Synthesis of (±)-Pentalenene

✍ Scribed by Shikai Zhao; Goverdan Mehta; Paul Helquist

• Book ID: 104225900
• Publisher: Elsevier Science
• Year: 1991
• Tongue: French
• Weight: 233 KB
• Volume: 32
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(00)93547-0

✦ Synopsis

A short, formal synthesis is reported for pentalenene. The key steps are copper-catalyzed 1,4-addition of isobutylmagnesium bromide to a cyclooctenone derivative, enolate alkylation with the thiocarbene complex [(@-C5H5)(CO)2Fe=CHSPh]+ PFg-, and cyclopentane ring formation by means of intramolecular C-H insertion, leading to a late intermediate in a previously reported synthesis of pentalenene. Pentalenene (1) is the parent hydrocarbon of the pentalenolactone family of antibiotic antifungal metabolites found in Streptomyces species. Although it was not reported as a natural product from S. griseochromogenes until 1980,2 it had been obtained in work published by Ohfune, Shirahama, and Matsumoto in 1976 concerned with biosynthetically related cation cyclization studies. 3 This early work has been followed by several syntheses of pentalenene."

The strategy for our synthesis (Scheme 1) is based upon annulation of a gem-dimethylated cyclopentane ring onto the 5-hydroxy-2-cyclooctenone derivative 3 leading to 2. The bicyclic compound 2 and similar intermediates have previously been reported to undergo a biomimetic transannular cationic cyclization3~4h.e.f to give pentalenene.