Common synthetic strategy for optically active cyclic terpenoids having a 1,1,5-trimethyl-trans-decalin nucleus: syntheses of (+)-acuminolide, (−)-spongianolide A, and (+)-scalarenedial

We have developed a simple and practical method for providing enantiomerically pure bi-, tri-, and tetracyclic frameworks having a 1,1,5-trimethyl-trans-decalin nucleus, and demonstrated their utility for terpenoid synthesis. Thus, we achieved the stereocontrolled total syntheses of (+)-acuminolide as a bicyclic, (−)-spongianolide A as a tricyclic, and (+)-scalarenedial as a tetracyclic terpenoid from the corresponding optically pure cyclic β-ketoesters, which were obtained by repeating the same method of the ring construction, including the olefin cyclization with Lewis acid, followed by simple optical resolution using chiral auxiliaries for acetal formation, respectively. This is a general and valuable strategy for the synthesis of enantiomerically pure cyclic terpenoids having the 1,1,5-trimethyl-trans-decalin nucleus.