Annulation
Chemical reaction constructing a new ring on a molecule
In organic chemistry, annulation (from Latin anellus 'little ring'; occasionally annelation) 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.
01Transannulation
In transannulation a bicyclic molecule is created by intramolecular carbon-carbon bond formation in a large monocyclic ring. An example is the samarium(II) iodide induced ketone - alkene cyclization of 5-methylenecyclooctanone which proceeds through a ketyl intermediate:
02Transannular interaction
A transannular interaction in chemistry is any chemical interaction (favorable or nonfavorable) between different non-bonding molecular groups in a large ring or macrocycle. See for example atranes.
03Benzannulation
The term benzannulated compounds refers to derivatives of cyclic compounds (usually aromatic) 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 | |
| Chromene | Pyran |
| Isochromene | |
| Indole | Pyrrole |
| Isoindole | |
| Benzofuran | Furan |
| Isobenzofuran | |
| Benzimidazole | Imidazole |
In contemporary chemical literature, the term benzannulation also means "construction of benzene rings from acyclic precursors".
Sources and credits
This article is adapted from the Wikipedia article “Annulation”, written by its contributors and licensed under CC BY-SA 4.0. Fathomly has changed the layout, removed citation markers, navigation and maintenance notices, and adjusted punctuation. This adapted version is shared under the same license. For references, see the original article.
Images, from Wikimedia Commons:
- AnnulationStrategies.png by en:User:V8rik, CC BY-SA 3.0
- KetoneOlefinCyclization.png by V8rik, CC BY-SA 3.0
- VerkadeProtn.svg by Smokefoot, Public domain
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