Recent Advances in the Reactions of Halopolicyclic Alkanes by the SRN1 Mechanism

ANA N. SANTIAGO; SANDRA E. MARTÍN; ROBERTO A. ROSSI

TRENDS IN ORGANIC CHEMISTRY

Research Trends

Año: 2001 vol. 9 p. 1 - 16

It is well known that alkyl halides react with nucleophiles by the polar mechanisms SN1 or SN2. When polar mechanisms are not operative due to steric, electronic or strain factors, the most important mechanism is the SRN1. Nucleophilic substitution reactions of cycloalkyl halides strongly depend on the reaction conditions. The ring size is of primary importance in determining the reactivity of the substrate towards nucleophiles. Another contributing factor in determining reactivity is the strain energy. Bridgehead halides react slowly by polar nucleophilic substitution reactions. However, they do react by the SRN1 mechanism with moderate to high yields. The reactivity is remarkably dependent on the strain energy, the nature of the leaving groups, the nucleophiles and/or the solvent. When the bridgehead compound bears a π acceptor, i.e. carbonyl group, the reaction with nucleophiles is much faster (intramolecular redox catalysis). When the substrate has two leaving groups, the monosubstitution and/or disubstitution products can be formed, depending on the nature of the leaving group, the nucleophiles and the reaction conditions. In some cases when the structure of the bridgehead moiety is appropriate, propellanes are rendered the most important products.