Annulation

 ( Ring Forming Reactions ) 

In organic chemistry, annulation (; occasionally annelation) is a chemical reaction in which a new ring is constructed on a molecule.

[[Image:AnnulationStrategies.png|400px|Annulation:

A) intramolecular ring closing
B) transannulation
C) cycloaddition ]]

Examples are the Robinson annulation, Danheiser annulation and certain . Annular molecules are constructed from side-on condensed cyclic segments, for example and . 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)

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Benzannulation The term benzannulated compounds refers to derivatives of (usually aromatic) which are fused to a benzene ring. Examples are listed in the table below:

Pyrene
Quinoline	Pyridine
Isoquinoline
Chromene	Pyran
Isochromene
Indole	Pyrrole
Isoindole
Benzofuran	Furan
Isobenzofuran
Imidazole

In contemporary chemical literature, the term benzannulation also means "construction of benzene rings from acyclic precursors". induces a transannular bonding, giving an atrane.

(2025). 9780471936237 ISBN 9780471936237

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Transannular interaction A transannular interaction in chemistry is any chemical interaction (favorable or nonfavorable) between different chemical bond molecule functional group 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 Online Article See for example atrane.

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