Intramolecular Cyclization of 2‐Alkynylphenylcarbonyls With a Pendant Double Bond under Copper Catalysis: A General Approach to Norabietane Core Structure

Abstract Synthetic routes leading to [6,6,6]‐tricyclic compounds were reported using metal catalysts from ene‐yne‐aldehydes in our group. Based on this result, the synthesis of various [6,6,6]‐tricyclic compounds is reported using transition metal‐catalyzed cyclization from enyne‐carbonyl substrates containing H, Me, Ph, OMe, CO 2 Me, and CO 2 i ‐Pr groups. Tricyclic compounds containing the CO 2 Me group would be the prospective precursors of the natural product Lepenine.