organic chemistry Organic chemistry is a subdiscipline within chemistry involving the 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.Clayden, J.; ...

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 of the ...

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

chemical reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the pos ...

in which a new ring 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 in 1935 as a method to create a six membered ring by forming three new carbon–carbon bonds. The method uses a keto ...

Danheiser annulation The Danheiser annulation or Danheiser TMS-cyclopentene annulation is an organic reaction of an α,β-unsaturated ketone and a trialkylsilylallene (e.g., trimethylsilyl- or triisopropylsilyl-) in the presence of a Lewis Acid to give a trialkylsil ...

and certain

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

s. 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

acene In organic chemistry, the acenes or polyacenes are a class of organic compounds and polycyclic aromatic hydrocarbons made up of benzene () rings which have been linearly fused. They follow the general molecular formula . The larger represent ...

s. 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 (all ...

molecule is created by intramolecular carbon-carbon bond formation in a large monocyclic ring. An example is the

samarium(II) iodide Samarium(II) iodide is an inorganic compound with the formula SmI2. When employed as a solution for organic synthesis, it is known as Kagan's reagent. SmI2 is a green solid and solutions are green as well. It is a strong one-electron reducing a ...

induced ketone -

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 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 ...

of ''5-methylenecyclooctanone'' which proceeds through a

ketyl A ketyl group in organic chemistry is an anion radical that contains a group R2C−O•. It is the product of the 1-electron reduction of a ketone. Another mesomeric structure has the radical position on carbon and the negative charge on oxyge ...

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 atoms, ...

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..html" ;"title="atrane.html" ;"title="Verkade base induces a transannular bonding, giving an atrane">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 ''Arkivoc'' (''Archive for Organic Chemistry'') is a peer-reviewed open access scientific journal covering all aspects of organic chemistry. It is published by the non-profit organization Arkat USA, which was established in 2000 through a personal ...

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 or bor ...

References

{{reflist Organic reactions Ring forming reactions