Rearrangement of radicals derived from bicyclo[5.1.0]octa-2,4-diene, tricyclo[6.1.0.0^2,4]nona-6-ene and tetracyclo[7.1.0.0^2,4.0^5,7]decane

ESR spectra from bicyclo[5.1.0]octadienyl and tricyclo[6.1.0.0^2,4]nona-6-enyl radicals, and from the rearrangement of tetracyclo[7.1.0.0^2,4.0^5,7]decanyl radicals have been observed. The rate of ring opening increases in the stated order. The ESR parameters and semiempirical calculations suggest that electron delocalisation into the three-membered rings is insignificant. At temperatures above ambient the bicyclo[5.1.0]octadienyl radical rearranges to the cycloheptatrienylmethyl radical, which in turn rearranges to the norcaradienylmethyl radical and hence to the vinylcyclohexadienyl radical, which gives styrene and products derived therefrom. 1,3- Bromination via the S_H2 reaction at the three-membered ring is also an important process for bicyclo[5.1.0]octa-2,4-diene.