Stereochemical Aspects of Acid-Catalyzed Cyclopropane Ring-Opening Reactions. A Stereospecific Pathway to Crinosterol and Brassicasterol

✍ Scribed by Robert W. Lang; Carl Djerassi

• Publisher: John Wiley and Sons
• Year: 1982
• Tongue: German
• Weight: 753 KB
• Volume: 65
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.19820650144

✦ Synopsis

Abstract

It is shown that the acid‐catalyzed ring‐opening of the two diastereoisomeric 23:24‐methylenecholesterols 3 and 5 on treatment with gaseous HCl in acetic acid leads stereospecifically to the naturally occurring crinosterol (4) and brassicasterol (6), respectively (Scheme 1). This isomerization can be viewed as a biomimetic model of an in vivo methylation process of the type already known in plant sterol metabolism (cf. cycloeucalenol → obtusifoliol, 1 → 2). The synthetic application of this method provides a convenient labelling of sterol side chains for tracer experiments. The mechanistic features of the reaction with respect to its particular stereospecificity are discussed.