Asymmetric Electrochemical Alkenylation by Synergistic Chiral Primary Amine and Naphthalene Catalysis

Abstract

External tuning of enamine intermediate has significantly expanded reaction space of typical aminocatalysis. Notwithstanding the progress of chemo- and photo-oxidation of enamine intermediate, electro-oxidation was left as a much less explored area, in stark contrast to the prosperous renaissance of electrochemistry in recent years. Challenges mainly come from the reactivity barrier as a consequence of heterogeneous electron transfer, and subtle stereo-control in ionic electrolyte solution under the influence of electric field. Herein, we report asymmetric α-alkenylation of carbonyl compounds using potassium alkenyl trifluoroborate as a model reaction to demonstrate the capability of primary amine catalysis under electrochemical conditions. By employing enamine redox mediator mapping (e-RM2) strategy, a new organic mediator, dimethoxyl naphthalene, was found to greatly enhance reactivity. Mechanistic studies uncover an ion-pair interaction between protonated aminocatalyst and anionic substrate that account for the exceptional enantioselectivity. This catalytic system demonstrates the best level of enantioselectivities in electro-oxidative enamine transformations so far.