The construction of aromatic rings by photocatalytic radical-induced cyclization reactions

Abstract

Photocatalytic radical-induced cyclization reactions offer an efficient paradigm for constructing aromatic rings due to their unique environmental friendliness, independence from electronic effects, and high functional group tolerance. However, the high reactivity of intermediates in radical reactions, particularly the challenges of controlling it proceeds in an orderly manner according to the expected pathway and the reaction terminates after the ring is formed, which leads to diminished precision in the construction of aromatic rings. Compared to traditional cyclization methods for synthesizing aromatic rings, photocatalysis enables direct cleavage of high-bond-energy chemical bonds under mild conditions, eliminating the need for high temperature, high pressure, or stoichiometric oxidants. Furthermore, photocatalytic systems can serve as a bridge to connect multiple reaction steps, thereby streamlining the process and enhancing efficiency. Recently, significant progress has been made in applying photocatalytic radical-induced cyclization for the construction of aromatic rings. However, to date, there has been no comprehensive summary of this area reported. In this review, we try to provide a comprehensive perspective on the construction of aromatic rings via photocatalytic radical-induced cyclization. The discussion is organized into five sections based on the type of aromatic ring formed: monoheteroatom-doped aromatic rings, diheteroatom-doped aromatic rings, triheteroatom-doped aromatic rings, all-carbon aromatic ring, and non-classical aromatic rings. This review with a particular focus on elucidating reaction mechanisms, the synergistic effect of catalysts and light sources, and the applications of this strategy in pharmaceutical synthesis and materials science.