Stereochemistry of base promoted β-elimination from dihalocycloalkanes and 2-monosubstituted norbornanes

Elimination reactions are one of the four fundamental classes of reactions of organic compounds. The most frequently encountered type of elimination is β-elimination which involves the heterolytic cleavage of two bonds and the formation of a new multiple bond linkage. This process can be accomplished by a variety of mechanistic possibilities ranging from multistep reactions to concerted processes with different electron distributions and geometries. Three basic mechanisms of 3-elimination reactions have been recognized. These mechanisms differ chiefly in the timing of the carbonhydrogen and carbon-leaving group cleavage and are termed El, ElcB, and E2 mechanism.