Many natural products and pharmaceuticals with a broad range of biological activities constitute one or other heterocyclic scaffolds. In pursuit of new synthetic methodologies for diverse heterocyclic compounds, the Multicomponent Reaction (MCR) is an advanced strategy to develop and design versatile organic molecules with high atom economy in a short period. Major advantages of MCRs is the reaction takes place in a one-pot strategy with no need for the separation and purification of intermediates. The synthesis of diverse heterocyclic scaffolds using the MCR strategy can be achieved, and is on the increase. Green Chemistry is an emerging branch of synthetic chemistry, which is to design sustainable synthetic protocols from easily available starting materials and non-corrosive solvents. One fundamental aspect of green chemistry is the reusability of materials and reducing waste. This allows chemists to consider heterogeneous catalysis in reactions because it is easy to separate from the reaction mixture and is reusable. Ease in handling, greater chemo-regio selectivity, and thermal stability are the added advantages of heterogeneous catalysis. Heterogeneous catalysis using mixed metal oxides is gaining importance due to the tuning of surface properties of materials, i.e., one is able to design the catalyst as per requirement by loading/doping of necessary metals on supports. Among many support materials, zirconia gained prominence due to its higher surface area and amphoteric surface properties, which make it an ideal catalytic support. Having a high surface area is advantageous for a reaction to takes place on the surface, which provides necessary active sites to accelerate the reaction. This research was designed to synthesize various novel core N-heterocyclic moieties by using zirconia-supported mixed metal oxide catalysts. During the study, an attempt was made to develop fast reaction protocols to synthesize various pyridine, pyrimidine and pyrazole derivatives with excellent yields using green solvents and mild conditions. These new protocols demonstrated efficacy and high selectivity under eco-friendly conditions. The following six series of reactions were studied: 1. Synthesis of eleven novel functionalized 1,4-dihydropyridine derivatives by using V2O5/ZrO2 as catalyst for the multicomponent reaction using various aromatic aldehydes, 5,5-dimethyl-1,3-cyclohexanedione, acetoacetanilide and ammonium acetate. 2. A one-pot protocol to synthesize novel functionalized halopyridine derivatives by using RuO2/ZrO2 as an efficient reusable catalyst for the condensation of aromatic aldehydes, malononitrile, diethyl acetylene dicarboxylate and 3-chloro-4-fluoroaniline under green conditions. 3. A room-temperature synthesis of 2,4-dihydropyrano[2,3-c]pyrazole-3-carboxylates by the condensation of aromatic aldehydes, malononitrile, hydrazine hydrate and diethyl acetylene- dicarboxylate using Bi2O3/ZrO2 as a cost-effective catalyst with ethanol as a greener solvent. 4. Greener synthesis of indenopyrimidine derivatives by using Ag2O on ZrO2 as a recyclable catalyst for the one-pot condensation between an aromatic aldehyde, 1,3-indanedione and guanidinium hydrochloride at room temperature. 5. Synthesis of new 1,4-dihydropyridine derivatives via cyclo-condensation between an aromatic aldehyde, 1,3-cyclohexanedione, acetoacetanilide and ammonium acetate in an one-pot strategy through a green protocol using Fe2O3/ZrO2 as a reusable catalyst at room temperature. 6. A four-component fusion protocol for the synthesis of novel 1,4-dihydropyridine derivatives by the one-pot condensation between substituted aldehydes, ethyl acetoacetate,1,3-cyclohexadione/5,5-dimethyl-1,3-cyclohexanedione and ammonium acetate in ethanol. All the prepared catalytic materials were characterized by PXRD, TEM, SEM, Pyridine-IR and BET surface area analysis. All the synthesized organic compounds were characterized and confirmed by 1H NMR, 15N NMR, 13C NMR, FT-IR, single-crystal XRD, and HRMS. Advantages offered by these protocols are environmentally-friendly simple procedure, mild conditions and short reaction times with excellent yields.

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