Electrocarboxylation of N-Acylimines with Carbon Dioxide: Access to Substituted α-Amino Acids

Abstract

Direct electrocarboxylation of various N-acylimines with atmospheric CO2 is achieved in an undivided cell under mild conditions, affording substituted α-amino acids in yields of 62–95%. This reaction is conducted with high efficiency using triethanolamine as an external reductant under nonsacrificial anode conditions, and can be facilely performed on gram scale. Preliminary mechanistic studies including cyclic voltammetry and control experiments support N-radical carbanion as the key intermediate.

Electrochemical CO2 Utilization for the Synthesis of α-Hydroxy Acids

“…The strong agitation might impair the second redox process, flushing away unstable intermediates. A distinct effect of mechanical stirring was also observed in other electro–organic reactions. , However, this would require a rather slow second reduction step, which contradicts the suggestions by Zhang and co-workers, who postulate an immediate second reduction step …”

“…The negative shift of the first reduction event in the presence of CO 2 has been observed in other carboxylation studies and could be a result of the consecutive reaction. 42,43 A remarkable effect of the purging gas was observed. In the absence of CO 2 , a second reduction peak (Red 2 ) accompanied by a third redox event (Red 3 and Ox) could be observed, which are not present in the CO 2saturated electrolyte.…”

“…61,62 However, this would require a rather slow second reduction step, which contradicts the suggestions by Zhang and co-workers, who postulate an immediate second reduction step. 42 To generalize the electrocarboxylation protocol, various aldehydes and ketones were subjected under conditions optimized for benzaldehyde as a starting material (Scheme 3). Graphite was chosen as a cathode material since it is nontoxic and environmentally benign, and the mandelic acid yield was only slightly smaller compared to lead.…”

Photocatalytic Cross-Pinacol Coupling

“…Similar effects of CO2 have been observed in the electrocarboxylation of ketones and imines with CO2. [31][32][33][34][35] We next performed DFT calculations on the reduction step to support the hypothesis that CO2 promotes the generation of carbinol anion species (Fig. 4d).…”

Recent advances in the electrochemically mediated chemical transformation of carbon dioxide

“…A range of substitution patterns and substituents on the ester can all In 2022, Zhang and colleagues also chose TEOA as the sacrificial reducing agent and proton source for electrocarboxylation (Scheme 30). 58 They developed an effective direct electrocarboxylation of various N-acylimines with atmospheric CO 2 , in an undivided cell with platinum as a cathode and anode, in DMF under a simple constant current condition of 10 mA cm À2 with 5.0 F mol À1 using triethanolamine as an additional sacrificial reducing agent, delivering substituted amino acids in good to excellent yields. N-Radical carbanion was proved to be the key intermediate by cyclic voltammetry and isotope labeling experiments.…”