Pd‐Catalyzed Cyclotrimerization and Cycloaddition of 5,6‐Didehydrobenzo[8]annulenes (BenzoCOTynes): Formation of Nonplanar Tri[8]annulenes and Diels–Alder Cycloadducts

We investigated the Pd(0)‐catalyzed cyclotrimerization of benzoCOTynes, which afforded a set of regioisomeric tri(benzo[8]annulene) products. Three distinct isomers were isolated and unambiguously characterized by single‐crystal X‐ray diffraction. Ligand modulation proved crucial for enhancing regioselectivity, with P(4‐OMePh) 3 and (S)tBu‐Phox promoting the formation of the symmetric isomers. The resulting polycyclic frameworks exhibited high thermal stability, remaining intact up to 140°C. Furthermore, both benzoCOTyne and benzodiCOTyne readily participated in Diels–Alder cycloadditions, delivering the corresponding adducts in good yields.