Benzenesulfenyl chloride adds diaxially to 5α-cholest-2-ene (1) yielding 2β-chloro-3α-(phenylthio)-5α-cholestane (3). Assuming that the reaction proceeds via the episulfonium ion (2), this allows the inclusion of these species within the scope of the diaxial opening rule. On heating,3undergoes rearrangement to 3β-chloro-2α-(phenylthio)-5α-cholestane (4). This reaction is the first instance of a diaxial → diequatorial rearrangement of β-halothioethers.Mild oxidation of3gives a mixture of the two sulfoxides epimeric at the sulfur atom (16aand16b). On heating, both sulfoxides suffer pyrolytic elimination, without any sign of diaxial → diequatorial rearrangement. A major product of the elimination, evidently 2-chloro-5α-cholest-2-ene (18), was found to be formed a little more readily from theS-sulfoxide (16b) than from theR-isomer (16a). This observation is in accord with the conclusion of previous investigators that the elimination of the sulfenic acid from an alkyl sulfoxide involves bond formation between the hydrogen and sulfinyl oxygen during the rate determining stage (cf.19).