Radical reactions of bicyclo[2.1.0]pentane

The photochemical reactions of bicyclo[2.1.0]pentane with bromine, bromotrichloromethane, t-butyl hypochlorite, di-t-butyl peroxide, and N-bromosuccinimide have been investigated. Trichloromethyl, t-butoxyl, and succinimidyl radicals abstract hydrogen from the C₄ ring. The expected bicyclopentyl radicals were not detected and if they are discrete intermediates they must rearrange by fission of the C(1)-C(4) bond common to the two rings to form cyclopent-3-enyl radicals. The e.s.r. spectrum of the latter radicals was obtained. Bromine (and chlorine) atoms may abstract hydrogen, but their major pathway involves attack at the bridgehead carbon atoms in an S _H2 reaction with fission of the C(1)-C(4) bond to give 3-halogenocyclopentyl radicals.