The dehydrochlorination of 3β-chloro-5β-cholestane. New syntheses of 5β-cholest-2-ene and 5β-cholest-3-ene

✍ Scribed by G. Bellucci; F. Macchia; V. Malaguzzi

• Publisher: Elsevier Science
• Year: 1966
• Tongue: French
• Weight: 238 KB
• Volume: 7
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(00)90311-3

✦ Synopsis

Although most cholestenes of the 56 series have been throughly investigatea' only few informations can be found in the literature about the analogous 5P-derivatives. It has been reported, for instance, that 5)3-cholestan-3/j-01 tosylate is transformed by alumina into 5P-cholest-2-ene,' and that the dehydrochlorination of 3+ and 3p-chloro-5+cholestane, as well 'l'he brominstion of pure 11,under the conditions specified e.;~ove, :F:ve a tiibrornide, m.p. 74-76' (from acetone), which ~18s isomerized to the dibromide, m.p. 165-167', referred to above. Although a more throu,;h study of these reactions remains to be done, it is most likely, in consideration of the similar reactions in the 5a-series," that the lower-melting dibromide is the diaxial 2u,3p-dibromo-5j3-cholestane (XI), which isomerizes to the diequatorial 2P,3a-dibromo derivative (XII).

The incorrect report on the exclusive formation of 5p-cholest-2-ene (II) from 3p-chloro-5fi-cholestane was probably due to the fact that II and III have very similar physical properties, that their mixtures have rather sharp melting points, with very little depression, and that -they are difficult to sepsrate by conventional techniques, such as fractional crystallization.

It would therefore be advisable and interesting to study again all those elimination reactions which can lead to II or III, a task which is now easy with the aid of GLC analysis.