Annulation

Annulation: A intramolecular ring closing B transannulation C cycloadditionAnnulation: A intramolecular ring closing B transannulation C cycloaddition

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).[1] 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 [2]:

Ketone olefin cyclization

## References

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1. ↑ Template:GoldBookRef Template:GoldBookRef
2. ↑ 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