Annulation

Short description: Chemical reaction constructing a new ring on a molecule

In organic chemistry, annulation (from la anellus 'little ring'; occasionally annelation) is a chemical reaction in which a new ring is constructed on a molecule.[1]

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(II) iodide induced ketone \- alkene cyclization of 5-methylenecyclooctanone which proceeds through a ketyl intermediate:[2]

## Benzannulation

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".[3]thumb|upright=1.4|Protonation of [[Verkade base induces a transannular bonding, giving an atrane.[4]]]

## Transannular 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.[5] See for example atranes.

## References

1. ↑ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version:  (2006-) "annulation". doi:10.1351/goldbook.A00367IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version:  (2006-) "annelation". doi:10.1351/goldbook.A00365.html
2. ↑ Construction of Bicyclic Ring Systems via a Transannular SmI2-Mediated Ketone-Olefin Cyclization StrategyGary A. Molander, Barbara Czakó, and Michael Rheam J. Org. Chem.; 2007; 72(5) pp 1755 - 1764; (Article) doi:10.1021/jo062292d
3. ↑ Swami, Bhawna; Yadav, Deepak; Menon, Rajeev S. (January 2022). "Benzannulation Reactions: A Case for Perspective Change From Arene Decoration to Arene Construction" (in en). The Chemical Record 22 (1): e202100249. doi:10.1002/tcr.202100249. ISSN 1527-8999. PMID 34796605. https://onlinelibrary.wiley.com/doi/10.1002/tcr.202100249.
4. ↑ Verkade, John G.; Urgaonkar, Sameer; Verkade, John G.; Urgaonkar, Sameer (2012). "Proazaphosphatrane". Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rn00702.pub2. ISBN 978-0471936237.
5. ↑ Experimental evidence in support of transannular interactions in diketones Kata Mlinaric-Majerski, Marijana Vinkovic, Danko Škare, Alan P. Marchand Arkivoc DS-339E 2002 Online Article

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