Bismuth triflate-catalyzed Wagner-Meerwein rearrangement in terpenes. Application to the synthesis of the 18α-oleanane core and A-neo-18α-oleanene compounds from lupanes?

Organic & Biomolecular Chemistry Pub Date: 2008-12-09 DOI: 10.1039/B814448F

Abstract

The use of bismuth(III) salts as catalysts for the Wagner-Meerwein rearrangement of lupane derivatives with expansion of ring E and formation of an additional O-containing ring is reported. This process has also been extended to other terpenes, such as the sesquiterpene (?)-caryophyllene oxide. When the reaction was performed with oleanonic acid, 28,13β-lactonization occurred, without Wagner-Meerwein rearrangement. Under more vigorous reaction conditions, dehydration of the 3β-hydroxyl group and subsequent additional Wagner-Meerwein rearrangement led to the selective synthesis of A-neo-18α-oleanene compounds, in very high yields.

Graphical abstract: Bismuth triflate-catalyzed Wagner-Meerwein rearrangement in terpenes. Application to the synthesis of the 18α-oleanane core and A-neo-18α-oleanene compounds from lupanes
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