Electrochemical Direct Benzylic C–H Hydroxylation with H2O Enabled by an Unusual Dual Hydrogen-bonding Interaction

Minimizing side reactions is essential for achieving high yield and selectivity in organic synthesis, yet controlling overoxidation in direct benzylic C–H bond hydroxylation remains challenging. Here we show an electrochemical method for benzylic C–H hydroxylation using water as the oxygen source, in which overoxidation is suppressed by employing N-methyl-2-pyrrolidone as a co-solvent. The reaction proceeds without external oxidants, metal catalysts, or an inert atmosphere, using simple electrolytes. It is compatible with primary, secondary, and tertiary alkylarenes and exhibits good functional group tolerance. The method also enables isotope incorporation and is readily scalable, demonstrating practical synthetic utility. Mechanistic studies suggest that dual hydrogen-bonding interactions between the alcohol product and N-methyl-2-pyrrolidone may play a key role in suppressing overoxidation. Although the faradaic efficiency is moderate under the current conditions, this work provides a complementary strategy for selective benzylic C–H hydroxylation using water as a benign oxygen source. Overoxidation remains a selectivity challenge in direct benzylic C–H bond hydroxylation. Here, the authors present an electrochemical method using water as the hydroxyl source and N-methyl-2-pyrrolidone as a co-solvent, effectively suppressing overoxidation without external oxidants or metal catalysts.