The paper reviews the known examples of cyclic terpenoids produced from open chain polyenic precursors by an "unusual" biosynthetic pathway, involving selective electrophilic attack on an internal double bond followed by cyclization. The resulting compounds possess cyclic backbones with pendant terminal prenyl groups. Synthetic approaches applied for the synthesis of such specifically functionalized compounds are also discussed, as well as biological activity of reported representatives.

The bicyclic core of the halimanic framework is synthesized in optically active form by an acid-induced rearrangement of a homo­drimanic epoxide. The substrate can follow two different pathways under acidic treatment. Using fluorosulfonic acid as a promoter at low temperature favors ring contraction to a perhydrindanic structure. In contrast, milder acids at higher temperatures bring about predominantly an angular methyl migration and formation of the halimanic bicyclic system. In particular, an acidic pillared clay selectively promoted this transformation.

Review: 182 refs.