Investigations Directed Toward the Total Synthesis of Shionone

An approach to the total synthesis of the tetracyclic triterpene shionone i is described. The key intermediate ii was prepared in 17 steps (3.0% overall yield) from 2-methyl- 1,3-cyclohexanedione. Generation of the essential trans, disubstituted C/D ring fusion of ii was accomplished via the stereospecific formation and cleavage of a fused methoxy- cyclopropane system. An additional 12 steps served to convert the ketone ii into the ketal-ketone iii (12.5%) which requires only addition of the side chain to complete the total synthesis. See abstract in PDF for figures i,ii and iii