Asish R. Das

Design and synthesis of benzylpyrazolyl coumarin derivatives via a four-component reaction in water: investigation of the weak interactions accumulating in the crystal structure of a signified compound

A combinatorial library of benzylpyrazolyl coumarin derivatives have been synthesized by a green one-pot four-component reaction between aryl hydrazine/hydrazine hydrate (1), ethyl acetoacetate (2), aromatic aldehydes (3) and 4-hydroxycoumarin (4). Molecular scaffolds which assimilate bio-active 3-benzylsubstituted 4-hydroxycoumarins as well as a pyrazolone ring in a single nucleus may be worthwhile molecules from a biological point of view. The reactions were performed in water and employed glacial acetic acid as the right choice of catalyst, and was demonstrated to be the key for rendering the reaction possible and obtained good to excellent yields under reflux conditions within a short period of time. The crystal structures of (R/S)-benzylpyrazolyl coumarin, easily produced by a chromatography-free highly product-selective reaction, were explored by means of single crystal X-ray diffraction analysis and the main intra- and intermolecular interactions perceivable through crystal structure analysis. The presence of a strong intramolecular hydrogen bond was confirmed. In addition, the whole crystal structure consists of other intermolecular hydrogen bonds, such as CH⋯O and aromatic CH⋯π interactions between R- and S-molecules and CH⋯O, NH⋯O and aromatic CH⋯π interactions among only R-molecules and S-molecules in the asymmetric unit.

Magnetically retrievable nano crystalline CuFe2O4 catalyzed multi-component reaction: a facile and efficient synthesis of functionalized dihydropyrano[2,3-c]pyrazole, pyrano[3,2-c]coumarin and 4H-chromene derivatives in aqueous media

CuFe2O4 magnetic nanoparticles were synthesized and recognized as an efficient catalyst for the one-pot synthesis of dihydropyrano[2,3-c]pyrazole, pyrano[3,2-c]coumarin and 4H-chromene derivatives at mild conditions and in excellent yields. The four component reaction (4CRs) of a wide variety of substituted hydrazine derivatives, ethyl acetoacetate, dialkyl acetylenedicarboxylates and alkyl nitrile derivatives (malononitrile and ethyl cyanoacetate) gave the targeted dihydropyrano[2,3-c]pyrazoles. When two equivalents of dialkyl acetylenedicarboxylates were introduced replacing ethyl acetoacetate, a new four-component reaction took place providing another type of dihydropyrano[2,3-c]pyrazole derivatives. An efficient and practical route to pyrano[3,2-c]coumarin and 4H-chromene framework has also been developed by one-pot, three-component reaction (3CRs) of 4-hydroxycoumarin/dimedone/cyclohexane-1,3-dione, dialkyl acetylenedicarboxylates and alkyl nitriles. CuFe2O4 magnetic nanoparticles were prepared by a simple and effective citric acid complex method and characterized by using XRD, FT-IR, EDX and TEM image. The catalyst was recycled for six cycles with almost unaltered catalytic activity. All reactions were easily performed and proceeded with high efficiency under very simple and mild conditions and gave excellent yields avoiding time-consuming, costly syntheses, and tedious workup and purification of products.

In situ synthesis of a reduced graphene oxide/cuprous oxide nanocomposite: a reusable catalyst

A reduced graphene oxide/cuprous oxide (RGO/Cu2O) nanocomposite has been successfully synthesized applying a simple in situ reduction method using an aqueous solution of lactulose which is used simultaneously as a reducing and stabilizing agent. Lactulose, a disaccharide, has the ability to reduce both GO and CuSO4 in situ under alkaline conditions. The GO and RGO/Cu2O nanocomposites are characterized using transmission electron microscopy, energy dispersive X-ray spectroscopy, field emission scanning electron spectroscopy, X-ray diffraction, Fourier-transform infrared spectroscopy and UV-vis absorption spectroscopy. The surface charge as well as stability is established by analyzing the zeta potential value. The results confirm the synthesis of the RGO/Cu2O nanocomposite and the existence of interactions between Cu2O and RGO. It is also observed that Cu2O nanoparticles with an average size of 5 nm are uniformly dispersed throughout the RGO sheets. The catalytic activity of the RGO/Cu2O nanocomposite is excellent for the ‘click’ reaction and remains the same for six cycles.

Three-component synthesis of a polysubstituted pyrrole core containing heterocyclic scaffolds over magnetically separable nanocrystalline copper ferrite

A highly convergent, efficient and practical heteroannulation protocol for the synthesis of a library of coumarin and uracil fused pyrrole derivatives has been developed. Reactions involving the CuFe2O4 catalyzed one-pot three-component domino coupling of 6-aminouracil/4-aminocoumarin, aldehydes and nitromethane resulted in highly substituted coumarin and uracil fused pyrrole derivatives, making this strategy very useful in diversity-oriented synthesis (DOS). CuFe2O4 magnetic nanoparticles were prepared by a simple and effective citric acid complex method and characterized by using XRD, FT-IR, and TEM images. The easy recovery of the catalyst and high yield of the products makes the protocol attractive, sustainable and economic. The catalyst was recycled for six cycles with almost unaltered catalytic activity.

