According to a systematic classification of about 80000 reactions, most organic reactions can be described by a linear (i.e. nucleophilic / electrophilic attack, substitution, elimnination) or cyclic (pericyclic reactions) sequence of electron pushing arrows. However, there is a third class of reactions that we coined "coarctate reations". Coarctate mechanisms include at least one atom (or a sequence of atoms) at which two bonds are made and two bonds are broken simultaneously. A prominent example is the epoxidation of alkenes with peroxocarboxylic acids.
Because of their intricate mechanisms, coarctate reactions are less exhaustively investigated than pericyclic or linear reactions. Based on their common reaction principle, we predicted a number of new reactions which have been realized in the laboratory. Among them are particularly useful synthetic methods such as coarctate cyclizations.
Coarctate transition states: the discovery of a reaction principle.
J. Chem. Inf. Comput. Sci. 1994, 34, 91-102.