Annulation in organic chemistry

Organic chemistry

Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, composition, reactions, and preparation of carbon-based compounds, hydrocarbons, and their derivatives...

 is a chemical reaction

Chemical reaction

A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity...

 in which a new ring is constructed on another molecule (often another ring).

Examples are the Robinson annulation

Robinson annulation

The Robinson annulation is an organic reaction used to create a six-member ring α,β-unsaturated cyclic ketone, using a ketone and methyl vinyl ketone...

, Danheiser annulation

Danheiser Annulation

The Danheiser annulation or Danheiser TMS-cyclopentene annulation is an organic reaction of an α,β-unsaturated ketone and a trialkylsilylallene in the presence of a Lewis Acid to give a trialkylsilylcyclopentene in a regiocontrolled annulation....

 and certain cycloaddition

Cycloaddition

A cycloaddition is a pericyclic chemical reaction, in which "two or more unsaturated molecules combine with the formation of a cyclic adduct in which there is a net reduction of the bond multiplicity." The resulting reaction is a cyclization reaction.Cycloadditions are usually described by the...

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

Helicene

Helicenes in organic chemistry are ortho-condensed polycyclic aromatic compounds in which benzene rings or other aromatics are angularly annulated to give helically-shaped molecules...

s and acene

Acene

Acenes or polyacenes is a class of organic compounds and polycyclic aromatic hydrocarbons made up of linearly fused benzene rings. The larger representatives have potential interest in optoelectronic applications and are actively researched in chemistry and electrical engineering...

s. In transannulation a bicyclic molecule is created by intramolecular

Intramolecular

Intramolecular in chemistry describes a process or characteristic limited within the structure of a single molecule, a property or phenomenon limited to the extent of a single molecule.- Examples :...

 carbon-carbon bond

Carbon-carbon bond

A carbon–carbon bond is a covalent bond between two carbon atoms. The most common form is the single bond: a bond composed of two electrons, one from each of the two atoms. The carbon–carbon single bond is a sigma bond and is said to be formed between one hybridized orbital from each...

 formation in a large monocyclic ring. An example is the samarium(II) iodide

Samarium(II) iodide

Samarium iodide is a green solid composed of samarium and iodine, with a melting point of 520 °C where the samarium atom has a coordination number of seven in a capped octahedral configuration...

 induced ketone

Ketone

In organic chemistry, a ketone is an organic compound with the structure RCR', where R and R' can be a variety of atoms and groups of atoms. It features a carbonyl group bonded to two other carbon atoms. Many ketones are known and many are of great importance in industry and in biology...

 - alkene

Alkene

In organic chemistry, an alkene, olefin, or olefine is an unsaturated chemical compound containing at least one carbon-to-carbon double bond...

 cyclization of 5-methylenecyclooctanone which proceeds through a ketyl

Ketyl

A ketyl group in organic chemistry is an anion radical with the general structure C-O. in which an oxygen radical is bonded directly to carbon. This radical is very unstable and appears in chemical reactions as a reactive intermediate...

 intermediate :

Benzannulation

The term benzannulated compounds refers to derivatives of cyclic compound

Cyclic compound

In chemistry, a cyclic compound is a compound in which a series of atoms is connected to form a loop or ring.While the vast majority of cyclic compounds are organic, a few inorganic substances form cyclic compounds as well, including sulfur, silanes, phosphanes, phosphoric acid, and triboric acid. ...

s (usually aromatic) which are fused to a benzene

Benzene

Benzene is an organic chemical compound. It is composed of 6 carbon atoms in a ring, with 1 hydrogen atom attached to each carbon atom, with the molecular formula C6H6....

 ring. Examples are listed in the table below:

