Position of the Hydroxyl Group in Lanosterol

Abstract

DEHYDRATION of alcohols of the lanosterol series to the corresponding hydrocarbons has recently been reported by us¹, when the action of both phosphorus pentachloride and phosphorus oxychloride was described. Dihydroagnosterol and dihydrolanosterol, when treated with phosphorus pentachloride, gave iso-agnostadiene (‘iso-γ-lanostatriene'), C₃₀H₄₈, and iso-lanostadiene, C₃₀H₅₀, respectively, and hydrocarbons isomeric with the above dehydration products were obtained with phosphorus oxychloride. We expressed the opinion, based on a consideration of analogous cases in triterpene chemistry, that the phosphorus pentachloride dehydration involved a retropinacoline rearrangement accompanied by a contraction of the terminal ring A of lanosterol, and stated that experiments to confirm this view were in progress. In the meantime, Ruzicka et al.², following pur method of preparation, have reported the results of oxidation experiments on the dehydration product from dihydrolanosterol, and afforded evidence in support of the reaction mechanism suggested above, establishing at the same time the position of the secondary hydroxyl group in lanosterol. The continuation of our work has involved the study of the same series of reactions applied both to iso-agnostadiene and iso-lanostadiene, and in view of Ruzicka‘s publication, we now present a brief summary of our results.