Stereochemistry. Part 62: Acetolysis of Triterpenoid p-Toluenesulfonates. Part 2

Article abstract of DOI:10.1016/S0040-4020(98)00196-3

Synthesis of p-toluenesulfonates 8b and 9b and of labelled analogs is described and previous assignements of proton NMR signals for quaternary methyl groups are confirmed. Acetolysis of these p-toluenesulfonates in the presence of NaOAc gave both substitution and elimination products. Substitution could be accounted for by bimolecular processes (SN2 on carbon, S_AN on sulfur). Kinetics confirmed the intervention of bimolecular processes for 8b. Elimination products came for a great part from intermediates formed by hydride and/or methyl shifts. All rearranged products could be explained by plain sigmatropic rearrangements or by contact ion pair rearrangements. Attention is drawn to the close resemblance between sigmatropic rearrangements and contact ion pair rearrangements.