Pyridyne in

chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds made of atoms, molecules and ions ...

is the

pyridine Pyridine is a basic heterocyclic organic compound with the chemical formula . It is structurally related to benzene, with one methine group replaced by a nitrogen atom. It is a highly flammable, weakly alkaline, water-miscible liquid with a d ...

analogue of benzyne. Pyridynes are the class of

reactive intermediate In chemistry, a reactive intermediate or an intermediate is a short-lived, high-energy, highly reactive molecule. When generated in a chemical reaction, it will quickly convert into a more stable molecule. Only in exceptional cases can these comp ...

s derived from pyridine. Two isomers exist, the 2,3-pyridine (2,3-didehydropyridine) and the 3,4-pyridyne (3,4-didehydropyridine). The reaction of 3-bromo-4-chloropyridine with

furan Furan is a heterocyclic organic compound, consisting of a five-membered aromatic ring with four carbon atoms and one oxygen atom. Chemical compounds containing such rings are also referred to as furans. Furan is a colorless, flammable, highly ...

and lithium amalgam gives 1,4-epoxy-dihydroquinoline through the 2,3-pyridyne intermediate. The reaction of 4-bromopyridine with

sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable iso ...

in liquid

ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous was ...

gives both

3-aminopyridine 3-Aminopyridine is an aminopyridine. It is a colorless solid. Preparation 3-Aminopyridine is prepared by heating nicotinamide with sodium hypobromite which is in turn prepared ''in situ'' by the reaction of sodium hydroxide and bromine at 70& ...

and 4-aminopyridine through the 3,4-pyridyne intermediate and an

E1cB-elimination reaction The E1cB elimination reaction is a type of elimination reaction which occurs under basic conditions, where the hydrogen to be removed is relatively acidic, while the leaving group (such as -OH or -OR) is a relatively poor one. Usually a moderate t ...

History

Pyridynes were first postulated by Levine and Leake in 1955. In 1969 Zoltewicz and Nisi trapped 3,4-pyridyne in a reaction of 3-bromopyridine with

methylmercaptan Methanethiol (also known as methyl mercaptan) is an organosulfur compound with the chemical formula . It is a colorless gas with a distinctive putrid smell. It is a natural substance found in the blood, brain and feces of animals (including humans ...

and

sodium amide Sodium amide, commonly called sodamide (systematic name sodium azanide), is the inorganic compound with the formula . It is a salt composed of the sodium cation and the azanide anion. This solid, which is dangerously reactive toward water, is whit ...

in ammonia. The methylthio and amino pyridines were found to be formed in the same ratio. : Pyridyne intermediate

In 1972 Kramer and Berry inferred the formation of 3,4-pyridyne in gas-phase photolysis of pyridine-3-diazonium-4-carboxylate via

time-of-flight mass spectrometry Time-of-flight mass spectrometry (TOFMS) is a method of mass spectrometry in which an ion's mass-to-charge ratio is determined by a time of flight measurement. Ions are accelerated by an electric field of known strength. This acceleration result ...

. The dimer compound diazabiphenylene was detected. In 1988 Nam and Leroy reported the

matrix isolation Matrix isolation is an experimental technique used in chemistry and physics. It generally involves a material being trapped within an unreactive matrix. A ''host'' matrix is a continuous solid phase in which ''guest'' particles (atoms, molecules, i ...

(13K, Ar) of 3,4-pyridyne by

photolysis Photodissociation, photolysis, photodecomposition, or photofragmentation is a chemical reaction in which molecules of a chemical compound are broken down by photons. It is defined as the interaction of one or more photons with one target molecule. ...

of 3,4-pyridinedicarboxylic anhydride with the IR-spectrum revealing an acetylenic bond in the same way as ortho-benzyne.

Scope

Strategies involving pyridynes have been employed in the

total syntheses Total synthesis is the complete chemical synthesis of a complex molecule, often a natural product, from simple, commercially-available precursors. It usually refers to a process not involving the aid of biological processes, which distinguishes ...

ellipticine Ellipticine is an alkaloid first extracted from trees of the species '' Ochrosia elliptica'' and ''Rauvolfia sandwicensis'', which inhibits the enzyme topoisomerase II via intercalative binding to DNA. Natural occurrence and synthe ...

and (S)-Macrostomine.''A Five-Step Synthesis of (S)-Macrostomine from (S)-Nicotine'' Monica F. Enamorado, Pauline W. Ondachi, and Daniel L. Comins Organic Letters 2010 12 (20), 4513-4515

References

{{reflist Reactive intermediates