Neighboring Carbon and Hydrogen. XXII. Homoallylic Systems. The Preparation and Behavior of Certain 3,5-Cyclosteroids

Homoallylic systems offer an interesting departure from the more familiar allylic ones. In this connection, 5-cholesten- 3β-yl and the related 3,5-cyclocholestan-6β- and 6α-yl derivatives are interesting. In the present work, the preparation of “i-cholesterol” has been improved, and the configurations of the 3,5-cyclocholestan-6-ols have been discussed. Both 3,5- eyclocholestan-6-yl trichloroacetates have been prepared, and their rearrangement and solvolysis have been studied. While cholesteryl trichloroacetate methanolyzes with acyl-oxygen cleavage, both 3,5-cyclocholestan-6-yl trichloroacetates do so with alkyl-oxygen cleavage. In methanol-chloroform, cholesteryl toluenesulfonate and the 3,5-cyclocholestan-6-yl trichloroacetates yield a mixture of methyl ethers, 90 ± 2% 3,5-cy[clocholestan-6β-yl and 10 ± 2% cholesteryl. These results are ascribed to the occurrence of a common homoallylic hybrid carbonium ion intermediate in the solvolysis of all three compounds. The results cannot be discussed on the basis of only dissociated forms of the carbonium ions. In 90% dioxane, substantial ion pair return accompanies hydrolysis of both 3,5-cyclocholestan-6-yl trichloroacetates. Thus, cholesteryl trichloroacetate is produced during hydrolysis. Even in methanol-chloroform, a few per cent, of cholesterol, by way of cholesteryl trichloroacetate, is obtained from either 3,5-cyclocholestan-6-yl ester.