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Multi-metallic hybrid nancatalysts consisting of a porous metal oxide host and metal satellite guests serve as a scaffold for multi-step transformations of divergent and energy-challenging substrates. Here we have developed a 3D porous MgO framework (Lewis basic host) with Ag(0) nanoparticles (noble metal guest) for ambient pressure activation and insertion of CO(2) into unsaturated alkyne substrates. The hybrid MgO@Ag-x (x = 2, 5, 7, 8 at % Ag) catalysts are synthesized by impregnating Ag(+) ions in porous MgO cubes followed by reduction using NaBH(4). Morphological (SEM, TEM, EDX mapping) and structural (PXRD, XPS) characterization reveal that the micron-sized hybrid cubes derive from self-assembly of ~100 nm (edge length) MgO cubes decorated with ~ 5 to 25 nm Ag(0) NPs. Detailed XPS analysis illustrates Ag(0) is present in two forms

A green approach for decarboxylative C(sp3)–H activation of proline amino acid was accomplished by coupling with aldehydes and alkynes to afford α-alkynylated N-substituted pyrrolidines as value-added synthons using reduced graphene oxide supported copper oxide (RGO@CuO) nanocatalysts. The RGO@CuO nanocomposites were obtained by the impregnation of micrometer-sized malachite spheres, as a renewable and sustainable copper mineral precursor, on the graphene oxide (GO) sheets followed by calcination at 300–450 °C for 5 h. The characterization of as-synthesized composites revealed the generation of monodispersed and uniformly embedded copper oxide (CuO) nanoparticles with sizes ranging from 10 to 15 nm on RGO thin sheets via GO as a support as well as indirect template for dissembling and decomposition of micrometer-sized malachite spheres. The RGO@CuO composites were found to be efficient and robust nanocatalysts compared with CuO nanoparticles (NPs) alone. The present method offers several advantages, such ...

Development of nanocatalysts for a chemical reaction with ideal values in green chemistry metrics is considered to be a challenging task to achieve sustainable chemistry. With this aim, we herein report a hierarchically porous sphere-like copper oxide (HS-CuO) nanocatalyst to afford benzofuranamine and dihydro-benzofuranamine isomers with anomalous selectivity via O-annulated A3 coupling among salicylaldehydes, secondary amines, and alkynes followed by cycloisomerization in the absence of base and solvent. The anomalous selectivity of benzofuran isomers was dependent on the electronic factors of substituents on salicylaldehyde and the type of secondary amines used in the coupling reaction. The HS-CuO nanocatalyst was recycled five times without significant loss in its catalytic activity. The present method offers several advantages over the reported methods such as wide substrate scope with anomalous selectivity in the products, high yields in short reaction time, avoided the usage of extra reagents such ...

An environmentally benign and surfactant-free method was developed for the preparation of porous silica nanospheres (SiO2 NS) from the hydrolysis of tetraethoxyorthosilicate (TEOS), using corn starch as a sacrificial template. The stabilization of malachite on SiO2 NS, followed by calcination at 600 °C, afforded silica-nanosphere-embedded copper oxide (Cu@SiO2-NS). The obtained Cu@SiO2-NS was found to be a versatile nanocatalyst for the decarboxylative coupling strategies to afford aromatic or aliphatic N-heterocycles such as aminoindolozines, pyrrolo[1,2-a]quinolones, and substituted pyrrolidine. The Cu@SiO2-NS was successfully recycled for six times without significant loss in its catalytic efficiency. The present method shows several advantages, such as being an environmentally benign approach for the catalyst preparation, being easy to handle, and having a wide substrate scope for decarboxylative couplings with excellent yields in short reaction time, and showed excellent green chemistry metrics, such...

C1-Alkynylation of tetrahydroisoquinoline (THIQ) was achieved via the A3 coupling strategy from the reaction of THIQ as a secondary amine, aldehydes and alkynes using the CuO@Fe2O3 nanocatalyst under green reaction conditions. The wide scope of the present method was studied using various aliphatic/aromatic aldehydes and alkynes to afford the corresponding C1-alkynylated products in quantitative yields. Moreover, the present catalytic system was found to be versatile for the decarboxylative A3 coupling strategy with improved progress of reactions by replacing the alkynes with phenylpropiolic acid under optimized conditions. The present catalytic system was found to be robust, magnetically recoverable and recyclable 5 times without significant loss in its activity, offering a low E-factor and high atom economy (AE).

