Elimination Reactions

This chapter contains sections titled: E1cB and E2 Mechanisms Pyrolytic Reactions Acid Derivatives Halogen Derivatives Oxygen Derivatives Other Pyrolytic Reactions Elimination Reactions in Synthesis Other Reactions References A theoretical study of the elimination mechanisms involved in the thermal decomposition of 2–thiomethyl–1–chloroethane and 4–thiomethyl–1–chlorobutane was carried out to explore the possible anchimeric assistance of the thiomethyl group in these compounds. The selectivity of hydrobromic elimination appears to be an effect of the electronegativity of the neighbouring heteroatoms themselves rather than the electron-withdrawing effects of the entire heterofunctional group. Mechanistic studies suggest that silver-assisted decarboxylation occurs in an anionic pathway, which leads to an allylation product via transmetalation and reductive elimination. A tentative reaction mechanism involving intermediate elimination of cyanide ion has been proposed. In particular, the elimination pathway in model systems shifts from an E1–like E2 mechanism that is dominated by SN2 substitution to an E1cB mechanism that prevails over SN2 substitution. Density functional theory (DFT) calculations reveal that an acid-base acetolysis mechanism favoured over an oxidative addition/reduction elimination mechanism proceeding via the formation of M(IV) intermediate.