Ene reactions are Group transfer reactions between an alkyne or alkene, or similar double bonded species and an allyl-like species. These reactions typically require highly activated substrates and high temperatures. They are also often found as unintended byproducts of chemical reactions. Group transfer reactions are pericyclic reactions where one pi bond is converted to one sigma bond , at the same time that a sigma bond migrates. ... Alkynes are hydrocarbons that have at least one triple bond between two carbon atoms. ... An alkene is an unsaturated hydrocarbon containing at least one carbon-carbon double bond. ... Covalent bonding is a form of chemical bonding characterized by the sharing of one or more pairs of electrons between atoms, in order to produce a mutual attraction, which holds the resultant molecule together. ... An allyl group is an alkene hydrocarbon group with the formula H2C=CH-CH2-. It is made up of a vinyl group, CH2=CH-, attached to a methylene -CH2. ...

The general scheme for the ene reaction. ...

The convention for describing an ene reaction is to describe it as a reaction between an ene and an enophile. This can be confusing, since the enophile is very often itself an alkene. The ene is always an allyl group with a labile allylic hydrogen which participates in the reaction as shown above. For most known ene reactions, the ene is electron-rich, and the enophile is electron-deficient. Unlike the Diels-Alder reaction, only a handful of exotic inverse-electron demand ene reactions (electron-deficient ene, electron-rich eneophile) are known. The Diels-Alder reaction is an organic chemical reaction (specifically, a cycloaddition) between a conjugated diene and a substituted alkene, commonly termed the dienophile to form a substituted cyclohexene system. ...

The most well known ene reactions are the singlet oxygen ene reaction with singlet oxygen (X = Y = oxygen; Z = carbon), and the Conia ene reaction (X = Y = carbon , Z = oxygen) which is followed by tautomerization to regenerate the ketone. Selenium dioxide oxidation is also an ene reaction coupled to a retro-[3 + 2] reaction. Singlet Singlet oxygen is a reactive oxygen species that is higher in energy than the predominant species in the atmosphere, triplet oxygen. ... Tautomers are organic compounds that are interconvertible by a chemical reaction called tautomerization. ...

Maleic anhydride is known to participate in many ene reactions; this is due to the combined electron-widthdrawing power of the two carbonyl groups pendant to the alkene. An example is given below. ^[1]. In chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom. ...

Much like with Diels-Alder reactions, Lewis acids such as boron trifluoride or aluminium chloride can participate in metal-catalyzed ene reactions. These reactions are still pericyclic as they operate by generating the reactive complex which still undergoes a concerted reaction, as opposed to intercepting the cyclic transition state as an intermediate. Image File history File links Allyl_benzene_ene_reaction. ... In chemistry, a Lewis acid is any acid that can accept a pair of electrons and form a coordinate covalent bond, after the American chemist Gilbert Lewis. ... Boron trifluoride (BF3, trifluoroborane) is a pungent colourless toxic gas. ... Aluminium chloride (AlCl3) is a compound of aluminium and chlorine. ...

In an example, Citronellal gives an intramolecular ring-closure with niobium pentachloride as Lewis acid catalyst. ^[2] in the carbonyl-ene reaction (X = Z = carbon; Y = oxygen), where a carbonyl group is the enophile. Citronellal or rhodinal or 3,7-dimethyl-6-octen-1-al (C10H18O) is is the main component in a mixture of terpene chemical compounds that can be derived from citronella oil. ... Intramolecular describes a process or characteristic limited within the structure of a single, or each molecule; a property or phenomenon limited to the extent of a single, or each molecule. ... Niobium pentachloride or Niobium(V) chloride is the chloride of niobium and yellow fine crystalline powder. ... A catalyst (Greek: καταλύτης, catalytēs) is a substance that accelerates the rate (speed) of a chemical reaction without itself being transformed or consumed by the reaction (see also catalysis). ... In chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom. ...

Image File history File links Carbonyl_ene_reaction. ...

References

• Succinic acid, cinnamyl Christian S. Rondestvedt, Jr Organic Syntheses, Coll. Vol. 4, p.766; Vol. 31, p.85 Online Article open access publication
• Intramolecular ene reactions catalyzed by NbCl₅, TaCl₅ and InCl₃ Carlos Kleber Z. Andrade; Otilie E. Vercillo; Juliana P. Rodrigues; Denise P. Silveira J. Braz. Chem. Soc. vol.15 no.6 São Paulo Nov./Dec. 2004 [Online Article] open access publication