Aqua one-pot, three-component synthesis of dihydropyrano[3,2-c]chromenes and amino-benzochromenes catalyzed by sodium malonate

Ni-Unsymmetrical Salen Complex-Catalyzed One-Pot Multicomponent Reactions for Efficient Synthesis of Biologically Active 2-Amino-3-cyano-4H-pyrans

In this report, four new Ni(II)-unsymmetrical salen complexes, [NiL1-4], were prepared by refluxing Ni(Ac)2·4H2O with unsymmetrical salen ligands, H2L1-4. All of the synthesized ligands and complexes were characterized by various physicochemical methods. Also, the solid-state structures of [NiL1], [NiL2], and [NiL4] were defined through single-crystal X-ray diffraction methods. The catalytic potential of [NiL1-4] was investigated by economic and environmentally friendly one-pot-three-component reactions (using reagent: 1,3-dicarbonyls, malononitrile, benzaldehyde, or its derivatives) for the synthesis of biologically active 2-amino-3-cyano-4H-pyran derivatives (total 16 derivatives). After optimization of the reaction conditions, this new synthetic protocol by taking Ni(II)-unsymmetrical salen complexes as catalysts shows excellent conversion with a maximum yield of up to 98% of the effective catalytic products within 1 h of reaction time. In addition, it was observed that the aromatic aldehyde containing an electron-withdrawing group as a ring substituent shows better conversion (up to 98%), and the electron-donating group substituent shows similar or less conversion compared to benzaldehyde under the optimized reaction conditions. From the comparison of results between all these Ni complexes, it was found that the efficiency of the catalytic performance follows the order [NiL1] > [NiL3] > [NiL2] > [NiL4]. A possible reaction pathway was predicted and established through UV-vis spectroscopy. Intermediate II proposed in the reaction pathway was also trapped and characterized through 1H and 13C NMR.

One-Pot Synthesis of 4H-Pyrano[3,2-c]coumarin Derivatives Catalyzed by Deep Eutectic Solvent

4H-Pyrano[3,2-c]coumarin derivatives are an important class of pharmaceutical compounds that are expensive to prepare by previously reported methods. An efficient and green method was developed to obtain these derivatives using the deep eutectic solvent (DES) zinc chloride/acetamide (n:n = 1:4), which acted as both the catalyst and the solvent for the reaction. An aromatic aldehyde, 4-hydroxycoumarin, and cyanoacetate were used as the substrates. The DES, substrate molar ratio, diluent type, temperature, and reaction time were optimized to obtain the 4H-pyrano[3,2-c]coumarin derivatives from a range of aromatic aldehydes in a single step in moderate to high yields and under mild reaction conditions.