In organic chemistry, annulation (; 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.
Transannulation
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)
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 Online Article See for example atranes.
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".
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