Electrochemical [4+2] and [2+2] Cycloaddition for the Efficient Synthesis of Six- and Four-Membered Carbocycles

An efficient and sustainable electrochemical method for [4+2] and [2+2] cycloadditions has been developed, enabling the facile synthesis of six- and four-membered carbocycles. This metal-free strategy leverages constant-current electrolysis to generate key radical cation intermediates in situ from electron-rich olefins, eliminating the need for stoichiometric oxidants or transition-metal catalysts. The reaction demonstrates broad compatibility with various cyclopentadiene and styrene derivatives, constructing complex bicyclic frameworks with high efficiency and selectivity. Notably, the practicality of this protocol is demonstrated by its gram-scale implementation. A portion of the desired product could be isolated in good yield simply by filtration, avoiding the need for column chromatography. This work establishes electrosynthesis as a powerful and scalable alternative to conventional thermal and photochemical strategies, aligning with the principles of green chemistry.