Diaryl-Pyrazole Phosphine Ligand Design Enables Palladium-Catalyzed Denitrative C–H Arylation of <i>N</i> -Fused Azaheterocycles with Nitroarenes

A newly designed diaryl-pyrazole phosphine ligand, L19, enables an additive-free palladium-catalyzed denitrative C–H arylation of medicinally relevant N-rich azaheterocycles with nitroarenes. Imidazo[1,2-a]azines, triazole, indazole, and caffeine undergo arylation in moderate to excellent yields with high regioselectivity. Mechanistic studies show that the doubly ortho-shielded diaryl-pyrazole framework resists nitrite-mediated oxidation, while isotope-effect experiments indicate that C–H cleavage is not strongly turnover-limiting and comparative DFT supports C–NO2 oxidative addition as the highest-energy step in the modeled productive pathways.