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The fully substituted 12-membered macrocycle of the cubitane-type diterpenoids has been assembled in an enantioselective manner following a novel "bridge-and-cut" strategy. Hydroxyalkylation of (S)-carvone afforded a carvonylgeraniol, which underwent transannular cyclization on treatment with samarium diiodide in THF. Fragmentation of one of the shorter bridges of the resulting [8.2.2]bicycle liberated the 12-membered ring with the desired cis-arrangement of the isopropenyl side chains.

From termite soldier's secretions: The enantioselective total synthesis of the diterpene (+)‐cubitene is described. The route is characterized by the cyclization of a carvone‐derived C20 allylphosphate with SmI2, followed by fragmentation to the twelve‐membered ring. As a result, perfect stereocontrol of the isopropenyl‐substituted positions is achieved.

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Aiming at the assembly of marine-derived diterpenoids, the synthesis and cyclization of a-geranylated carvones was investigated. 3-Hydroxyalkylation of side-chain hydrogenated carvone with geraniol-derived aldehydes gave access to diterpenoid allyl phosphates. It was shown that retro-aldol fragmentation of ring-hydrogenated 3-hydroxyalkylcarvones is surprisingly facile, because the preferred conformation resembles a Zimmerman-Traxler type transition-state. The hitherto unknown rearranged eunicellane skeleton can be obtained in one step by treatment of an a,b-unsaturated diterpenoid with samarium diiodide generated in situ in THF. NOESY-based structure analysis revealed the presence of an ansa bridge across a twist-boat six-membered ring.