Annulation (derived from
annular, occasionally annelation) in organic chemistryis a chemical reactionin which a new ring is constructed on another molecule (often another ring). [GoldBookRef|title=annulation|url=http://goldbook.iupac.org/A00367.html GoldBookRef|title=annelation|url=http://goldbook.iupac.org/A00365.html]
Examples are the
Robinson annulationand certain cycloadditions. Annular molecules are constructed from side-on condensed cyclic segments, for example helicenes and acenes. In transannulation a bicyclicmolecule is created by intramolecular carbon-carbon bondformation in a large monocyclic ring. An example is the samarium(II) chlorideinduced ketone- alkene cyclizationof "5-methylenecyclooctanone" which proceeds through a ketylintermediate ["Construction of Bicyclic Ring Systems via a Transannular SmI2-Mediated Ketone-Olefin Cyclization Strategy"Gary A. Molander, Barbara Czakó, and Michael Rheam J. Org. Chem.; 2007; 72(5) pp 1755 - 1764; (Article) DOI|10.1021/jo062292d] :
The term benzannulated compounds refers to derivatives of
cyclic compounds (usually aromatic) which are fused to a benzenering. Examples are listed in the table below:
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