Summary Hole formation (ionization) is predicted to accelerate a variety of pericyclic reactions, especially those in which highly nonsynchronous transition states are readily accessible. The cation-radical Diels-Alder reaction path is characterized as concerted and highly nonsynchronous. The reaction path for the [2+ 11 cycloaddition emerges as a two- step sequence. An intermediate long-bond cyclobutane cation radical is formed via a ...