NATURALLY OCCURRING TERPENE DERIVATIVES .213. HELIFULVANOL ACIDS - NEW DITERPENE WITH HITHERTO UNKNOWN CARBON SKELETON FROM HELICHRYSUM-FULVUM

The aerial parts of H. fulvum afforded, in addition to beyerenic acid and ent-kaurenic acid, 2 new diterpenic acids with the hitherto unknown C skeleton of an isotrachylobane type. The structures of these acids, isolated as their methyl esters, were elucidated by extensive NMR studies, by some chemical transformations and by X-ray structural analysis of the corresponding acetate. The related alcohol on reaction with pyridinochlorochromate afforded a homoconjugated diene probably formed by fragmentation of a cyclopropyl carbinol. The possible biogenesis of the new C skeleton is discussed briefly.