Cope Elimination reaction

Theory and Defination :

This reaction is developed by Arthur C. Cope.
The cope elimination is a one-step process of oxidation of tertiary amine with a peroxide forms an N-oxide that undergoes an intramolecular deprotonation with syn stereoselectivity upon heating. This reaction is known as cope elimination. Because the cope elimination involves a cyclic transition state, it occurs with stereo chemistry.
Cope elimination generally gives the same orientation as Hoffman elimination resulting in less substituted alkene. This elimination reaction is also called cope reaction.

General Reaction :

Mechanism :

Cope reaction is believed to take place through a cyclic transition state as depicted below.

The formed transition state behaves as :

The direction of the cope elimination is governed almost entirely by the number of hydrogen atoms at the various beta position. Therefore, there is no preference for the formation of the least substituted alkenes unlike in the Hoffman elimination reaction.It is to be noted that cope elimination is cis and needs lower temperatures than the pyrolysis of quatenary ammonium hydroxides.

Examples and Application :

The synthetic utility of the cope elimination is comparable to the Hofmann elimination of quatenary ammonium hydroxides, but takes place at lower temperatures.
The Cope elimination is almost free of side reactions due to the intramolecular nature of the elimination. However, in certain cases, the product alkene may isomerize to the more stable conjugated system, and allyl-or benzyl migration is sometimes observed to give O-allyl or benzyl substituted hydroxyamines. Cyclic amine oxides can also be pyrolysed but with 6-membered rings the reaction is usually low-yielding or does not occur.

1) The amine is oxidized with hydrogen peroxide to give oxide which on Heating gives methylenecyclohexane and N,N-dimethylhydroxylamine through an intramolecular elimination reaction.