Some aspects of the chemistry of benzobicyclo systems

The rearrangement reactions of 1-methoxybenzobicyclo-[2,2,2]-octatriene derivatives in strong acid have been studied. In particular 1-methoxytetrafluoro-, 1-methoxytetrachloro-, and 1-methoxybenzobarrelene have been prepared labelled with 14C at C-4. Rearrangement of these compounds, in strong acid, leads in each case, to three isomeric ketones. The major product in each rearrangement was the corresponding benzobarrelenone, formed, in each case, by two distinct pathways. The 14C label in each benzobarrelenone was scrambled between C-4 and C-5 as a result of the two different mechanisms. A suitable degradation procedure has been devised which allows the 14C activity in C-4 and C-5 of each ketone to be determined, and hence an evaluation of the percentage rearrangement which proceeds by the two mechanistic pathways previously suggested. [Continues.]