HOMOALLYLIC REARRANGEMENT OF BICYCLOBUTYLCARBINYL RADICALS

The free-radical additions of tetrachloromethane and bromotrichloromethane to a bicyclobutane-bridged enone (1) and diene (2) are reported. These reactions give in high yield products formed as result of a homoallylic rearrangement of the initially generated bicyclobutylcarbinyl radicals to vinylcyclopropyl radicals. The endo-halo-substituted cyclopropyl derivatives, obtained in the reaction of tetrachloromethane and diene (2) are thermally unstable and isomerize to benzyl derivatives, whereas the isomeric exo derivatives prove to be thermally stable. This difference in stability between endo• and exo-halo compounds is explained in terms of an electrocyclic, disrotatory opening of a cyclopropyl cation. © 1979, American Chemical Society. All rights reserved.