Insights into the Mechanism of Anodic N–N Bond Formation by Dehydrogenative Coupling

The electrochemical synthesis of pyrazol­idine-3,5-diones and benz­oxazoles by N–N bond formation and C,O linkage, respectively, represents an easy access to medicinally relevant structures. Electrochemistry as a key technology ensures a safe and sustainable approach. We gained insights in the mechanism of these reactions by combining cyclo­voltammetric and synthetic studies. The electron-transfer behavior of anilides and dianilides was studied and led to the following conclusion: The N–N bond formation involves a diradical as intermediate, whereas the benz­oxazole formation is based on a cationic mechanism. Besides these studies, we developed a synthetic route to mixed dianilides as starting materials for the N–N coupling. The compatibility with valuable functionalities like triflates and mesylates for follow-up reactions as well as the comparison of different electrochemical set-ups also enhanced the applicability of this method.