Recent advances in the synthesis of indolo[2,1- <i>a</i> ]isoquinolines from <i>N</i> -acryloyl indole derivatives

This review presents a comprehensive overview of recent synthetic strategies for constructing indolo[2,1-<i>a</i>]isoquinoline derivatives from <i>N</i>-acryloyl indole precursors. Particular focus is given to palladium-catalyzed cascade annulations of <i>N</i>-acryloyl-2-(2-halophenyl)indoles, which have enabled diverse functionalizations including carbonylation, borylation, silylation, difluoroalkylation, and thiocarbonylation. These transformations proceed through well-defined Heck-type cyclizations and allow efficient formation of polycyclic frameworks bearing various functional groups. In parallel, the radical cascade cyclization of 2-aryl-<i>N</i>-methylacryloylindoles has emerged as a powerful alternative, with copper, iron, manganese, and photoredox or electrochemical systems enabling selective construction of structurally diverse products under mild conditions. Advances in visible-light photochemistry, catalyst-recyclable protocols, and sustainable radical generation methods have significantly improved functional group compatibility and process efficiency. Collectively, these methodologies offer versatile and practical routes to indolo[2,1-<i>a</i>]isoquinoline scaffolds with promising applications in medicinal chemistry and organic materials.