Palladium-Catalyzed Intermolecular Decarboxylative Coupling of 2-Phenylbenzoic Acids with Alkynes via C−H and C−C Bond Activation

A novel protocol for palladium-catalyzed intermolecular formal [4 + 2] annulation of 2-phenylbenzoic acids with alkynes is described. Acridine is shown to be essential for the high reaction efficiency. Phenanthrene derivatives are formed in moderate to good yields without coupling (pseudo)halides or organometallic species.