anniversary of Synthesis.

Published as part of the 50 Years SYNTHESIS – Golden Anniversary Issue

Abstract

The kinetics of the reactions of trimethylsilyl enol ethers and enamines (derived from deoxybenzoin, indane-1-one, and α-tetralone) with reference electrophiles (p-quinone methides, benzhydrylium and indolylbenzylium ions) were measured by conventional and stopped-flow photometry in acetonitrile at 20 °C. The resulting second-order rate constants were subjected to a least-squares minimization based on the correlation equation lg k = s _N(N + E) for determining the reactivity descriptors N and s _N of the silyl enol ethers and enamines. The relative reactivities of structurally analogous silyl enol ethers, enamines, and enolate anions towards carbon-centered electrophiles are determined as 1, 10⁷, and 10¹⁴, respectively. A survey of synthetic applications of enolate ions and their synthetic equivalents shows that their behavior can be properly described by their nucleophilicity parameters, which therefore can be used for designing novel synthetic transformations.

Key words

alkylation - enols - kinetics - linear free energy relationship - reactivity scales

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References

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