The Cope reaction or Cope elimination, developed by Arthur C. Cope, is an

elimination reaction An elimination reaction is a type of organic reaction in which two substituents are removed from a molecule in either a one- or two-step mechanism. The one-step mechanism is known as the E2 reaction, and the two-step mechanism is known as the E1 r ...

of the N-oxide to form an

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, a ...

and a hydroxylamine.

Mechanism and applications

The reaction mechanism involves an intramolecular 5-membered cyclic transition state, leading to a ''syn'' elimination product, an E_i pathway. This organic reaction is closely related to the

Hofmann elimination Hofmann elimination is an elimination reaction of an amine to form alkenes. The least stable alkene (the one with the least number of substituents on the carbons of the double bond), called the Hofmann product, is formed. This tendency, known as ...

, but the base is a part of the leaving group. The amine oxide is prepared by oxidation of the corresponding

amine In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent suc ...

with an oxidant such as

meta-chloroperoxybenzoic acid ''meta''-Chloroperoxybenzoic acid (mCPBA or ''m''CPBA) is a peroxycarboxylic acid. A white solid, it is used widely as an oxidant in organic synthesis. mCPBA is often preferred to other peroxy acids because of its relative ease of handling. mC ...

(''m''CPBA). The actual elimination just requires heat. : Illustrative of the Cope reaction is a synthesis of methylenecyclohexane: : MethyleneCyclohexaneByCopeReaction

Piperidines are resistant to an intramolecular Cope reaction but with

pyrrolidine Pyrrolidine, also known as tetrahydropyrrole, is an organic compound with the molecular formula (CH2)4NH. It is a cyclic secondary amine, also classified as a saturated heterocycle. It is a colourless liquid that is miscible with water and most ...

and with rings of size 7 and larger, the reaction product is an unsaturated hydroxyl amine. This result is consistent with the 5-membered cyclic transition state. : CopeReactionJACS82-4656

Reverse reaction

The reverse or retro-Cope elimination has been reported, in which an N,N-disubstituted hydroxylamine reacts with an alkene to form a tertiary N-oxide. The reaction is a form of hydroamination and can be extended to the use of unsubstituted hydroxylamine, in which case oximes are produced.

Related processes

Sulfoxides can undergo an essentially identical reaction to produce sulfenic acids which is important in the antioxidant chemistry of garlic and other plants of the genus

Allium ''Allium'' is a genus of monocotyledonous flowering plants that includes hundreds of species, including the cultivated onion, garlic, scallion, shallot, leek, and chives. The generic name ''Allium'' is the Latin word for garlic,Gledhill, David ...

. Selenoxides likewise undergo selenoxide eliminations. Other E_i reactions proceed similarly.

References

{{DEFAULTSORT:Cope Reaction Elimination reactions Olefination reactions Name reactions