Electroreductive Denitrogenation of Tetrazolo[1,5-a]quinoxalin-4(5H)-ones to 3-Aminoquinoxalin-2(1H)-ones

The denitrogenation of tetrazoles is typically performed using transition-metal catalysts at high temperatures due to the inherent stability of the tetrazole group. In this work, we present, for the first time, an electrochemical method for denitrogenating tetrazoles at room temperature. This method employs a sacrificial zinc anode and a platinum cathode in a solvent mixture of acetonitrile and water under a constant current in an undivided cell. The electroreductive conditions are mild, enabling the synthesis of primary amine-containing N-heterocycles in moderate to excellent yields, with a wide range of functional group compatibility. Notably, the concentration of the cosolvent H₂O is crucial for achieving optimal results; only two equiv are necessary for the best outcomes. However, increasing the concentration of H₂O leads to the generation of more hydroxide ions at the platinum cathode. These hydroxide ions can hydrolyze the amide groups in the substrates, resulting in tetrazolated anilines as the major products rather than the primary amines. The proposed mechanism is supported by cyclic voltammetry, control experiments, deuterium labeling experiments, and electrospray ionization–high-resolution mass spectrometry (ESI-HRMS) analyses. Additionally, we thoroughly discuss the role of the Zn²⁺ ions leaching from the oxidation of the anode.