A Serendipitous Synthesis: SiO2-HNO3 Mediated Oxidative Aromatization and Regioselective Nitration of 1,3,5-Trisubstituted-4,5-Dihydro-1H-Pyrazoles

Research often leads to unprecedented results that open the gates for new methodologies. We report herein the oxidative aromatization and serendipitous regioselective nitration of 1,3,5-trisubstituted-4,5-dihydro-1H-pyrazoles under mild reaction conditions using SiO2-HNO3 as an oxidizing agent to afford 1,3,5-trisubstituted pyrazoles with high regioselectivity. Here SiO2-HNO3 acts as a nitrating agent along with oxidizing property. SiO2-HNO3 is cheap, easy to prepare, eco-friendly and practically applicable catalyst.