How Electrophilic Are Keteniminium Ions?

Dedication

Dedicated to our friend and colleague Paul Knochel on the occasion of his 70th birthday.

Abstract

Keteniminium triflates (R₂C=C=NMe₂ ⁺ TfO⁻) react via classical electrophilic aromatic substitutions with electron-rich arenes forming Wheland intermediates that rapidly undergo triflate-catalyzed tautomerizations to enammonium ions. These ions do not isomerize to the thermodynamically more-stable iminium ions and can quantitatively be converted into the corresponding enamines by treatment with triethylamine. Kinetic studies of keteniminium attack at the arenes provided the electrophilicity parameters of the keteniminium ions E = −2.8 (for R = Me) and E = −1.9 (for R = Ph). These values quantify the one-bond electrophilic reactivity of keteniminium ions and allow us to derive the energy of concert of their [2 + 2]-cycloadditions with alkenes.

Keywords

Kinetics - Linear free energy relationships - Quantum-chemical calculations - Reaction mechanism - Acylation

Publikationsverlauf

Eingereicht: 05. Juni 2025

Angenommen nach Revision: 04. Juli 2025

Artikel online veröffentlicht:
13. August 2025

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