Nucleophilic reactivities of Schiff base derivatives of amino acids

Timofeeva, Dada S.; Ofial, Armin R. und Mayr, Herbert (2019): Nucleophilic reactivities of Schiff base derivatives of amino acids. In: Tetrahedron, Bd. 75, Nr. 4: S. 459-463

Abstract

Treatment of alpha-imino esters derived from glycine esters and benzophenone or benzaldehydes with potassium tert butoxide in DMSO gave persistent solutions of carbanions at 20 degrees C. The kinetics of their reactions with quinone methides and benzylidene malonates (reference electrophiles) have been followed photometrically under pseudo-first order conditions. The reactions followed second-order rate laws. Since addition of 18-crown-6 ether did not affect the reaction rates, the measured rate constants correspond to the reactions of the non-paired carbanions. Plots of the second-order rate constants against the electrophilicity parameters E of the electrophiles are linear, which allowed us to derive the nucleophile-specific parameters N and s(N), according to the linear Gibbs energy relationship lg k(2)(20 degrees C) = s(N)(N + E). The Ph2C = N- and PhCH = N- groups act as very weak electron acceptors with the consequence that Ph2C = N-CH--CO2R and PhCH = N-CH--CO2R have a similar nucleophilicity as Ph-CH--CO2Et, the anion of ethyl phenylacetate. (C) 2018 Elsevier Ltd. All rights reserved.

• Dokumententyp: Zeitschriftenartikel
• Fakultät: Chemie und Pharmazie > Department Chemie
• Themengebiete: 500 Naturwissenschaften und Mathematik > 540 Chemie
• ISSN: 0040-4020
• Sprache: Englisch