Efficient One-Pot Synthesis of 4-(((8-Hydroxyquinolin-7-yl) (phenyl) methyl)amino)-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one Derivatives Using TiO ₂ Nanoparticles as a Catalyst

A series of 4-(((8-hydroxyquinolin-7-yl)(phenyl)methyl)amino)-1,5-dimethyl-2-phenyl- 1,2-dihydro-3H-pyrazol-3-one derivatives (4a–j) were synthesized via a one-pot, three-component reaction. The reaction employed benzaldehyde derivatives (1a–j), 4-aminoantipyrine (2), and 8- hydroxyquinoline (3), using titanium dioxide nanoparticles (TiO<sub>2</sub> NPs) as a catalyst. The TiO<sub>2</sub> NPs, synthesized through a sol–gel method, efficiently catalyzed the transformation under mild conditions, delivering high yields in just 9 minutes at room temperature. Optimization revealed that 0.010 g of catalyst in methanol was optimal, with protic solvents outperforming aprotic and non-polar ones. The reaction progress was monitored using thin-layer chromatography (TLC), and the final products were isolated via recrystallization. A systematic study of reaction parameters confirmed TiO<sub>2</sub> NPs as an efficient, reusable, and environmentally friendly catalyst for multicomponent organic synthesis.