Metal-free Knorr pyrrole synthesis by electrochemical reduction of oximes using carbon-based electrodes

A new variation of the Knorr pyrrole synthesis was developed, which proceeds by the cathodic reduction of readily available oximes. In contrast to existing methodologies, the developed system remains completely metal-free by employing reusable carbon-based electrodes, greatly improving sustainability. In addition, the supporting electrolyte is formed in situ from inexpensive acetic acid and triethylamine. This protocol is easy to conduct in a simple two-electrode divided cell set-up under constant current conditions and provides direct access to a broad range of highly substituted pyrroles. The broad functional group tolerance was demonstrated on 48 diverse examples with up to 87% yield including precursors of highly relevant APIs. Furthermore, the applicability of the method was demonstrated by a gram-scale electrolysis.