Electron transfer reorganization of bicyclo[6.1.0]nonatriene and derivatives.

The radical cations of bicyclo[6.1.0]nonatriene (1a) and several derivatives (1b-1f) have been generated by photoinduced electron transfer in solution. The radical cation, 3a, derived from the parent has a weakened cyclopropane bond with spin (and charge) density at C sub 1 and C sub 8. Electron return in singlet pairs regenerates 1a. whereas triplet recombination gives rise to cyclononatetraene (6). Electron withdrawing substituents at C sub 9 (Cl, 1c) cause spin and charge to be restricted to the triene moiety. The 9,9-diphenyl derivative (1d) undergoes electron transfer induced rearrangement to 7- (beta, beta-diphenylethenyl)cycloheptatriene, whereas the spirofluorene derivative (1f) is converted to a barbaralane derivative (9f). The homoaromatic radical cation (10f) is suggested as an intermediate in this remarkable rearrangement.