Cope Elimination or Cope Reaction
Cope elimination is also known as Cope reaction in which amines are converted into quaternary ammonium salts and later to alkenes. It involves treatment of a tertiary amine with hydrogen peroxide to obtain amine oxide which on heating gives N,N-diakylhydroxyl amine and an alkene.
Mechanism of Cope Elimination
The elimination proceeds via a five-membered cyclic transition state. This is a concerted internal elimination during which, the amine oxide acts both as a base and a leaving group.
In the Cope elimination, the β hydrogen and the leaving group should be in a syn periplanar orientation for allows the oxygen to attack the proton. For example, the following Cope elimination of a cyclohexyldimethylamine produces one alkene as the major product dictated by the syn stereoselectivity.
Regiochemistry of the Cope elimination does not follow either the Zaitseff or Hofmann path and depends on the presence of hydrogen atoms at the β-positions capable of adopting syn geometry.
Cope elimination occurs under milder conditions than Hofmann elimination. It is particularly useful when a snesitive or reactive alkene must be synthesized by the elimination of an amine.
