Sc(OTf)₃-Catalyzed Construction of Fused Bisindolylmethanes: Unified Access to 1,2- and 1,7-Linked Indole Frameworks

We report a concise, efficient, and scalable synthetic strategy for the construction of fused bisindolylmethanes (BIMs) via Sc(OTf)₃-catalyzed Friedel-Crafts cyclization of <i>N</i>-alkyl acetal indoles. This protocol enables regioselective access to both 1,2- and previously unexplored 1,7-fused BIMs under mild and operationally simple conditions. The transformation demonstrates broad substrate tolerance and excellent functional group compatibility, delivering structurally diverse fused indole architectures with potential relevance in medicinal chemistry, complex molecule synthesis, and late-stage peptide modification.