1-Methylimidazolium tricyanomethanide {[HMIM]C(CN)3} as a nano structure and reusable molten salt catalyst for the synthesis of tetrahydrobenzo[b]pyrans via tandem Knoevenagel-Michael cyclocondensation and 3,4-dihydropyrano[c]chromene derivatives

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.

Captopril supported on magnetic graphene nitride, a sustainable and green catalyst for one-pot multicomponent synthesis of 2-amino-4H-chromene and 1,2,3,6-tetrahydropyrimidine

Captopril (CAP) is a safe, cost-effective, and environmentally organic compound that can be used as an effective organo-catalyst. Functional groups of captopril make it capable to attach to solid support and acting as promoters in organic transformations. In this work, captopril was attached to the surface of magnetic graphene nitride by employing a linker agent. The synthesized composite efficiently catalyzed two multicomponent reactions including the synthesis of 1,2,3,6-tetrahydropyrimidine and 2-amino-4H-chromene derivatives. A large library of functional targeted products was synthesized in mild reaction conditions. More importantly, this catalyst was stable and magnetically recycled and reused for at least five runs without losing catalytic activity.

Synthesis and characterization of Fe3O4@Sal@Cu as a novel, efficient and heterogeneous catalyst and its application in the synthesis of 2-amino-4H-chromenes

This research paper presents the synthesis and characterization of the magnetic nanoparticle, Fe₃O₄@Sal@Cu, [Fe₃O₄@Si-CH₂-CH₂-CH₂-NH-NH-CO-N=CH-(2-HO-C₆H₄-)@Cu] as a green and retrievable catalyst. This catalyst was characterized by FTIR, XRD, EDX and TGA analyses. In addition, the catalytic activity of this new catalyst was investigated for the synthesis of 2-amino 4H-chromenes by producing good-to-excellent yields under mild reaction conditions. The other advantages of the developed nanocatalyst are its ecofriendliness, being easy to handle, high reusability and being magnetically separable. The synthesis of some new derivatives of 2-amino-4H-chromenes in the presence of this nanocatalyst is also reported.

Cysteic acid grafted to magnetic graphene oxide as a promising recoverable solid acid catalyst for the synthesis of diverse 4H-chromene

4H-chromenes play a significant role in natural and pharmacological products. Despite continuous advances in the synthesis methodology of these compounds, there is still a lack of a green and efficient method. In this study, we have designed cysteic acid chemically attached to magnetic graphene oxide (MNPs·GO-CysA) as an efficient and reusable solid acid catalyst to synthesize 4H-chromene skeletons via a one-pot three components reaction of an enolizable compound, malononitrile, an aldehyde or isatin, and a mixture of water-ethanol as a green solvent. This new heterogeneous catalyst provides desired products with a good to excellent yield, short time, and mild condition. This procedure presents an environmentally friendly approach for the synthesis of a great number of 4H-chromene derivatives.

Synthesis of Core-Shell Magnetic Supramolecular Nanocatalysts based on Amino-Functionalized Calix[4]arenes for the Synthesis of 4H-Chromenes by Ultrasonic Waves

One of the most common phenol-formaldehyde cyclic oligomers from hydroxyalkylation reactions that exhibit supramolecular chemistry are calixarenes. These macrocyclic compounds are qualified to act as synthetic catalysts due to their specific features including being able to form host-guest complexes, having unique structural scaffolds and their relative ease of chemical modifications with a variety of functions on their upper rim and lower rim. Here, a functional magnetic nanocatalyst was designed and synthesized by using a synthetic amino-functionalized calix[4]arene. Its catalytic activity was evaluated in a one-pot synthesis of 2-amino-4H-chromene derivatives. Besides, this novel magnetic nanocatalyst was characterized by spectroscopic and analytical techniques such as FT-IR, EDX, FE-SEM, TEM VSM, XRD analysis.

One Pot Synthesis of Biscoumarins and Pyranocoumarins by Coconut Juice as a Natural Catalyst

Background:

The conception of ‘Green chemistry’ is the much inventive chemistry which is potent and more environmentally benign. It is notable that many organic reactions take place in conventional organic solvents, known as volatile organic compounds. Being concerned about the environmental impact, we report a promoting medium, coconut juice (ACC) for one-pot synthesis of biscoumarins and pyranocoumarins which is safe, harmless, green and environmentally benign.

Methods and Results:

Substituted biscoumarins have been achieved by the reaction of biscoumarin and substituted aromatic aldehydes in presence of ACC which acts as a green catalyst cum solvent. Each reaction showed good to excellent yield in presence of both electron donating as well as electron withdrawing group on aromatic aldehyde without formation of any by-products. Similarly, pyranocoumarins have been achieved by the reaction of biscoumarin, substituted aromatic aldehydes, active methylene nitrile in presence of ACC. All the reactions proceed smoothly and gave higher yields in case of malononitrile in comparison of ethyl-2-cyanoacetate.

Conclusion:

A simple, eco-friendly and novel procedure was demonstrated for the synthesis of biscoumarins and pyranocoumarins using natural feedstock coconut juice. The major importance of using ACC juice is higher yields, no work-up and no column chromatography.

The molecular diversity scope of 4-hydroxycoumarin in the synthesis of heterocyclic compounds via multicomponent reactions

4-Hydroxycoumarins are some of the most versatile heterocyclic scaffolds and are frequently applied in the synthesis of various organic compounds. 4-Hydroxycoumarin-based compounds are important among heterocyclic structures due to their biological and pharmaceutical activities. In this study, we provide an overview on the recent applications of 4-hydroxycoumarin in multicomponent reactions for the synthesis of various heterocyclic compounds during the time period of 2015-2018.