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.