Rationalizing the diverse reactivity of [1.1.1]propellane through σ–π-delocalization

and DFT calculations, we show that its reactions with anions and radicals are facilitated by increased delocalization of electron density over the propellane cage during addition, while reactions with cations involve charge transfer that relieves repulsion inside the cage. These results provide a unified framework to rationalize experimental observations of propellane reactivity, opening up opportunities for the exploration of new chemistry of [1.1.1]propellane and related strained systems that are useful building blocks in organic synthesis.