Pericyclic Reactions: Further Examples
Pericyclic Reactions: Coarctate Reactions
Coarctate reactions are related to pericyclic reactions.
By definition, pericyclic reactions are characterized by cyclic, aromatic transition states and bond cleavage and formation take place simultaneously in a cyclic mechanism. In coarctate reactions formation and cleavage do not follow a cyclic pathway. Contrary to pericyclic reactions they contain at least one atom at which two bonds are broken and two are formed formed simultaneously. Examples:
The topology of the overlapping participating orbitals resembles a constricted cycle giving rise to the name coarctate (Latin coarctare=to constrict).
Formally, the epoxidation of alkenes with peracids can also be considered a coarctate reaction. In this case it is the transferred oxygen atom at which two bonds are simultaneously formed (C-O bond in the epoxide) and broken (H-O and O-O bonds in the peracid)