Shionone (I) is a tetracyclic triterpene ketone, C_<30>H_<50>O, isolated from the roots of Aster tataricus L. The partial structure (III) has been deduced for shionone on the basis of chemical degradations. The structure (III) has been extended to (I) by means of biogenetic considerations. In the present report, the nature of rings C and D is clarified and the conversion of friedelin into methyl tetranorshionanoate is described. These evidences lead without the help of biogenetic considerations to the structure (I) for shionone. Shionone (I) was transformed into heptanorshionanone (IV). The IR and ORD data of (IV) indicate that the ring D of (IV) must be a six membered ring with a ring fusion (C/D) of 5 α-cholestan-3-one or -2-one type. The mass spectrum of ethylene ketal of (IV) shows a peak at m/e 99 (fragment ion "a") (base peak) together with a strong peak at m/e 139 ("b"). This means that (IV) must be 20-oxoheptanorshionane (XXII). The NMR studies on the shionone derivatives show that the side-chain bears a 1,3-diaxial relationship to an α-(axial) methyl group at C_<13>. The configuration of the side-chain, therefore, must be α(axial). Structure (I) follows for shionone. The structure (I) was fully demonstrated for shionone by the following transformations: Friedelin (II)→(XXVIII)→(XXIX)→(XXX)→(XXXI)→(XXXII)→norshionene (XXVI)→methyl tetranorshionanoate (XXVII).
