Chemoselective Electrosynthesis Using Rapid Alternating Polarity

Challenges in the selective manipulation of functional groups (chemoselectivity) in organic synthesis have historically been overcome using either reagents/catalysts that tunably interact with a substrate or through modification to shield undesired sites of reactivity (protecting groups). Although electrochemistry offers precise redox control to achieve unique chemoselectivity, this approach often becomes challenging in the presence of multiple redox-active functionalities. Historically, electrosynthesis has been performed almost solely by using direct current (DC). In contrast, utilization of alternating current (AC) has been considered as an option to improve reaction efficiency rather than a way to achieve distinctly different reaction outcomes. Here we show how a unique type of waveform employed to deliver electric current – rapid alternating polarity (rAP) – enables control over reaction outcomes in the chemoselective reduction of carbonyl compounds, one of the most widely used reaction manifolds. The reactivity observed cannot be recapitulated using DC electrolysis or chemical reagents. The synthetic value brought by this new method for controlling chemoselectivity is vividly demonstrated in the context of classical reactivity problems such as chiral auxiliary removal and cutting-edge medicinal chemistry topics such as the synthesis of PROTACs.