organic chemistry Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic matter, organic materials, i.e., matter in its various forms that contain ...

, annulation (; occasionally annelation) is a

chemical reaction A chemical reaction is a process that leads to the chemistry, chemical transformation of one set of chemical substances to another. When chemical reactions occur, the atoms are rearranged and the reaction is accompanied by an Gibbs free energy, ...

in which a new

ring (The) Ring(s) may refer to: * Ring (jewellery), a round band, usually made of metal, worn as ornamental jewelry * To make a sound with a bell, and the sound made by a bell Arts, entertainment, and media Film and TV * ''The Ring'' (franchise), a ...

is constructed on a molecule. : Examples are the

Robinson annulation The Robinson annulation is a chemical reaction used in organic chemistry for ring formation. It was discovered by Robert Robinson (organic chemist), Robert Robinson in 1935 as a method to create a six membered ring by forming three new carbon–c ...

, Danheiser annulation and certain

cycloaddition In organic chemistry, a cycloaddition is a chemical reaction in which "two or more Unsaturated hydrocarbon, unsaturated molecules (or parts of the same molecule) combine with the formation of a cyclic adduct in which there is a net reduction of th ...

s. Annular molecules are constructed from side-on condensed cyclic segments, for example

helicene In organic chemistry, helicenes are aromatic ortho substituent, ortho-condensed Polycyclic compound, polycyclic Aromaticity, aromatic compounds in which Benzene, benzene rings or other aromatics are angularly annulation, annulated to give helix, ...

s and acenes. In transannulation a

bicyclic A bicyclic molecule () is a molecule that features two joined rings. Bicyclic structures occur widely, for example in many biologically important molecules like α-thujene and camphor. A bicyclic compound can be carbocyclic (all of the ring ...

molecule is created by intramolecular carbon-carbon bond formation in a large monocyclic ring. An example is the samarium(II) iodide induced

ketone In organic chemistry, a ketone is an organic compound with the structure , where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group (a carbon-oxygen double bond C=O). The simplest ketone is acetone ( ...

alkene In organic chemistry, an alkene, or olefin, is a hydrocarbon containing a carbon–carbon double bond. The double bond may be internal or at the terminal position. Terminal alkenes are also known as Alpha-olefin, α-olefins. The Internationa ...

cyclization of ''5-methylenecyclooctanone'' which proceeds through a ketyl intermediate: :

Benzannulation

The term benzannulated compounds refers to derivatives of

cyclic compound A cyclic compound (or ring compound) is a term for a compound in the field of chemistry in which one or more series of atoms in the compound is connected to form a ring. Rings may vary in size from three to many atoms, and include examples where ...

s (usually aromatic) which are fused to a

benzene Benzene is an Organic compound, organic chemical compound with the Chemical formula#Molecular formula, molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar hexagonal Ring (chemistry), ring with one hyd ...

ring. Examples are listed in the table below: In contemporary chemical literature, the term benzannulation also means "construction of benzene rings from acyclic precursors". upright=1.4, Protonation of Verkade base induces a transannular bonding, giving an atrane.">atrane.html" ;"title="Verkade base induces a transannular bonding, giving an atrane">Verkade base induces a transannular bonding, giving an atrane.

Transannular interaction

A transannular interaction in chemistry is any chemical interaction (favorable or nonfavorable) between different chemical bond, non-bonding molecule, molecular functional group, 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.

References

{{reflist Ring forming reactions