Partialsynthesen und Reaktionen von Abietanderivaten (Lanugonen) aus Plectranthus lanuginosus und verwandten Verbindungen

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Abstract
Partial Syntheses and Reactions of Abietanoid Derivatives (Lanugones) from Plectranthus lanuginosus and of Related CompoundsInterconversions by partial syntheses of several lanugones establish their absolute configuration at C(15). Unexpected reactions exemplify the unique reactivity of these abietanoic diterpenes, ‐ Lanugone O (4) was prepared in several steps from (15S)‐coleon C (8a; Scheme 2) thus establishing its (15S)‐configuration. One of the intermediates, the 12‐O‐acetyl‐6‐oxoroyleanone 12, through acetyl‐migration sets up an equilibrium with the vinylogous quinone 13 (Scheme 3). ‐ The chirality at C(15) in the dihydrofuran moiety of lanugone Q (16) was proven by acid‐catalyzed conversion of lanugone O (4) to 16. ‐ Instead of the usual nucleophilic attack shown by quinomethanes, lanugone L (1) is electrophilically substituted at C(7) by acetic anhydride/pyridine (Scheme 1). ‐ In a homosigmatropic [1,5]‐H‐shift, lanugone G (17) in solution is converted to the corresponding allyl substituted royleanone 18 (Scheme 4). ‐ Methanolysis of lanugone J (19) leads to the expected royleanone 20 having the 2‐methoxypropyl side chain (Scheme 5). Similar reactions were found in acetolytic reactions. However, treatment‐of spirocoleons with SOCl2/DMF produces mainly 12‐deoxyroyleanones with allyl‐ and 2‐chloropropyl groups, i. e. 19→26 and 27; 28 → 29. The possible natural occurrence of these compounds is emphasized.

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