Structures and names of common heterocyclic compoundsPyridine, a heterocyclic compound
Aheterocyclic compound orring structure is acyclic compound that has atoms of at least two differentelements as members of its ring(s).[1]Heterocyclic organic chemistry is the branch oforganic chemistry dealing with the synthesis, properties, and applications oforganic heterocycles.[2]
Examples of heterocyclic compounds include all of thenucleic acids, the majority of drugs, mostbiomass (cellulose and related materials), and many natural and synthetic dyes. More than half of known compounds are heterocycles.[3] 59% of USFDA-approved drugs containnitrogen heterocycles.[4]
The study of organic heterocyclic chemistry focuses especially on organic unsaturated derivatives, and the preponderance of work and applications involves unstrained organic 5- and 6-membered rings. Included arepyridine,thiophene,pyrrole, andfuran. Another large class of organic heterocycles refers to those fused tobenzene rings. For example, the fused benzene derivatives of pyridine, thiophene, pyrrole, and furan arequinoline,benzothiophene,indole, andbenzofuran, respectively. The fusion of two benzene rings gives rise to a third large family of organic compounds. Analogs of the previously mentioned heterocycles for this third family of compounds areacridine,dibenzothiophene,carbazole, anddibenzofuran, respectively.
Heterocyclic organic compounds can be usefully classified based on their electronic structure. The saturated organic heterocycles behave like the acyclic derivatives. Thus,piperidine andtetrahydrofuran are conventionalamines andethers, with modified steric profiles. Therefore, the study of organic heterocyclic chemistry focuses on organic unsaturated rings.
Some heterocycles contain no carbon. Examples areborazine (B3N3 ring),hexachlorophosphazenes (P3N3 rings), andtetrasulfur tetranitride S4N4. In comparison with organic heterocycles, which have numerous commercial applications, inorganic ring systems are mainly of theoretical interest.IUPAC recommends theHantzsch-Widman nomenclature for naming heterocyclic compounds.[5]
The 5-membered ring compounds containingtwo heteroatoms, at least one of which is nitrogen, are collectively called theazoles.Thiazoles andisothiazoles contain a sulfur and a nitrogen atom in the ring.Dithioles have two sulfur atoms.
A large group of 5-membered ring compounds withthree or more heteroatoms also exists. One example is the class ofdithiazoles, which contain two sulfur atoms and one nitrogen atom.
The 6-membered ring compounds containingtwo heteroatoms, at least one of which is nitrogen, are collectively called theazines.Thiazines contain a sulfur and a nitrogen atom in the ring.Dithiines have two sulfur atoms.
Six-membered rings with six heteroatoms Thehypothetical chemical compound with six nitrogen heteroatoms would behexazine.Borazine is a six-membered ring with three nitrogen heteroatoms and three boron heteroatoms.
In a 7-membered ring, the heteroatom must be able to provide an empty π-orbital (e.g. boron) for "normal" aromatic stabilization to be available; otherwise,homoaromaticity may be possible.
Heterocyclic rings systems that are formally derived by fusion with other rings, eithercarbocyclic or heterocyclic, have a variety of common and systematic names. For example, with the benzo-fused unsaturated nitrogen heterocycles, pyrrole providesindole orisoindole depending on the orientation. The pyridine analog isquinoline orisoquinoline, and the class of analogues with two nitrogen atoms is known as thebenzodiazines. For azepine,benzazepine is the preferred name. Likewise, the compounds with two benzene rings fused to the central heterocycle arecarbazole,acridine, and dibenzoazepine.Thienothiophene are the fusion of two thiophene rings.Phosphaphenalenes are a tricyclic phosphorus-containing heterocyclic system derived from the carbocyclephenalene.
^Rees, Charles W. (1992). "Polysulfur-Nitrogen Heterocyclic Chemistry".Journal of Heterocyclic Chemistry.29 (3):639–651.doi:10.1002/jhet.5570290306.
^Edon Vitaku, David T. Smith, Jon T. Njardarson (2014). "Analysis of the Structural Diversity, Substitution Patterns, and Frequency of Nitrogen Heterocycles among U.S. FDA Approved Pharmaceuticals".J. Med. Chem.57 (24):10257–10274.doi:10.1021/jm501100b.PMID25255204.{{cite journal}}: CS1 maint: multiple names: authors list (link)
.svg)
