Direct Assembly of Angular 5-5-5 Tricyclic Skeletons via a Rh(III)-Catalyzed C-H Activation/Annulation Cascade.

Angular 5-5-5 tricyclic skeletons are privileged yet synthetically challenging motifs due to their high congestion and strain. Herein, we report a Rh(III)-catalyzed cascade annulation of azomethine imines with alkene-tethered vinyl diazo-succinimides, enabling direct access to angular 5-5-5 tricycles in up to 99% yield with excellent regioselectivity under mild reaction conditions. The transformation proceeds through directed C-H activation followed by carbene migratory insertion and an intramolecular [3 + 2] cycloaddition. A broad substrate scope and functional-group tolerance are demonstrated, providing a concise approach to densely fused angular frameworks and expanding the utility of multifunctional diazo reagents in transition-metal-catalyzed cascade synthesis.