An Efficient Synthesis of 1H-Pyrazolo [3, 4-B]Quinolones Derivatives Catalyzed by MSA in Aqueous Media Under Ultrasound Irradiation

A novel, eco-friendly, and highly efficient method has been developed for the synthesis of 1Hpyrazolo[3,4-b]quinolonederivatives using methanesulfonic acid (MSA) as a catalyst in aqueous medium under ultrasound irradiation. This approach integrates the principles of green chemistry by employing water as a benign solvent and MSA as a biodegradable, non-volatile Brønsted acid catalyst. Ultrasound irradiation significantly accelerates the reaction through acoustic cavitation, leading to enhanced yields and reduced reaction times under mild conditions. The methodology is operationally simple, offers excellent chemoselectivity, and provides good to excellent yields of the desired fused heterocyclic products. The synthesized compounds were thoroughly characterized using IR, ¹H NMR, ¹³C NMR, and mass spectrometry. This protocol represents a sustainable and scalable alternative for the construction of biologically relevant pyrazoloquinolone scaffolds, with potential applications in pharmaceutical and medicinal chemistry.