Abstract
The bromination of bicyclo[2.2.2]octadiene‐(2,5) (1) leads to a mixture of trans‐2,3‐dibromo‐bicyclo[2.2.2]octene‐(5) (9) and trans‐3,5‐dibromo‐homotricyclene (7a) in the ratio 7:3. This result is explained by endo addition of bromine to (1) with formation of an intermediate homoallylic ion (23) or, possibly, the unusual symmetrical bridged bromonium ion (24).