[1.1.1]Propellane shows an equivalent effect, where delocalization now extends across all three bridging methylene groups and the bridgehead carbon atoms. -30 It is interesting to note that while the interbridgehead bond in [1.1.1]propellane can be described as a charge-shift bond, the origins of its reactivity are thus no different to those of the covalent bonds of, for instance, cyclopropane; it is simply the combination of the strain release driving force and the ability to delocalize electrons over an additional two methylene groups that explains the reactivity differences.