Olefination

Cope Elimination, also can be termed as cope reaction, represents an elimination reaction of thermal decomposition of amine oxides under a high temperature condition (150-200°C) to produce hydroxylamines and olefins. The underlying mechanism for such elimination reaction mainly involves an intramolecular 5-membered cyclic transition state. Cope reaction is widely applied for olefin synthesis and removal of nitrogen in compounds for its highly efficient and accurate.

Fig 2. Synthesis of Propylene

Wittig reaction, discovered in 1954 by Georg Wittig, is the most widely used for the conversion of carbonyl compounds including aldehydes, ketones, esters, amides and lactams to the corresponding olefin derivatives. It is of great value for the preparation of compounds that interest to the chemical, agrochemical and pharmaceutical industries. However, the sterically hindered ketones in the structure of compounds may lead to a low rate of reaction and a poor yield. In this case, the Horner–Wadsworth–Emmons (HWE) reaction (using phosphonate esters) is recommended as an alternative approach.

Fig 3. Synthesis of Isobutylene

As an improvement of the Wittig reaction, Horner-Wadsworth-Emmons (HWE) reaction is applied in organic chemistry with aldehydes (or ketones) to produce predominantly alkenes. During the process of such reaction, a stable phosphonate carbanion instead of phosphorus ylide is used to react with aldehydes and ketones to produce olefins. An electron-withdrawing group (EWG) is required to be attached to the α-carbon of the phosphonate generally participating in the reaction, so that the four-membered ring intermediate in the reaction is eliminated to generate olefins.

Fig 4. Synthesis of Ethylester