Skeletal Rearrangement of Biaryls via Rhodium-Azirine Intermediate: A Route to Solid-State Emissive Polycyclic...

We report a rhodium-catalyzed cascade transformation of biaryl alkynylsulfamates that enables access to rigid, spirocyclic cycloheptatrienes with strong solid-state fluorescence. Building on prior work confirming selective 7-endo nitrene-alkyne cyclization, our design leverages skeletal rigidity to promote a thermally driven electrocyclic ring opening. Detailed mechanistic studies, supported by density functional theory (DFT) calculations, reveal a key rhodium-bound azirine intermediate that undergoes a dearomative single-carbon insertion into the biaryl framework. This reaction proceeds via a distinct, noncarbene-based pathway, expanding the scope of nitrene-mediated rearrangements beyond classical Büchner-type mechanisms. The method provides a modular route to structurally complex and photoactive scaffolds through rationally designed cascade processes.