Reactions of 5-alpha-hydroxy steroids. VII. The westphalen rearrangement of some 3-beta-substituted-6-beta-acetoxy-5-alpha-hydroxy cholestanes.
Abstract Product analyses and kinetic studies of the reactions of 3β-substituted-6β-acetoxy-5α-hydroxy cholestanes with H 2 SO 4 -Ac 2 O-AcOH reveal a marked dependence of the reactions upon the nature of the 3β-substituent.
Bismuth(III) salt-catalyzed Westphalen and “backbone” rearrangements of 5β,6β-epoxysteroids Synthesis and structural elucidation of new olefinic 19-nor and 18,19-dinorsteroids
A new process using the "ecofriendly" bismuth(III) salts as catalysts for the Westphalen and "backbone" rearrangements of 5 beta,6 beta-epoxysteroids is reported. This method is particularly sensitive to changes on solvent, temperature, stereochemistry of starting epoxysteroid, and its substituent at C17. Depending on the reaction conditions, either Westphalen-type or "backbone" rearranged products were obtained, all being 3 beta-acetoxy-6 beta-hydroxy-substituted. Several new olefinic 19-nor and 18,19-dinorsteroids were obtained and their structural elucidation was fully accomplished using 2D NMR and X-ray crystallography techniques.
Die Isomerisierung von 5‐Methyl‐19‐nor‐koprosten‐Derivaten. I. Teil. Die Irreversibilität der Westphalen‐Lettré‐Umlagerung
Dehydration of 5-hydroxy cholesterol derivatives is attended by C–10 to C–5 methyl migration (Westphalen-Lettre rearrangement) only if a β-substituent is present at C–6. In the absence of such a substituent dehydration and dehydrochlorination of 5-hydroxy and 5-chloro derivatives respectively yield mainly 5-cholestenes in a rate-controlled 1,2-elimination process.