Frichert Alex, Jones Peter G, Lindel Thomas
Institute of Organic Chemistry, TU Braunschweig, Hagenring 30, 38106 Braunschweig, Germany.
Institute of Inorganic and Analytical Chemistry, TU Braunschweig, Hagenring 30, 38106 Braunschweig, Germany.
Beilstein J Org Chem. 2018 Sep 20;14:2461-2467. doi: 10.3762/bjoc.14.222. eCollection 2018.
The first synthesis of diterpenoid eunicellane skeletons incorporating a 1,3-cyclohexadiene moiety is presented. Key step is a low-valent titanium-induced pinacol cyclization that proved to be perfectly diastereoselective. Determination of the relative configuration of the diol was aided by the conversion to the diastereomer by oxidation and reduction. Conformational analysis of some of the resulting diols obtained under McMurry conditions was complicated by the presence of several conformers of similar energy. The pinacol coupling appears to start at the ketone, as indicated by the selective reduction of non-cyclizing cyclohexane systems that were synthesized from limonene oxide. The title compounds and their synthetic precursors are prone to aromatization on contact with air oxygen. Attempted synthesis of cyclohexene-containing eunicellane bicycles by elimination of water from tertiary alkynyl carbinols afforded novel allene systems. Our study may be of help towards the total synthesis of solenopodin or klysimplexin derivatives.
首次报道了含有1,3 - 环己二烯部分的二萜类柳珊瑚烷骨架的合成。关键步骤是低价钛诱导的频哪醇环化反应，该反应被证明具有完美的非对映选择性。通过氧化和还原转化为非对映异构体有助于二醇相对构型的确定。在麦克默里条件下得到的一些二醇的构象分析因存在几个能量相似的构象体而变得复杂。频哪醇偶联反应似乎从酮开始，这由从氧化柠檬烯合成的非环化环己烷体系的选择性还原所表明。标题化合物及其合成前体在与空气中的氧气接触时容易发生芳构化。尝试通过从叔炔基甲醇中消除水来合成含环己烯的柳珊瑚烷双环化合物，得到了新型丙二烯体系。我们的研究可能有助于海葵毒素或克利斯辛衍生物的全合成。
