Dihydropyrimidin-2(1H)ones(thiones) (DHPM) and coumarin-3-carboxylic acid are obtained in excellent to good yield by employing green catalyst under solvent-free condition. The condensation of substituted arylaldehyde, 1,3-diketoester and urea/thiourea in the presence of green catalyst after 1 h of stirring at 50C resulted in DHPM. The reaction of substituted o-hydroxybenzaldehyde with Meldrum's acid in the presence of catalyst under sonication for a few minutes gave coumarin-3-carboxylic acid.

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... Here, we have used Lewis acid catalyst RHA-SiO2(NPs)-BO3H3 derived from the agro-waste of rice husk, a heterogeneous catalyst for important organic scaffold synthesis. The reaction required low catalyst loading (1.2 mg) to achieve a target product under solvent-free condition. A series of other derivatives of heterogeneous catalysts synthesized are RHA-SiO2, RHA-SiO2(NPs), RHA-SiO2-BO3H3. We examined their catalytic activity in the synthesis of DHPM and coumarin-3-carboxylic acid. Only the reaction catalysed by RHA-SiO2(NPs)-BO3H3 gave excellent yield of the product. The final isolated pure product has been fully characterized by various spectroscopic methods and confirmed.