Selective Palladium-Catalyzed Cocyclotrimerization of Arynes with Dimethyl Acetylenedicarboxylate: A Versatile Method for the Synthesis of Polycyclic Aromatic Hydrocarbons
derivatives 4,5-difluorobenzyne (1b) and 3-methoxybenzyne (2) undergo chemoselective palladium-catalyzed [2 + 2 + 2]-cocyclotrimerization with dimethyl acetylenedicarboxylate (DMAD) to afford the corresponding phenanthrenes and/or naphthalenes. The major products are phenanthrenes if Pd(PPh(3))(4) is used as the catalyst, naphthalenes if Pd(2)(dba)(3) is used. When the method is applied to polycyclic arynes