Construction of the basic skeleton of ophiobolin A and variecolin.

Ophiobolin and variecolin type sesterterpenoids belong to cyclooctane-containing natural products. Both sesterterpenoids have challenging structures and appealing biological activities. We envisioned that a key tandem ring closing metathesis of dienynes could provide the basic skeleton of ophiobolin A and variecolin. We report herein the detailed reactivities of the dienynes which furnished the 5-8-5 and 5-8-6-5 rings efficiently.