19.22:
Amines to Alkenes: Cope Elimination
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Cope elimination reaction involves the conversion of tertiary amines to alkene using hydrogen peroxide under thermal conditions, as depicted in figure 1.
Figure 1. The Cope elimination reaction
The mechanism of the reaction is illustrated in Figure 2. Here, the oxidation of tertiary amines by hydrogen peroxide yields amine oxide. Subsequently, the thermally induced elimination of the N,N-dimethyl hydroxylamine as leaving group occurs. However, it produces a less substituted alkene as the major product. In this process, amine oxide, in the role of a base, follows the syn stereochemistry and proceeds through a cyclic transition state.
Figure 2. The mechanism of the Cope elimination reaction
Cope elimination is helpful for the synthesis of reactive/sensitive alkenes because the reaction occurs under mild conditions.