Barrelene–semibullvalene rearrangement induced by visible light: synthesis of dicorannulenosemibullvalene dimethyl dicarboxylate

A clean, quick conversion of biscorrannulenobarrelene dicarboxylate to the respective semibullvalene is observed upon irradiation of solutions of the former with a sun lamp. This represents the first reported example of such rearrangement induced by visible light. Hybrid density functional theory calculations predict the exo–endo conformer of the semibullvalene as the most stable, with the bis-exo and bis-endo conformers being higher in energy by ca. 1 and 4 kcal/mol, respectively.