A simple, practical, and economical protocol for the synthesis of a series of twelve 2-amino-5-oxo-4-aryl-5H-chromeno[4,3-b]pyridin-3-yl cyanides have been developed by the cyclocondensation reaction of 4-aminocoumarin, aromatic aldehydes, and malononirile in the presence of cadmium oxide nanoparticles (CdO NPs) as an cost-effective, reusable, and highly efficient heterogeneous catalyst in aqueous medium at 60 °C. The procedure is very simple, clean, mild, and practical for aromatic, as well as heteroaromatic, aldehydes without significant difference.

A solvent-free condensation between aromatic aldehydes, ammonium acetate and active methylene compounds comprising dimedone or 1,3-indanedione, in the presence of CuI nanoparticles as an efficient and recyclable catalyst leads to the formation of 4-arylacridinediones and 6-aryldiindeno[1,2-b:2,1-e]pyridinediones. This novel and practical approach has a number of advantages for instance, the condensation itself is solvent-free, the total amount of solvent used in the whole process is significantly decreased, the yields of pure products are high to excellent without any by-products, the catalyst is reusable, and the work-up is very simple.

Aim and Objective: In the last decades, it has been extensively verified that nanostructured transition metal oxides emerge as inexpensive, available and extremely efficient heterogeneous catalysts in chemical transformations. The high electrical conductivity, high carrier concentration, and improved reactivity in cadmium oxide nanoparticles (CdO NPs) make it as a potential candidate for applications in the fields of nanocatalysis. [1]Benzopyran and pyridopyrimidine derivatives compose major classes of heterocyclic compounds, which have a wide spectrum of biologically activities. Materials and Methods: In the present work we report a facile and highly effective synthesis of 8-aryl-8H-[1,3]dioxolo[4,5- g][1]benzopyran-6-carboxylic acids and 1,3-dimethyl-2,4-dioxo-5-phenyl-1,2,3,4,5,8-hexahydropyrido[2,3-d]pyrimidine-7- carboxylic acids via CdO NPs catalyzed cyclocondensation reaction of 4-substituted phenylmethylidenepyruvic acids with 3,4- methylenedioxyphenol or 1,3-dimethylbarbituric acid which was accomplished under ethanol-drop grinding at room temperature. The described catalyst was prepared successfully by a simple precipitation method and characterized by the Fourier transformed infrared absorption (FT-IR) spectroscopy, X-Ray diffraction (XRD) analytical technique, and scanning electron microscopy (SEM). Results: A number of [1,3]dioxolo[g][1]benzopyran-6-carboxylic acids and pyrido[d]pyrimidine-7-carboxylic acids were effectively synthesized in high yields (96-98%) within short reaction times (10-15 min). All synthesized compounds were well characterized by IR, 1H and 13C NMR spectroscopy, and also by elemental analyses. Conclusion: In summary, we have developed a very simple and impressive procedure for the synthesis of 8-aryl-8H- [1,3]dioxolo[4,5-g][1]benzopyran-6-carboxylic acids and 1,3-dimethyl-2,4-dioxo-5-phenyl-1,2,3,4,5,8-hexahydropyrido[2,3- d]pyrimidine-7-carboxylic acids as biologically interesting structures in the presence of CdO NPs as an efficient recyclable heterogeneous catalyst. The remarkable advantages for the offered protocol compared with traditional methods are short reaction time, good yields of the products, and the ease of operation with simple work-up procedure.

In this study, copper chromite nanoparticles (CuCr 2 O 4 NPs) were prepared by a simple hydrothermal method. This nanomaterial was found as an efficient heterogeneous catalyst for the synthesis of a new class of [1]benzopyran azo dyes via pseudo-three-component reaction of (E)-1,2-diphenyl-1-diazene with 4-hydroxycoumarin in the ratio 1:2. The aim of the present work was to provide a practical and high yielding protocol that offers several advantages such as simple procedure with an easy work-up, mild reaction conditions, and the use of CuCr 2 O 4 NPs as an efficient and easily recoverable catalyst.

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