CuO/Fe2O3 NPs were found to be robust, green and sustainable nanocatalysts for the synthesis of trisubstituted propargylamines by the reaction of propiolic acid, secondary amines and aldehydes via decarboxylative A3 coupling reaction under solvent free conditions. Further, we explored the wide applicability of the present methodology by replacing the more reactive aldehydes with less reactive ketones to afford the tetrasubstituted propargylamines via decarboxylative KA2 reaction. The present method showed several advantages such as usage of magnetically recoverable with six times recyclability of nanocatalyst, follows green chemistry principles including low E-factor and high atom economy for the A3 and KA2 reactions as well as high turnover numbers through easy catalyst recycling.

A novel copper supported on hydromagnesite (Cu/HM) nanomaterial was prepared by a simple impregnation method at room temperature and characterized by PXRD, SEM, TEM, EDAX, XPS, ICP-AES and FT-IR techniques. The EDAX and XPS results revealed the presence of 8.82 wt % of copper in (+2) oxidation state. Three-component coupling of ketone and amine with alkyne to afford tetrasubstituted propargylamine is known as KA2 coupling, whereas the three-component reaction of aldehydes and amine with alkyne to give propargylamine is considered as an A3-coupling reaction. The Cu/HM was found to be an efficient heterogeneous catalyst for KA2 coupling reaction under solvent free condition, and A3 coupling strategy to afford the pyrrolo[1,2-a]quinolines in DEG as a green solvent. The high catalytic activity of Cu/HM in the A3 coupling strategy to afford propargylamine intermediate is due to the synergistic effect of both Cu2+ and Mg2+ active sites. The versatility of Cu/HM catalyst was also studied for the decarboxylative ...

CuI/CSP nanocomposites were found to be efficient and recyclable nanocatalysts for one-pot synthesis of aminoindolizines via A3 coupling reaction in the presence of ethylene glycol (EG) as a recyclable solvent. In contrast, chalcones were isolated when the reaction was performed in the presence of secondary amines such as piperidine, 3-methylpiperidine, pyrrolidine, and piperazine under solvent free conditions. The CuI/CSP was recycled for five times without significant loss in its catalytic activity. The anomalous selectivity in the formation of aminoindolizines and chalcones was dependent on solvents and secondary amines used for the reaction. The present methodology is facile and follows green principles with higher atom economy (94%) and smaller E-factor (0.06).

The anisotropic controlled assembly of nanobuilding blocks into uncommon uniform rectangular thin sheet morphology of hydromagnesite (RS-HM) with a high surface area of 110 m2/g was achieved by a simple conventional heating under green reaction condition. The synthesized RS-HM was calcined at 450 °C in the presence of air and resulted in the formation of MgO with a surface area 120 m2/g. RS-HM was found to be a more efficient catalyst than MgO for the synthesis of novel 3-substituted indoles via Yonemitsu-type condensation selectively in excellent yields. The present method has advantages such as environmentally benign, ease to handle, selectivity and excellent yields, low E-factor (0.15) and high atom economy (96%).

Tetrabutylammonium glycinate [TBA][Gly] ionic liquid was found to be an efficient recyclable and biodegradable organocatalyst for selective synthesis of 3-substituted indoles and indolyl-4H-chromenes. The reaction between substituted aliphatic/aromatic aldehydes, malononitrile, and indoles in the presence of [TBA][Gly] IL at 60 °C under solvent free conditions afforded 3-substituted indoles in excellent yields. Indolyl-4H-chromenes were achieved in excellent yields by replacing the benzaldehydes with salicylaldehyde under optimized reaction conditions.

A nanocomposite consisting of reduced graphene oxide and zinc oxide nanoparticles (RGO/ZnO) with unique structural features was developed as an efficient, sustainable, amphiphilic, heterogeneous catalyst for the synthesis of various 3-substituted indoles in water. The catalyst was recycled six times without significant loss in catalytic activity. The higher environmental compatibility and sustainability factors such as smaller E-factor and higher atom economy make the present methodology a true green and sustainable process for the synthesis of various biologically important 3-substituted indoles.

Trichomoniasis is the most prevalent, curable sexually transmitted disease (STD), which increases risk of viral STDs and HIV. However, drug resistance has been developed by some strains of Trichomonas vaginalis against Metronidazole (MTZ), the FDA approved drug against trichomoniasis. In the present study twenty two chalcone hybrids of metronidazole have been synthesized in a quest to get new molecules with higher potential against metronidazole-resistant T. vaginalis. All new hybrid molecules were found active against T. vaginalis with varying levels of activity against MTZ-susceptible and resistant strains. Eight compounds (4a, 4c, 4d, 4e, 4f, 4h, 4q and 4s) were found as active as the standard drug with an MIC of 1.56 μg/ml against MTZ-susceptible strain. However, compounds 4e, 4h and 4m were 4-times more active than MTZ against drug-resistant T. vaginalis, amongst which 4e and 4h were most promising against both susceptible and resistant strains.

