STEREOCHEMISTRY, PART 62 - ACETOLYSIS OF TRITERPENOID P-TOLUENESULFONATES, PART 2

Synthesis of p-toluenesulfonates 8b and 9b and of labelled analogs is described and previous assignements of proton NMR signals for quaterna ry methyl groups are confirmed. Acetolysis of these p-toluenesulfonate s in the presence of NaOAc gave both substitution and elimination prod ucts. Substitution could be accounted for by bimolecular processes (SN 2 on carbon, SAN on sulfur). Kinetics confirmed the intervention of bi molecular processes for 8b. Elimination products came for a great pan from intermediates formed by hydride and/or methyl shifts. All rearran ged products could be explained by plain sigmatropic rearrangements or by contact ion pair rearrangements. Attention is drawn to the close r esemblance between sigmatropic rearrangements and contact ion pair rea rrangements. (C) 1998 Elsevier Science Ltd. All rights reserved.