The Bicycle Rearrangement; A Review of an Unusual Photochemical Reaction

Abstract

The bicycle rearrangement is an intriguing reaction in which a divalent carbon, bearing two substituents and bound to a π-system with two sp⁵ orbitals, moves along the molecule as if the two sp⁵ orbitals were bicycle wheels and the two groups were “handlebars.” The rearrangement may be envisaged as involving conversion of one cyclopropyldicarbinyl moiety into another such system.
The rearrangement occurs in a variety of molecular environments. For example, the mechanism of the well-known 2,5-cyclohexadienone rearrangement involves a bicycle step. Also the Di-π-Methane rearrangement has a bicycle step in its mechanism. Additionally, a variety of vinylcyclopropanes with appropriate substitution undergo bicycle rearrangements. These reactions are stereospecific with the groups on the migrating carbon (i.e. the “handlebars”) maintaining their stereochemical integrity.