Synthesis of dibenzocycloketones by acyl radical cyclization from aromatic carboxylic acids using methylene blue as a photocatalyst

An efficient intramolecular radical cyclization reaction via photoredox catalysis was developed for the synthesis of dibenzocycloketone derivatives using methylene blue as a photosensitizer. This strategy could be widely used to synthesize large heterocycles due to the unique reactivity of phosphoranyl radicals formed by a polar/SET crossover between an aromatic carboxylic acid and a phosphine radical cation. Attractive features of this process include generation of an acyl radical by an inexpensive and metal-free photocatalyst, which effectively undergoes a cyclization process. An efficient intramolecular radical cyclization reaction via photoredox catalysis was developed for the synthesis of dibenzocycloketone derivatives using methylene blue as a photosensitizer.