Annulation
In organic chemistry annulation is a chemical reaction in which a new ring is constructed on a molecule.
Examples are the Robinson annulation, Danheiser annulation and certain cycloadditions. Annular molecules are constructed from side-on condensed cyclic segments, for example helicenes and acenes. In transannulation a bicyclic molecule is created by intramolecular carbon-carbon bond formation in a large monocyclic ring. An example is the samarium iodide induced ketone - alkene cyclization of 5-methylenecyclooctanone which proceeds through a ketyl intermediate:
Benzannulation
The term benzannulated compounds refers to derivatives of cyclic compounds which are fused to a benzene ring. Examples are listed in the table below:| Benzannulated derivative | Source of cyclic compound |
| Benzopyrene | Pyrene |
| Quinoline | Pyridine |
| Isoquinoline | Pyridine |
| Chromene | Pyran |
| Isochromene | Pyran |
| Indole | Pyrrole |
| Isoindole | Pyrrole |
| Benzofuran | Furan |
| Isobenzofuran | Furan |
| Benzimidazole | Imidazole |
induces a transannular bonding, giving an atrane.