A new application of polymer supported, homogeneous and reusable catalyst PEG–SO3H in the synthesis of coumarin and uracil fused pyrrole derivatives

A highly efficient, simple and convenient synthetic protocol for the synthesis of coumarin and uracil fused pyrrole derivatives has been demonstrated. A biodegradable, polymer supported catalyst, PEG–SO3H, was applied for the two component coupling of 4-aminocoumarin or 6-aminouracil and α,β-unsaturated nitroalkene. The catalyst has efficiently catalyzed the Michael addition and intramolecular cyclisation with the concomitant removal of the nitro group. The catalyst was recycled for five cycles with almost unaltered catalytic activity.

Triton-X-100 catalyzed synthesis of 1,4-dihydropyridines and their aromatization to pyridines and a new one pot synthesis of pyridines using visible light in aqueous media

A realistic and convenient synthetic method has been developed for the facile synthesis of 1,4-dihydropyridine derivatives in the presence of the non-ionic surfactant Triton X-100, in an aqueous medium at room temperature. A greener method to synthesize pyridine derivatives has also been developed by the oxidation of 1,4-dihydropyridine derivatives with almost 100% yields and also in a one pot synthesis, employing an aldehyde, ethyl acetoacetate and ammonium acetate in an aqueous micellar medium by irradiation with potassium persulphate in the presence of visible light. The one pot protocol offered excellent yields of the targeted product in a very short period of time at room temperature and the non-ionic surfactant catalyst can be recovered very easily. We also observed that during the reaction there was the formation of micelles, or micelle-like colloidal aggregates, from the non-ionic surfactant and the reaction mixture in water, measured by dynamic light scattering and visualized through an optical microscope. The process is advantageous as ammonia is generated from an ammonium salt under absolutely neutral conditions and the product purification follows a group assistant purification chemistry process (GAP).

Synthesis of 2,3-dihydroquinazolinones and quinazolin-4(3H)-ones catalyzed by graphene oxide nanosheets in an aqueous medium: “on-water” synthesis accompanied by carbocatalysis and selective C–C bond cleavage

Graphene oxide (GO) nanosheet catalyzed new and straightforward strategies for the construction of 2,3-dihydroquinazolinones and quinazolin-4(3H)-ones starting from anthranilamide (2-aminobenzamide) and an aldehyde/ketone in aqueous medium at room temperature have been realized. This catalyst is also found to be efficient for the expedient construction of quinazolin-4(3H)-ones starting from anthranilamide and a β-ketoester/1,3-diketone following selective C–C bond cleavage of the β-ketoester/1,3-diketone at an elevated temperature under metal and oxidant free conditions.

PhIO promoted synthesis of nitrile imines and nitrile oxides within a micellar core in aqueous media: a regiocontrolled approach to synthesizing densely functionalized pyrazole and isoxazoline derivatives

A highly efficient and general protocol has been developed for the facile synthesis of highly diversified 1,3,5-trisubstituted pyrazoles and 3,5-disubstituted 2-isoxazolines through one-pot tandem intermolecular, as well as intramolecular, dipolar [3 + 2] cycloaddition reactions. Chemoselective oxidation of aldohydrazone to nitrile imine and aldoximes to nitrile oxides by iodosobenzene in neutral aqueous media was performed. The scope of the reactions in regiocontrolled dipolar cycloaddition with olefins in the presence of PhIO toward highly substituted pyrazole and isoxazoline derivatives has been demonstrated. SDS converted the initially floating reaction mass and the organo-oxidant PhIO into a homogeneous mixture, which on stirring became a turbid emulsion. The micellar arrangement was confirmed by dynamic light scattering and optical microscopy. The new, green and metal free synthetic method enabled the execution of regiocontrolled tandem cycloaddition oxidation sequences leading to a library of pyrazole and isoxazoline derivatives.

Facile synthesis of pyridopyrimidine and coumarin fused pyridine libraries over a Lewis base-surfactant-combined catalyst TEOA in aqueous medium

A highly convergent and efficient protocol, for the facile synthesis of a library of coumarin fused pyridine and pyridopyrimidine derivatives, has been developed by applying a Lewis base-surfactant-combined catalyst (LBSC) triethanolamine (TEOA). The method described has the benefits of operational simplicity and excellent yields of the targeted molecule. The LBSCs were found to form stable colloidal dispersions rapidly in the presence of reaction substrates in water, even when the substrates are solid. In light of the increased demand for reduction of organic solvents in industry, the surfactant aided Lewis base catalysis described here may have immense practical consequences in organic synthesis. This work may not only lead to environmentally benign systems but also will provide a newer aspect of organic chemistry in water.

A facile and efficient synthesis of functionalized 4-oxo-2-(phenylimino)thiazolidin-5-ylideneacetate derivatives via a CuFe2O4 magnetic nanoparticles catalyzed regioselective pathway

Nano-CuFe2O4 spinel has been found to exhibit strong catalytic activity in the cascade reaction involving 1,4-addition and intramolecular electrophilic cyclization in a perfectly regiocontrolled manner and a series of functionalized 4-oxo-2-(phenylimino)thiazolidin-5-ylideneacetate derivatives were generated successfully. The reaction is mild and selective with good to high yields and displays significant functional group tolerance. The dual role of the thiocarbonyl moiety as an electrophile and as a nucleophile has been observed in this three component coupling reaction. CuFe2O4 magnetic nanoparticles were prepared by a simple and effective citric acid complex method and characterized by using XRD, FT-IR, and TEM analysis. The catalyst was recycled for six cycles without any loss of catalytic activity. All reactions were easily performed and proceeded with high efficiency under very simple and mild conditions and gave excellent yields avoiding time-consuming, costly syntheses, tedious workup and purification hazards.