Electrochemical Control of Scholl Reaction: Arenium Cation Versus Radical Cation Pathways

The Scholl reaction is a cornerstone method for constructing polycyclic aromatic hydrocarbons, yet its mechanism remains highly debated because arenium and radical cation intermediates are difficult to characterize. Herein, we demonstrate that electrochemical oxidation provides precise mechanistic control: a low-potential acidic (LPA) condition selectively favors the arenium cation pathway, whereas a high-potential neutral (HPN) condition promotes the radical cation pathway. While it is often assumed that only one mechanism operates under a given set of chemical oxidation conditions, our results reveal that most substrates can react via both pathways. Dialkoxyphenyl groups are found to facilitate the radical cation pathway, although no general correlation with overall substrate electron richness is observed. This electrochemical control provides the experimental basis to re-evaluate previously proposed mechanisms for certain substrates. We demonstrate that switching between LPA and HPN conditions yields different products from the same 3,3'-diphenyl-2,2'-binaphthalene substrate, thereby correcting the computational assignment of the corresponding pathways. Additionally, we show that a tetracene-derived substrate undergoes cyclodehydrogenation through the arenium cation pathway, revising the computationally assigned dication mechanism for this transformation. Collectively, these results establish electrochemistry as a powerful alternative to traditional chemical oxidation, offering unprecedented experimental control to resolve fundamental mechanistic debates about the Scholl reaction.