Harnessing pyridinium ylides for ionic cascades provides a scalable mechanochemical route to azaindazoles and related heterocycles

Here, we report a mechanochemical strategy that directly functionalizes C–H bonds in pyridines, quinolines, isoquinolines, and quinoxalines to access fused azaheterocycles. Readily generated ylides react with aryl diazonium tetrafluoroborates through an ionic cascade comprising nucleophilic substitution, intramolecular S N Ar, electrocyclization, and rearomatization to deliver N -aryl-7-azaindazoles, pyrazoloquinolines, pyrazoloisoquinolines, and pyrazoloquinoxalines with excellent regioselectivity. The method is metal free, operationally simple, and sustainable, enabling the preparation of 51 distinct analogs with broad substrate scope. We demonstrate its utility through late-stage diversification of drug molecules and representative derivatizations, including regioisomeric azaindazole formation and Pd-catalyzed C–N coupling. Mechanistic experiments support an ionic cascade pathway. Notably, the protocol translates efficiently to DYNO-MILL bead-milling conditions, highlighting its potential for scalable, industrial, solvent-free synthesis.