AbstractWhen subjected to pyrolysis inpara‐di‐isopropylbenzene (270°C, 40h) [2.2.2] (1,2,4)cyclophane (5) is cleaved to 2,9‐dimethyldibenzo[a,e]cyclooctadiene (8). Under comparable conditions (290°C, 65h), [2.2.2.2] (1,2,3,5)cyclophane (6) is converted to 6,11‐dimethyl[2.2.2] (1,2,3)cyclophane (9), the first derivative of a symmetrical [2n]cyclophane carrying three consecutive ethano bridges. The isomeric [2.2.2.2]‐ (1,2,3,4)cyclophane (7), on the other hand, cannot be induced to undergo carbon‐carbon‐bond cleavage followed by hydrogen abstraction. Under the influence of aluminiumtrichloride/hydrogenchloride hydrocarbon5isomerizes to the unsymmetrical [2.2.2] (1,2,4) (1,2,5)cyclophane (10), whereas6and7are stable under these conditions. The thermal stability and propensity of multiply‐bridged cyclophanes to undergo isomerization react