Metal-Catalyzed Benzannulation: Recent Advances in Catalyst Design, Mechanistic Insights, and Aromatic Framework...

Benzannulation is a key transformation in organic synthesis, enabling direct access to aromatic and heteroaromatic scaffolds central to natural products, pharmaceuticals, agrochemicals, dyes, electronic devices, and materials. The construction of these frameworks continues to pose a challenge because it requires high regioselectivity, broad substrate scope, and functional-group tolerance. Traditional multistep approaches often suffer from limited efficiency, highlighting the need for more versatile synthetic strategies. Metal-catalyzed benzannulation has emerged as an effective solution, offering excellent efficiency, high selectivity, and broad synthetic applicability. Catalysts based on transition metals (Sc, Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Ir, and Au), together with main-group, post-transition, and rare-earth metals (Ca, Al, In, Bi, La, and Yb), have expanded the scope of these transformations. Despite these advances, a comprehensive understanding of catalyst design, reaction mechanisms, and synthetic applications remains incomplete, underscoring the need for an up-to-date and systematic overview. This review addresses this need by providing an overview of metal-catalyzed benzannulation reported since 2018, with particular emphasis on catalyst design, mechanistic insights, and synthetic applications. By integrating recent advances across diverse metal-catalyzed systems, this review provides a comprehensive perspective on the field and offers guidance for the future development of efficient and selective benzannulation methodologies.