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.