Novel nano-titania embedded on graphite (nano-TiO2@C-g) as an efficient, eco-friendly, and recyclable catalyst for one-pot, solvent-free synthesis of 4-aryl-3,4-dihydroquinolin-2(1H)-ones, 3-methyl-4-aryl/alkyl-2,4,5,7-tetrahydropyrazolo[3,4-b]pyridin-6-ones, and coumarin-3-carboxylic esters

A novel acid catalyst has been synthesized by commercial anatase phase nano-TiO2 and graphite (nano-TiO2@C-g) via a simple procedure and characterized by Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, thermogravimetric analysis, field emission scanning electron microscopy, and potentiometric titration techniques. It has been utilized as a convenient nano-catalyst to accelerate the one-pot, solvent-free, three-component reaction of Meldrum's acid, aromatic amines (5-methylpyrazol-3-amine), and various aromatic aldehydes to form 4-aryl-3,4-dihydroquinolin-2-(1H)-ones and 3-methyl-4-aryl/alkyl-2,4,5,7-tetrahydropyrazolo[3,4-b]pyridin-6-ones, respectively. The catalytic activity has also examined for the preparation of coumarin-3-carboxylic esters from Meldrum's acid, salicylaldehydes, and alcohols successfully. Low catalyst loading, clean process without utilizing any hazardous solvent, easy workup procedure, reusability and recyclability of the nano-catalyst within four runs without activity loss, high yields of the products, in addition with utilizing a vast range of substrates are some highlighted points of the reported protocols. [GRAPHICS] .