Steroidal sulphur compounds. Part IX. 6α- and 6β-Methylsulphinylcholest-4-ene and related compounds; stereochemical aspects of the allyl sulphoxide–sulphenate rearrangement

Abstract

The rates of several [2,3] sigmatropic allyl sulphoxide–sulphenate rearrangements in the steroidal system have been shown to be influenced by chirality at sulphur. The configuration of the alcohols formed by trapping the sulphenates with piperidine showed that the rearrangements were cleanly suprafaciat with respect to the allyl system. The results of kinetic investigations and equilibration studies suggested that the rate differences were attributable mainly to differences in free energy of the transition states, and consideration of the relative steric compressions in model transition states led to allocations of configuration at sulphur in the sulphoxides. N.m.r. data were in accord with the configurational assignments, and enabled tentative conformational assignments to four of the sulphoxides to be made.