19.22 : Amines to Alkenes: Cope Elimination

Cope elimination, much like Hofmann elimination, produces the less-substituted alkene as the major product through eliminating N,N–dimethyl hydroxylamine from an amine oxide instead of a tertiary amine from a quaternary ammonium salt.

The amine oxide is formed from the oxidation of a tertiary amine by hydrogen peroxide.

The full positive charge on the nitrogen atom promotes Cope elimination, which is a concerted elimination process that follows syn stereochemistry under thermal conditions.

The amine oxide intramolecularly abstracts the less hindered β proton, followed by a cyclic flow of electrons that ultimately leads to the loss of the leaving group and the formation of the less-substituted alkene.

The participating atoms involved in the transition state have a nearly planar arrangement, with the β hydrogen and the leaving group oriented in a syn manner.

Cope elimination, unlike Hofmann elimination, does not require an external base as the amine oxide functions as the base in the reaction.