Tunable System for Electrochemical Reduction of Ketones and Phthalimides

Abstract

Main observation and conclusion Herein, we report an efficient, tunable system for electrochemical reduction of ketones and phthalimides at room temperature without the need for stoichiometric external reductants. By utilizing NaN3 as the electrolyte and graphite felt as both the cathode and the anode, we were able to selectively reduce the carbonyl groups of the substrates to alcohols, pinacols, or methylene groups by judiciously choosing the solvent and an acidic additive. The reaction conditions were compatible with a diverse array of functional groups, and phthalimides could undergo one‐pot reductive cyclization to afford products with indolizidine scaffolds. Mechanistic studies showed that the reactions involved electron, proton, and hydrogen atom transfers. Importantly, an N3/HN3 cycle operated as a hydrogen atom shuttle, which was critical for reduction of the carbonyl groups to methylene groups.

Counter Electrode Reactions—Important Stumbling Blocks on the Way to a Working Electro‐organic Synthesis

“…Sodium azide, used as a supporting electrolyte, was shown to have a positive effect on the oxidation of formic acid, as the electron transfer was enforced. When acetic acid was used instead of formic acid, diphenylmethanol was found as the main product from the hydrogenation of benzophenone [110] …”

“…When acetic acid was used instead of formic acid, diphenylmethanol was found as the main product from the hydrogenation of benzophenone. [110] Another non-green but practical laboratory solution is the oxidation of sterically hindered amines. Xiang and coworkers reported the reduction of cyclic imides to hydroxylactams (Scheme 21).…”

Reaktionen an der Gegenelektrode – wichtige Stolpersteine auf dem Weg einer funktionierenden elektro‐organischen Synthese

“…Bei Verwendung von Essigsäure anstelle von Ameisensäure wird Diphenylmethanol aus der Hydrierung von Benzophenon als Hauptprodukt beobachtet. [110] Eine weitere nicht nachhaltige, aber praktische Laborlösung ist die Oxidation von sterisch gehinderten Aminen. es ist sehr sauer und bildet nach dem Protonenaustausch mit dem Lösungsmittel neutrale Radikale.…”

“…Es hat sich gezeigt, dass Natriumazid als Leitsalz einen positiven Effekt auf die Oxidation von Formiat hat, da der Elektronentransfer bevorzugt wird. Bei Verwendung von Essigsäure anstelle von Ameisensäure wird Diphenylmethanol aus der Hydrierung von Benzophenon als Hauptprodukt beobachtet [110] …”

Electrochemical formal homocoupling of sec-alcohols

“…Thus, the development of a sacrificial anode-free process such as paired electrolysis would be highly desirable [40][41][42][43][44]. The group of Wang recently reported the sacrificial anode-free electroreduction of benzophenone derivatives to afford vic-1,2-diols using over-stoichiometric NaN 3 under acidic conditions, but appropriate precau-tions should be taken for in situ-generated explosive and toxic HN 3 [45]. Kim et al reported the formation of vic-1,2-diols in the sacrificial anode-free electrocarboxylation of 1-phenylethanol and benzyl alcohol which involves tetramethylpiperidine-1-oxyl-mediated alcohol oxidation as an anodic event [46].…”