Cyclization Synthetic Methodologies for Triphenylene Derivatives

Triphenylene frameworks, privileged pericondensed polyarenes, are foundational in optoelectronics, bioactives, and supramolecular engineering. The efficient synthesis of triphenylene-based polycyclic aromatic hydrocarbons (PAHs) faces longstanding challenges due to inherent limitations in conventional methodologies, including cycloadditions, oxidative dehydrogenation, and transition metal-coupling reactions. These approaches frequently require stringent reaction conditions, exhibit inadequate regioselectivity, and demonstrate limited functional group tolerance. While transition metal-catalyzed C─H activation strategies have markedly improved synthetic efficiency and selectivity, the advancement remains constrained by dependence on precious metals and significant scalability issues. Contemporary precision synthesis approaches, integrating green chemistry principles, photocatalysis, and electrosynthesis, now enable efficient bond formation with exquisite regiocontrol under mild conditions. This evolution is steering PAH synthesis toward sustainable and operationally efficient paradigms. This review systematically reviews recent progress in triphenylene synthesis, highlighting in particular recent advances in palladium-catalyzed C─H activation and radical-mediated photoredox cascade methodologies. It examines the regiochemical factors controlling ring formation, alongside synthetic applications, current limitations, and reaction mechanisms in representative cascade transformations to provide insights for the synthesis development prospects of triphenylenes.