Chirale Bausteine zur Synthese von Triquinan‐Sesquiterpenen: Derivate des 2‐Methylbicyclo[3.3.0]octan‐3‐ols aus Catalpol

Scutellaria subvelutina was found to be an excellent source of the catalpol ester scutellarioside I (3) and this was chemically converted into 5,7‐dideoxycynanchoside. The partially protected iridoid glucosides, 8,10:4′,6′‐di‐O‐isopropylidene‐5,7‐dideoxycynanchoside (6) and 6,2′,3′,6′‐tetra‐O‐benzoylantirrhinoside (10), as well as the fully protected 5,6‐O‐ isopropylidene‐2′,3′,4′,6′‐tetra‐O‐acetylantirrhinoside (8a) were subjected to ozonolysis with reductive work‐up using sodium tetrahydridoborate. Using a large excess of reductant, the reaction mixtures from 6 and 8a were reduced completely to give the respective polysubstituted cyclopentanols, while reduction of the ozonolysis product from 10 could be stopped at the hemiacetal 11 by employing a smaller amount of reductant.

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Ozonolysis of Protected Iridoid Glucosides

Franzyk¹,

Rasmussen

Jensen

1998

Eur. J. Org. Chem.

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Synthese von enantiomerenreinem (−)‐Hypnophilin

et al. 1990

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diese Reaktionen[I6I IaBt darauf schliekn, dal3 EM-Werte fur Hexenylumlagerungen bis zu lo5 M betragen konnen. u Diese Daten sprechen zusammen mit den von uns direkt aus Nitroxidreaktionen erhaltenen Werten dafiir, daB intramolekulare H-Atom-Transferreaktionen wie H-Ionen-Transferreaktionen generell niedrige EM-Werte haben, wahrend intramolekulare Radikaladditionen wie Ionenadditionen wohl generell vie1 hohere haben. Fur Ionenreaktionen gibt es mehrere Interpretationen dieses divergenten Verhaltens['* "* "]; wahrscheinlich tragen einige Faktoren dazu bei. Der Vorschlag, daB der intramolekulare Protonentransfer enthalpisch wegen der Unerreichbarkeit eines colinearen (X . . . H . . . Y)-Ubergangszustands signifikant ungiinster ist *-'01, scheint, obwohl attraktiv, durch neue Berechnungen von Dorigo und Houk['" widerlegt zu sein. Vom Standpunkt der Synthese ist klar, daB der intramolekulare Atomtransfer ebenso wie die intramolekulare Addition oft hinreichend schnell fur praparativ niitzliche Umwandlungen ist. Unsere Bemiihungen, das 3a-Cholestanolderivat 8 (Fp = 159-160"C)[81 ferngesteuert zu oxidieren, fiihrten jedoch zu einem sehr bestandigen Nitroxid, das keine Anzeichen einer intramolekularen Reaktion zeigte. ; (€)-(PhCH $ 2 . 103-30-0; PhCON(O)fBu, 35822-90-3. [l] Wassersfoffatomtransfers schliekn die wohlbekannten Hoffmann-Loffler-Freytag-[M. E. Wolff, Chem. Rev. 63 (1963) 551 und Barton-Reaktionen [R. H. H e w , Adv. Free Radical Chem. 3 (1969) 831 ein; neuerdings werden versfarkf intramolekulare Additionen genufzt ; siehe beispielsweise D.

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Synthesis of Enantiomerically Pure (−)‐Hypnophilin

Weinges

Dietz

Oeser

et al. 1990

Angew. Chem. Int. Ed. Engl.

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Chirale Bausteine zur Synthese von Triquinan‐Sesquiterpenen: Derivate des 2‐Methylbicyclo[3.3.0]octan‐3‐ols aus Catalpol

Cited by 6 publications

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Ozonolysis of Protected Iridoid Glucosides

Ozonolysis of Protected Iridoid Glucosides

Synthese von enantiomerenreinem (−)‐Hypnophilin

Synthesis of Enantiomerically Pure (−)‐Hypnophilin

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