Kuczynska K, Jaźwiński J, Pakulski Z, Cmoch P, Luboradzki R. Oxidative Functionalization of Trinor-18α-olean-17(22)-ene Derivatives. Annulation of the E-Ring by an Intramolecular Aldol Reaction.
J Org Chem 2021;
86:7636-7647. [PMID:
34033473 DOI:
10.1021/acs.joc.1c00697]
[Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
cis-Dihydroxylation of trinor-18α-olean-17(22)-ene 2 with osmium tetroxide led to diol 9. Its cleavage with lead tetraacetate gave tetracyclic ketoaldehyde 10. By comparison, the ozonation of trinor-18α-olean-17(22)-ene 2 in the presence of p-toluenesulfonic acid gave the corresponding ketoacetal 12. Both products were subjected to an intramolecular aldol reaction under the acidic conditions and yielded unusual triterpenes bearing a bicyclo[4.3.1]decane fragment (22). Further manipulation of the protective groups afforded compounds useful in triterpene synthesis, especially in the preparation of potentially biologically active saponins based on a tetracyclic terpene core.
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