Electron transfer reactions of bicyclo[4.2.1.]nonatrienes: Formation of a Bishomoheptafulvene radical cation.

The radical cation (3+) of 9-methylenebicyclo[4.2.1]nona- 2,4,7- triene undergoes rapid intramolecular cyclization to generate an isomeric radical cation (15+) derived from a tetracyclic structure. In contrast, the hydrocation 15 suffers retrocyclization to regenerate 3. The comparative stability of 15+ is ascribed to its bishomoaromatic character. Four radical cations of less unsaturated model compounds support the assigned structure.