Chapter 3 Elimination Reactions

Abstract

This chapter discusses elimination reactions. An organic molecule undergoes an elimination reaction when it loses two atoms or groups of atoms that are subsequently not replaced. Most frequently, the fragments are removed from the adjacent atoms and the processes are called beta-eliminations or 1,2-eliminations. Many well-known synthetic organic reactions fall into this category: (1) Hofmann elimination, (2) Cope elimination, and (3) Chugaev reaction. The mechanisms of reactions, leading to olefinic products, which occur by beta-elimination processes, are discussed in this chapter. The majority of olefin-forming reactions of synthetic importance are beta eliminations, which usually involve the removal of the elements HX, from the adjacent carbon atoms. The processes are often base-catalyzed but will also occur in the absence of bases under solvolytic conditions. The orientation of elimination is greatly influenced by the choice of the leaving group, the substituents at the alpha and beta carbons and the base and solvent. In many cases, the direct products of elimination are unstable under the reaction conditions and the intermediacy of a three membered ring is established by carefully combining the kinetic studies and subsequent product analysis. This approach is adequately illustrated by the well-known Neber, Ramberg-Backlund, and Favorskii rearrangements.