Theory and Defination :
The cope elimination is a process of oxidation of tertiary amine using peroxide to forms an N-oxide which on heating undergoes an intramolecular deprotonation with syn stereoselectivity . This reaction is known as cope elimination. This reaction is developed by Arthur C. Cope. 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 :
Examples and Application :
The synthetic utility of the cope elimination is comparable to the Hoffman elimination of quaternary ammonium hydroxides, but takes place at lower temperatures.The Cope elimination is almost free of side reactions due to the intra molecular 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 pyrolyse but with 6-membered rings the reaction is usually low-yielding or does not occur. The direction of the cope elimination is governed almost entirely by the number of hydrogen atoms at the various ββ-positions, and therefore there is no preference for the formation of the least substituted alkene unlike in the Hoffman elimination reaction. Upon pyrolysis N-cyclohexyl derivatives however form predominantly exocyclic olefin's, since the formation of the endocyclic double bond would require the cyclohexane ring to be almost planar in the transition state.
1) The amine is oxidized with hydrogen peroxide to give oxide which on Heating gives methylene cyclohexane and N,N-dimethyl hydroxyl amine through an intramolecular elimination reaction.
