A facile access to indigodianiles

Bis ‐imidoylchlorides derived from oxalic acid can easily be transformed into the corresponding bis ‐imino benzotriazoles. The fact that benzotriazole is a well‐established leaving group has been exploited for an improved synthesis of indigodianiles. Employing metallic lithium, the benzotriazoles can be converted in a cascade reaction into indigo bis ‐arylimines in yields up to 45%. Formation of the reduced form of dimeric isocyanides is suggested as a key step.