Carbon dioxide as a multifunctional regulator in electrochemical vicinal bromination

Vicinal dibromination of alkenes is a fundamentally important transformation in organic synthesis, as vicinal dibromides are prevalent motifs in bioactive molecules and serve as indispensable intermediates across chemical synthesis. Despite extensive advances in thermal, photochemical, and electrochemical dibromination, the development of efficient and practical dibromination methods using inexpensive and readily available bromine sources remains highly desirable. In particular, N–H-containing substrates can present additional challenges under oxidative electrochemical conditions because of competing reactions involving the nitrogen functionality. Herein, we report a CO2-mediated electrochemical strategy that enables efficient and chemoselective vicinal dibromination of N–H-containing amino acid-derived alkenes as well as a broad range of functionalized alkenes using NaBr as the bromine source. Mechanistic studies indicate that CO2 plays multiple cooperative roles in this transformation: (i) in situ transient protection of N-H moieties, (ii) formation of carbonic acid with water to replace conventional protic acids, and (iii) lowering of the oxidation potential of bromide ions. Collectively, these findings demonstrate the multifunctional regulatory role of CO2 in the present electrochemical vicinal dibromination system. The authors report a CO2-mediated electrochemical vicinal dibromination, compatible with broad range of alkenes bearing sensitive functional groups, using NaBr as a sustainable bromine source.