Triterpenoids with a β-ketonitrile group in five-membered ring A were synthesized via intramolecular oxonitrile cyclization of C-3 methyl esters of 1-cyano-substituted 2,3-seco-triterpene acids. The intramolecular cyclization to form the triterpene ketonitriles and subsequent reduction of the oxo groups to give C-1 and C-3 substituents in the β-orientation were confirmed to be stereoselective. Alkaline hydrolysis of the ketonitriles reduced the cyano groups to form the corresponding 3-oxo-2-nor-derivative while reduction and acylation of the β-hydroxynitrile formed an α,β-alkenenitrile fragment in the triterpenoid five-membered ring A.

中文翻译：

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五元环A中含β-酮腈片段的三萜类化合物的合成与转化

在五元环 A 中具有 β-酮腈基团的三萜类化合物是通过 1-氰基取代的 2,3-seco-三萜酸的 C-3 甲酯的分子内氧腈环化合成的。分子内环化形成三萜酮腈和随后的氧代基团还原以在 β 取向中产生 C-1 和 C-3 取代基被证实是立体选择性的。酮腈的碱水解还原氰基以形成相应的 3-oxo-2-nor-derivative，而 β-羟基腈的还原和酰化在三萜类五元环 A 中形成α,β-烯腈片段。