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Published on: January 3, 2018
Nucleophilicity of 4-(Alkylthio)-3-imidazoline Derived Enamines
Magenta J Hensinger1, Andreas Eitzinger1, Oliver Trapp1,2
1Department Chemie, Ludwig-Maximilians-Universtität München, Butenandtstrasse 5-13, 81377, München, Germany.
Abstract:
Imidazolidine-4-thiones (ITOs) are cyclic, secondary amines that were considered as potential prebiotic organocatalysts for light-driven α-alkylations of aldehydes by bromoacetonitrile (BAN). Recent studies showed that the initially supplied ITOs represent the pre-catalyst because they undergo S-alkylation with BAN to give 4-(alkylthio)-3-imidazolines (TIMs). Given that the same reagent mix that undergoes light-driven α-alkylations is also effective in the dark, we synthesized ten ITO- or TIM-derived enamines of aldehydes and characterized their nucleophilic reactivities by kinetic studies in acetonitrile. The experimental second-order rate constants k2 for reactions of enamines with benzhydrylium ions (reference electrophiles) were evaluated by the Mayr-Patz equation, lg k2 (20 °C)=sN (N+E). The determined nucleophilicities N (and sN ) reveal the reactivity profiles of these enamines under prebiotically relevant conditions as well as their potential for use in organocatalytic synthesis.
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