annulation
{{short description|Chemical reaction constructing a new ring on a molecule}}
{{distinguish|Annulment}}
In organic chemistry, annulation ({{ety|la|anellus|little ring}}; occasionally annelation) is a chemical reaction in which a new ring is constructed on a molecule.{{GoldBookRef|title=annulation|file=A00367 }}{{GoldBookRef|title=annelation|file=A00365 }}
:[[Image:AnnulationStrategies.png|400px|Annulation:
A) intramolecular ring closing
B) transannulation
]]
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: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}}
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:
| class="wikitable" style="text-align:center"
! Benzannulated derivative !! Source of cyclic compound | |
| Benzopyrene | Pyrene |
| Quinoline
|rowspan=2| Pyridine | |
| Isoquinoline | |
| Chromene
|rowspan=2| Pyran | |
| Isochromene | |
| Indole
|rowspan=2| Pyrrole | |
| Isoindole | |
| Benzofuran
|rowspan=2| Furan | |
| Isobenzofuran | |
| Benzimidazole | Imidazole |
In contemporary chemical literature, the term benzannulation also means "construction of benzene rings from acyclic precursors".{{Cite journal |last1=Swami |first1=Bhawna |last2=Yadav |first2=Deepak |last3=Menon |first3=Rajeev S. |date=January 2022 |title=Benzannulation Reactions: A Case for Perspective Change From Arene Decoration to Arene Construction |url=https://onlinelibrary.wiley.com/doi/10.1002/tcr.202100249 |journal=The Chemical Record |language=en |volume=22 |issue=1 |pages=e202100249 |doi=10.1002/tcr.202100249 |pmid=34796605 |s2cid=244403005 |issn=1527-8999|url-access=subscription }}image:VerkadeProtn.svg induces a transannular bonding, giving an atrane.{{cite book|doi=10.1002/047084289X.rn00702.pub2|chapter=Proazaphosphatrane|title=Encyclopedia of Reagents for Organic Synthesis|year=2012|last1=Verkade|first1=John G.|last2=Urgaonkar|first2=Sameer|isbn=978-0471936237}}]]
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.
Experimental evidence in support of transannular interactions in diketones Kata Mlinaric-Majerski, Marijana Vinkovic, Danko Škare, Alan P. Marchand Arkivoc DS-339E 2002 [http://www.arkat-usa.org/ark/journal/2002/I04_Sunko/DS-339E/339E.asp Online Article] {{Webarchive|url=https://web.archive.org/web/20060504182220/http://www.arkat-usa.org/ark/journal/2002/I04_Sunko/DS-339E/339E.asp |date=2006-05-04 }} See for example atranes.
References
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