Five coriolin

For his synthesis of the anti-tumour compound diketo-coriolin, Danishefsky needed (9) with its two fused five-membered rings, Enone disconnection suggests two possible precursors. 

The anti-cancer compound coriolin 23 has three fused five-membered rings and two epoxides. Notice that the 3/5 and both 5/5 ring fusions are cis. There have been many syntheses of coriolin, most using stereochemistry from folded precursors.7 We shall feature a couple of examples. Matsomoto s synthesis involves the hydroboration of alkene 24. The addition of borane is cis 25 and the boron is replaced by OH with retention of configuration to give 26. The hydroboration occurred on the outside of the molecule, on the same face as the ring junction hydrogens.8... 

This concept has been applied for the synthesis of the structurally complex and highly oxyfunctionalized triquinane (—)-coriolin (Sch. 31) [61]. Two carbonyl groups, both in the right position for 1,2-acyl shift were present in the trimethyl-functionalized bicyclo[2.2.2]octenone 58. With a site-selectivity of 85% the expected regioisomeric tricyclic dione 59 was formed as a mixture of epimers (Sch. 31). Subsequent transformations involving the annulations of the third five-membered ring as well as epoxidation and hydroxylation steps led to the desired natural product... 

A number of natural sesquiterpenes like hirsutene 90 or corioline 91 have as their common structural unit a system of linearly fused five-membered rings (Scheme 3.21). The standard pathway of the retrosynthetic analysis of this system involves the search for strategic bonds in one of the rings. A, B, or C, disconnection of which would lead to the simplification of the target molecule and eventually to simple cyclopentane derivatives as available starting materials. As a result, diverse synthetic plans were devised and successfully employed in numerous synthetic studies in this field(see also the set of syntheses described in Section 2.23.2). 

Extensive spectroscopic data coriolin has an empirical formula 15 20 5 composed of five structural fragments, - 5 o These... 

Fused Five-membered Rings.—A number of biologically important terpenoids show structures based on the fusion of two or three five-membered rings, e.g. hirsutic acid, pentenolactone, coriolin, capnellane, and retigeranic acid, and efforts directed towards total synthesis of these structural types have burgeoned in the past few years. 

---