Acid catalyzed isomerization of bicyclic alkenes: a facile betweenanene synthesis

Isomerization of $\text{cis}$-bicyclo10.8.0]eicos-1(12)-ene ($\text{1a}$) and $\text{cis}$-bicyclo10.10.0]docos-1(12)-ene ($\text{1b}$) to 10.8]- and 10.10]betweenanene ($\text{2a}$ and $\text{2b}$) has been effected by sulfuric acid. In both cases, the betweenanene isomers were found to predominate at equilibrium (70/30 $\text{2a}$/$\text{1a}$ and 95/5> $\text{2b}$/$\text{1b}$).