Formal homoiodo allylsilane annulations: dual total syntheses of (±)-hirsutene and (±)-capnellene.

Dual total syntheses of (±)-hirsutene and (±)-capnellene, two typical linear triquinane sesquiterpenes, were achieved via a formal [3 + 2] annulation strategy, as illustrated schematically. Cyclic homoiodo allylsilanes were employed as key bifunctional synthons in the synthesis, which were readily prepared from the corresponding cyclopropanated cyclopentenones. A formal [3 + 3] annulation approach for the elaboration of the bicyclic framework of the Eudesmane sesquiterpenoids based on this type of synthon was also developed.