Ring-Opening/Friedel–Crafts Cascade of Benzylcyclobutanones toward Naphthalenes

An unprecedented copper-catalyzed intramolecular ring-opening/Friedel-Crafts reaction of cyclobutanones is developed by judicious refinements of the substrate and reaction conditions. Distinct from previous reaction patterns, the in situ generated zwitterionic species from selective C-C bond cleavage of cyclobutanones was captured by properly installed benzyl units, delivering a variety of polysubstituted naphthalenes smoothly in up to 99% yield. The strategy is featured by the mild conditions without the employment of sensitive or stoichiometric Lewis acids, with water being the only byproduct. Besides 3-aryl cyclobutanones, 3-alkyl precursors were also proven to be compatible in the catalytic protocol. Synthesis and transformation of the reaction intermediate allowed for verification of the catalytic pathway.