Ophiobolin ring system

The [4+ 4]-cycloaddition reaction of tethered bis-dienes has been used by Wender and co-workers in total synthesis as exemplified in syntheses of ( )-salsolene oxide and (-l-)-asteriscanolide (Scheme 28). In the synthesis of ( )-salsolene oxide, a nickel(0)-catalyst cleanly effects the cycloaddition of the two conjugated dienes in compound 93 to afford the bicyclo[5.3.1]undecadiene in a good yield and with moderate selectivity.99 The first synthesis of (-l-)-asteriscanolide was accomplished in only 13 steps. The key [4+ 4]-cycloaddition reaction efficiently set the requisite eight-membered ring of (-l-)-asteriscanolide in good yield and with excellent diastereoselectivity.100 The diastereoselective [4 + 4]-cycloaddition has also been applied to the synthesis of the core ring system found in several sesterterpenes such as the ophiobolins (Scheme 28).101... 

Dauben and Hart have employed the ring contraction-ring expansion annelation sequence depicted in Scheme 34 to effect the first synthesis of the tri-cyclo[9,3,0,0 ]tetradecane ring system characteristic of the ophiobolin sester-terpenes. ... 

Members of the ophiobolin and fussicoccin families of terpenes are fungal metabolites that contain a [5-8-5] ring system as exemplified by ophiobolin F 73 (Figure 19.6). Simpkins and coworkers decided to develop a general strategy to this class of compounds due in part to the biological activity of this compound class [46]. Treatment of... 

---