Tetrabutylammonium valinate ionic liquid [NBu4][Val] supported on 3-chloropropyltriethoxysilane grafted superparamagnetic Fe3O4 NPs (VSF) was synthesized and characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electronic microscopy (TEM), scanning electronic microscopy (SEM), thermal gravimetric analysis (TGA), and vibrating sample magnetometer (VSM). The VSF catalyst was used as an efficient “quasi-homogeneous” catalyst for the multi-component synthesis of 1,4-dihydropyridines and 2-amino-4-(indol-3-yl)-4H-chromenes at room temperature. The VSF catalyst was recovered using an external magnet and recycled six times without a significant loss in the catalytic activity. Moreover, VSF as a “quasi-homogeneous” catalyst can bridge the gap between homogeneous and heterogeneous catalyses.

A form of hydromagnesite (HM) with flower-like thin-sheet morphology was synthesized by an environmentally benign approach using simple conventional heating at moderate temperature without using any template in water as medium. The versatility of this HM catalyst was studied in the synthesis of flavanones, flavonols and the multicomponent synthesis of 1,4-dihydropyridines in water. The recyclability of catalyst was studied for six times and there was no appreciable loss in its catalytic activity.

Tetrabutylammonium glycinate [TBA][Gly] ionic liquid was found to be an efficient recyclable and biodegradable organocatalyst for selective synthesis of 3-substituted indoles and indolyl-4H-chromenes. The reaction between substituted aliphatic/aromatic aldehydes, malononitrile, and indoles in the presence of [TBA][Gly] IL at 60 °C under solvent free conditions afforded 3-substituted indoles in excellent yields. Indolyl-4H-chromenes were achieved in excellent yields by replacing the benzaldehydes with salicylaldehyde under optimized reaction conditions.

A facile protocol, using ethylene glycol as a recyclable promoting medium for the three component reaction of indoles, aldehydes, and amines to form 3-aminoalkylated indoles, is developed.

A form of hydromagnesite with flower-like thin-sheet morphology is prepared and successfully employed as the catalyst for the synthesis of flavones (II), flavonol (III) and the multicomponent synthesis of 1,4-dihydropyridines (VII).

The L-proline confined zeolite catalyst is effective in the preparation of the novel spirocyclic pyrimidine derivatives in the three-component condensation of lactams/cyclic ketones, amines, and formaldehyde.

A class of hybrid molecules consisting of 4-aminoquinoline and pyrimidine were synthesized and tested for antimalarial activity against both chloroquine (CQ)-sensitive (D6) and chloroquine (CQ)-resistant (W2) strains of Plasmodium falciparum through an in vitro assay. Eleven hybrids showed better antimalarial activity against both CQ-sensitive and CQ-resistant strains of P. falciparum in comparison to standard drug CQ. Four molecules were more potent (7–8-fold) than CQ in D6 strain, and eight molecules were found to be 5–25-fold more active against resistant strain (W2). Several compounds did not show any cytotoxicity up to a high concentration (60 μM), others exhibited mild toxicities, but the selective index for the antimalarial activity was very high for most of these hybrids. Two compounds selected for in vivo evaluation have shown excellent activity (po) in a mouse model of Plasmodium berghei without any apparent toxicity. The X-ray crystal structure of one of the compounds was also determined.

A novel ethylenediammonium diformate–polyethylene glycol (EDDF-PEG600) system was developed as a catalyst for the Knoevenagel condensation and Knoevenagel initiated three-component one-pot synthesis of 4H-pyrans at room temperature with high yields and in short reaction times. Further, the EDDF-PEG600 catalytic system was recycled six times without any appreciable loss in its activity and hence can be termed as a green, environmentally benign catalytic system. A plausible mechanism depicting the ambiphilic nature of EDDF (catalyst) and PEG (promoting medium) acting in synergy has been proposed.

A novel L-proline confined FAU zeolite catalyst system has been developed by confinement of L-proline in faujasite zeolite and its catalytic activity has been tested in the aqueous mediated synthesis of novel 1′,3′-di-(4-methylphenyl)-2′,3′,4′,6′-tetrahydro-1′H-spiro[indoline-3,5′-pyrimidin]-2-one (4a) and 1′,3′-di-(4-methylphenyl)-2′,3′,4′,6′-tetrahydro-1′H-spiro[indene-2,5′-pyrimidin]-1(3H)-one (4d) for the first time via the one-pot three-component condensation of lactams/cyclic ketones, amines and aqueous formaldehyde. The recyclability of the novel catalyst system was studied, which resulted in no loss of catalytic activity up to five cycles.