Benzannulated derivative	Source of cyclic compound
Benzopyrene Benzopyrene Benzo[a]pyrene, C20H12, is a five-ring polycyclic aromatic hydrocarbon whose metabolites are mutagenic and highly carcinogenic. Benzo[a]pyrene is listed as a Group 1 carcinogen by the IARC. It belongs to a class of polycyclic aromatic compounds known as benzopyrenes, which consist of a benzene...	Pyrene Pyrene Pyrene is a polycyclic aromatic hydrocarbon consisting of four fused benzene rings, resulting in a flat aromatic system. The chemical formula is . This colourless solid is the smallest peri-fused PAH...
Quinoline Quinoline Quinoline is a heterocyclic aromatic organic compound. It has the formula C9H7N and is a colourless hygroscopic liquid with a strong odour. Aged samples, if exposed to light, become yellow and later brown...	Pyridine Pyridine Pyridine is a basic heterocyclic organic compound with the chemical formula C5H5N. It is structurally related to benzene, with one C-H group replaced by a nitrogen atom...
Isoquinoline Isoquinoline Isoquinoline is a heterocyclic aromatic organic compound. It is a structural isomer of quinoline. Isoquinoline and quinoline are benzopyridines, which are composed of a benzene ring fused to a pyridine ring. In a broader sense, the term isoquinoline is used to make reference to isoquinoline...
Chromene	Pyran Pyran In chemistry, a pyran, or oxine, is a six-membered heterocyclic, non-aromatic ring, consisting of five carbon atoms and one oxygen atom and containing two double bonds. The molecular formula is C5H6O. There are two isomers of pyran that differ by the location of the double bonds...
Isochromene
Indole Indole Indole is an aromatic heterocyclic organic compound. It has a bicyclic structure, consisting of a six-membered benzene ring fused to a five-membered nitrogen-containing pyrrole ring. Indole is a popular component of fragrances and the precursor to many pharmaceuticals. Compounds that contain an...	Pyrrole Pyrrole Pyrrole is a heterocyclic aromatic organic compound, a five-membered ring with the formula C4H4NH. It is a colourless volatile liquid that darkens readily upon exposure to air. Substituted derivatives are also called pyrroles, e.g., N-methylpyrrole, C4H4NCH3...
Isoindole Isoindole Isoindole in heterocyclic chemistry is a benzo fused pyrrole. The compound is an isomer of indole and its reduced form is an isoindoline.In solution its tautomer without full aromaticity over the whole ring system is predominant:...
Benzofuran Benzofuran Benzofuran is the heterocyclic compound consisting of fused benzene and furan rings. This colourless liquid is a component of coal tar. Benzofuran is the "parent" of many related compounds with more complex structures. For example, psoralen is a benzofuran derivative that occurs in several...	Furan Furan Furan is a heterocyclic organic compound, consisting of a five-membered aromatic ring with four carbon atoms and one oxygen. The class of compounds containing such rings are also referred to as furans....
Isobenzofuran Isobenzofuran Isobenzofuran is a heterocyclic compound consisting of fused benzene and furan rings. It is isomeric with benzofuran.Isobenzofuran is highly reactive and rapidly polymerizes; however, it has been identified and prepared by thermolysis of suitable precursors and trapped at low temperature.Though...
Benzimidazole Benzimidazole Benzimidazole is a heterocyclic aromatic organic compound. This bicyclic compound consists of the fusion of benzene and imidazole. The most prominent benzimidazole compound in nature is N-ribosyl-dimethylbenzimidazole, which serves as an axial ligand for cobalt in vitamin B12. Benzimidazole, in...	Imidazole Imidazole Imidazole is an organic compound with the formula C3H4N2. This aromatic heterocyclic is a diazole and is classified as an alkaloid. Imidazole refers to the parent compound, whereas imidazoles are a class of heterocycles with similar ring structure, but varying substituents...

Transannular interaction

A transannular interaction in chemistry

Chemistry

Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....

 is any chemical interaction (favorable or nonfavorable) between different non-bonding

Chemical bond

A chemical bond is an attraction between atoms that allows the formation of chemical substances that contain two or more atoms. The bond is caused by the electromagnetic force attraction between opposite charges, either between electrons and nuclei, or as the result of a dipole attraction...

 molecular

Molecule

A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...

 groups

Functional group

In organic chemistry, functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. The same functional group will undergo the same or similar chemical reaction regardless of the size of the molecule it is a part of...

 in a large ring or macrocycle

Macrocycle

A macrocycle is, as defined by IUPAC, "a cyclic macromolecule or a macromolecular cyclic portion of a molecule." In the chemical literature, organic chemists may consider any molecule containing a ring of nine or more atoms to be a macrocycle...

 . See for an example the molecule atrane

Atrane

An Atrane is a tricyclic molecule with three five-membered rings. It has a transannular dative bond by a nitrogen atom, depicted as A. The name "atrane" was first proposed by Mikhail Grigorievich Voronkov....

.