Modular synthesis of PAHs from aryl halides and terminal alkynes via photoinduced palladium catalysis

A visible-light-induced, palladium-catalyzed one-step annulation of aryl halides with terminal alkynes is developed to enable direct access to polycyclic aromatic hydrocarbons (PAHs) under mild conditions. Unlike conventional thermal methods that favor Sonogashira coupling, this transformation proceeds via photoexcitation of Pd(0), generating a Pd(I)/aryl radical hybrid that adds to the alkyne to form a vinyl radical intermediate, enabling regioselective annulation without requiring oxidative addition. The reaction exhibits broad functional group tolerance, wide substrate scope, and excellent scalability, granting modular entry to diverse PAH frameworks, including π-extended and halogenated derivatives. Mechanistic investigations, including radical trapping, radical clock analysis, EPR experiments, light-dependence experiments, and kinetic isotope effect studies, support a radical pathway. This operationally simple and mechanistically distinct approach provides a streamlined and versatile strategy for the construction of functionalized PAHs with potential relevance to materials science and organic electronics.