Light‐Driven [2 + 2] Cycloaddition Strategies for the Synthesis of Cyclobuta[ b ]indoles and Their Derivatives

The dearomatization of indoles is a powerful strategy for transforming simple substrates into architecturally complex molecular frameworks. This review provides a comprehensive overview of photoinduced methodologies developed for the construction of three‐dimensional polycyclic systems bearing indolyl‐cyclobutane motifs. We summarize classical ultraviolet(‐driven [2 + 2] cycloaddition reactions alongside recent advances in photocatalysis, including sensitizer‐ or photocatalyst‐mediated energy‐transfer and single‐electron transfer processes. Attention is also given to photoinduced hetero‐[2 + 2] cycloadditions, specifically the Büchi and aza‐Büchi reactions, as well as photodimerization pathways of indole derivatives. Together, these approaches provide valuable and versatile tools for the rapid assembly of complex molecular architectures and drug‐like scaffolds.