Electrochemically Driven Domino Nucleophilic Addition/Diels–Alder Reaction: From 2-Aminophenol Derivatives to Bridged Tricyclic Systems

The electrochemical methodology here reported allows the preparation of bridged tricyclic scaffolds through a rapid increase in the molecular complexity of simple and readily accessible starting materials. Standard conditions employing graphite as anode, nickel foam as cathode, and triflic acid as additive provided the target aza-caged structures in good yields. Alcohols proved to be the most efficient nucleophiles, affording the desired products in modest yields, while nitrogen-based nucleophiles generally resulted in decomposition, with the notable exception of 6-chloropurine, which gave the desired product in moderate yield. Plausibly, the process involves an anodic oxidative dearomatization that generates an o-quinone-type intermediate, which undergoes nucleophilic addition followed by an intramolecular Diels-Alder reaction. Cyclic voltammetry confirmed the aminophenol as the electroactive species, supporting the proposed mechanistic pathway.