Chemoselective, Metal-free, (Hetero)Arene Electroreduction Enabled by Rapid Alternating Polarity

Arene semi-reduction remains a challenge when multiple re-ductively labile functional groups are present or when using heteroarene substrates. Conventional chemical and even elec-trochemical Birch-type reductions suffer from a lack of chemoselectivity due to a reliance on alkali metals or harshly reducing conditions. This study reveals that a simpler avenue is available for such reductions by simply altering the wave-form of current delivery, namely rapid alternating polarity (rAP). The developed method, which proceeds in protic sol-vent and can be easily scaled up, does not require any metal additives or stringently anhydrous conditions. The scope of this dearomatization is broad, tolerating numerous functional groups and providing rapid access to previously challenging molecules. While the mechanism has not been fully deci-phered, the key feature of the rAP reduction is that the main competing process, namely proton reduction, can be sup-pressed. As such, unique arene reductions can be accom-plished even outside solvent electrochemical window or in the presence of Brønsted acids.