Scalable Synthesis of Seven-Membered 3,4-Fused Tricyclic Indole Scaffolds Enabling Conformationally Fixed Aminobenzosuberene Analogues

We report an improved and scalable synthetic route to seven-membered 3,4-fused tricyclic indole scaffolds, providing practical access to the target framework with good overall efficiency and reproducibility. A key feature is Sc(OTf)3-promoted regioselective Fischer indolization of ortho-substituted phenylhydrazone 5b, which overrides the anomalous pathway observed under conventional acidic conditions. The synthetic utility of the scaffold was demonstrated through the preparation of aminobenzosuberene-inspired derivatives. Preliminary biological evaluation revealed that compound 1b exhibited antimitotic activity at 0.2 μM.