Electrochemical Synthesis of Spirodienones with Sequential Ring Expansion to Fused 6–7–6 Tricycles

An intramolecular electro-oxidative spirocyclization of tethered arenes is developed to access spirodienones under metal- and chemical-oxidant-free conditions. This method exhibits good functional group tolerance, allowing a broad spectrum of substrates with yields of up to 85% and scalability to 5 mmol. Mechanistic studies suggested selective oxidation of the anisole moiety followed by 6-exo-trig spirocyclization. A sequential ring-expansion protocol was also established to convert the synthesized spiro compounds into fused 6–7–6 tricyclic derivatives.