Synthesis of Functionalized Pyrazoles via Vanadium-Catalyzed C–N Dehydrogenative Cross-Coupling and Fluorescence Switch-On Sensing of BSA Protein

Vanadium-catalyzed C–N dehydrogenative cross-coupling of alkenyl hydrazones leading to functionalized pyrazoles is described in a 1:1 mixture of toluene/H₂O using air as the terminal oxidant. Significant practical features include use of the commercial nontoxic VOSO₄ as a recyclable catalyst, mild reaction conditions, scalability, and the broad substrate scope. Some of the product pyrazoles exhibit interesting photophysical properties. Fluorescence light-up sensing of BSA protein by one of the pyrazoles is also highlighted.