Construction of a hemifullerene skeleton: a regioselective intramolecular oxidative cyclization.

A two-step synthesis of a strained π bowl, with hemifullerene skeleton from sumanene, was achieved in a high yield. The first step is a base-promoted condensation reaction with a benzophenone compound, bis(3,5-dimethylphenyl)methanone. The second step is the regioselective intramolecular oxidative cyclization, which is a key reaction for the hemifullerene skeleton synthesis. This regioselective cyclization is likely to be under thermodynamic control. This strategy will allow facile synthesis of various highly strained π bowls.