8.2.2 Halogen, Oxygen, Sulfur, and Nitrogen Migration

In the system X-C-C-Y, an atom X with an unshared pair of electrons can assist the heterolysis of the C-Y bond. In case of unsymmetrical system, nucleophilic attack predominates at the less substituted carbon of the bridged ion that leads to rearranged skeleton.

Some examples follow:

Rupe Rearrangement

The bridged cation may be produced via protonation of an unsaturated bond as in the Rupe rearrangement of a -acetylenic alcohols.