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 materials, i.e., matter in its various forms that contain carbon atoms.Clay ...

annulation (from the

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power ...

''anellus'' for "little ring"; occasionally annelation) is a

chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and break ...

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

helicene In organic chemistry, helicenes are ortho-condensed polycyclic aromatic compounds in which benzene rings or other aromatics are angularly annulated to give helically-shaped chiral molecules. The chemistry of helicenes has attracted continuin ...

s and acenes. In transannulation a

bicyclic In chemistry, 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 (a ...

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 a functional group with the structure R–C(=O)–R', where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group –C(=O)– (which contains a carbon-oxygen double bon ...

alkene In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond. Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, an ...

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 chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen ato ...

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 an example the molecule

atrane Atranes are a class of tricyclic molecules with three five-membered rings. It is a heterocyclic structure similar to the propellanes. It has a transannular dative bond from a nitrogen at one bridgehead to a Lewis acidic atom such as silicon o ...

References

{{reflist Organic reactions Ring forming reactions