TY - JOUR A1 - Frichert, Alex A1 - Jones, Peter G. A1 - Lindel, Thomas T1 - Synthesis of eunicellane-type bicycles embedding a 1,3-cyclohexadiene moiety JF - Beilstein Journal of Organic Chemistry PY - 2018/// VL - 14 SP - 2461 EP - 2467 SN - 1860-5397 DO - 10.3762/bjoc.14.222 PB - Beilstein-Institut JA - Beilstein J. Org. Chem. UR - https://doi.org/10.3762/bjoc.14.222 KW - conformational analysis KW - low valent titanium KW - marine natural products KW - pinacol coupling KW - ten-membered rings N2 - 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. ER -