Annulation

Annulation (derived from annular, occasionally annelation) in organic chemistry is a chemical reaction in which a new ring is constructed on another molecule (often another ring). Examples are the Robinson 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) chloride induced ketone - alkene cyclization of 5-methylenecyclooctanone which proceeds through a ketyl intermediate :


 * [[Image:KetoneOlefinCyclization.png|400px|Ketone olefin cyclization]]