Abstract The synthesis of the (±)-form of the marine sesquiterpene (–)-Δ 9 (12)-capnellene (1) by double application of the a-alkynone cyclization is described. Starting with 2, 2, 5-trim ethylcyclopentanone (2), the elaboration of the tricyclo [6.3. 0.0 2, 6] undecane C-skeleton of 1 proceeded through the a-alkynone 3, which was cyclized thermally to the bicyclo [3.3. 0] octenone 4. For the anellation of the third five-membered ring, 4 was transformed into the ...
