Monomeric, Oligomeric, Polymeric, and Supramolecular Cyclodextrins as Catalysts for Green Chemistry

This review comprehensively covers recent developments of cyclodextrin-mediated chemical transformations for green chemistry. These cyclic oligomers of glucose are nontoxic, eco-friendly, and recyclable to accomplish eminent functions in water. Their most important feature is to form inclusion complexes with reactants, intermediates, and/or catalysts. As a result, their cavities serve as sterically restricted and apolar reaction fields to promote the efficiency and selectivity of reactions. Furthermore, unstable reagents and intermediates are protected from undesired side reactions. The scope of their applications has been further widened through covalent or noncovalent modifications. Combinations of them with metal catalysis are especially successful. In terms of these effects, various chemical reactions are achieved with high selectivity and yield so that valuable chemicals are synthesized from multiple components in one-pot reactions. Furthermore, cyclodextrin units are orderly assembled in oligomers and polymers to show their cooperation for advanced properties. Recently, cyclodextrin-based metal-organic frameworks and polyoxometalate-cyclodextrin frameworks have been fabricated and employed for unique applications. Cyclodextrins fulfill many requirements for green chemistry and should make enormous contributions to this growing field.

γ-Cyclodextrins as Supramolecular Reactors for the Three-component Aza-Darzens Reaction in Water

In recent decades, many efforts have been devoted to studying reactions catalyzed in nanoconfined spaces. The most impressive aspect of catalysis in nanoconfined spaces is that the reactivity of the molecules can be smartly driven to disobey classical behavior. A green and efficient three-component aza-Darzens (TCAD) reaction using a catalytic amount of γ-cyclodextrins (CDs) in water has been developed to synthesize N-phenylaziridines. CDs effectively performed this reaction in an environmentally friendly setting, achieving good yields. The same reaction was then performed using polymeric γ-CD such as a γ-cyclodextrin polymer crosslinked (GCDPC) with epichlorohydrin, a sponge-like macroporous γ-cyclodextrin-based cryogel (GCDC), and a γ-cyclodextrin-based hydrogel (GCDH). The homogeneous and heterogeneous catalyst recovery was then studied, and it was proved to be easily recycled several times without relevant activity loss. Water, as a unique and eco-friendly reaction medium, has been utilized for the first time, to the best of our knowledge, in this reaction. The inclusion of the reagents in CDs has been studied and rationalized by NMR spectroscopy experiments and molecular modeling calculations. The credit of the presented protocol includes good yields and catalyst reusability and precludes the use of organic solvents.

Enhanced catalysis through structurally modified hybrid 2-D boron nitride nanosheets comprising of complexed 2-hydroxy-4-methoxybenzophenone motif

Tuning the structural architecture of the pristine two dimensional hexagonal boron nitride (h-BN) nanosheets through rational surface engineering have proven advantageous in the fabrication of competent catalytic materials. Inspired by the performance of h-BN based nanomaterials in expediting key organic transformations, we channelized our research efforts towards engineering the inherent surface properties of the exclusively stacked h-BN nanosheets through the incorporation of a novel competent copper complex of a bidentate chelating ligand 2-hydroxy-4-methoxybenzophenone (BP). Delightfully, this hybrid nanomaterial worked exceptionally well in boosting the [3 + 2] cycloaddition reaction of azide and nitriles, providing a facile access to a diverse variety of highly bioactive tetrazole motifs. A deep insight into the morphology of the covalently crafted h-BN signified the structural integrity of the exfoliated h-BN@OH nanosheets that exhibited lamellar like structures possessing smooth edges and flat surface. This interesting morphology could also be envisioned to augment the catalysis by allowing the desired surface area for the reactants and thus tailoring their activity. The work paves the way towards rational design of h-BN based nanomaterials and adjusting their catalytic potential by the use of suitable complexes for promoting sustainable catalysis, especially in view of the fact that till date only a very few h-BN nanosheets based catalysts have been devised.

Nanomaterial catalyzed green synthesis of tetrazoles and its derivatives: a review on recent advancements

Tetrazoles are indispensable nitrogen containing heterocyclic scaffolds that offer a broad spectrum of applications in various domains such as medicinal chemistry, high energy material science, biochemistry, pharmacology etc. Owing to their useful applications, a wide range of catalysts have been explored for green synthesis of tetrazole derivatives. In recent times, nanomaterials have been emerged as extremely efficient catalysts for different organic transformations because of their high surface area-to-volume ratio, easy surface modification, simple fabrications, easy recovery and reusability. In this article, we have presented an overview of utilization of various nano-catalysts, nanocomposites and other solid-supported nanomaterials as an efficient environmental benign catalytic system for green synthesis of tetrazoles and derivatives. This review will provide an exclusive emphasis on boehmite, magnetic, copper, carbon, MCM-41, and composite based nanomaterials that have been developed since the year 2010 for the synthesis of tetrazole derivatives. In addition, we have briefly discussed the fabrication, functionalization and characterization of some novel nanomaterials and their advantages in the synthesis of tetrazole and its derivatives along with the reaction mechanism that involves synthesis of tetrazole derivatives via nanomaterials catalysed reactions.

The anchoring of a Cu(ii)-salophen complex on magnetic mesoporous cellulose nanofibers: green synthesis and an investigation of its catalytic role in tetrazole reactions through a facile one-pot route

Today, most synthetic methods are aimed at carrying out reactions under more efficient conditions and the realization of the twelve principles of green chemistry. Due to the importance and widespread applications of tetrazoles in various industries, especially in the field of pharmaceutical chemistry, and the expansion of the use of nanocatalysts in the preparation of valuable chemical reaction products, we decided to use an (Fe3O4@NFC@NSalophCu)CO2H nanocatalyst in this project. In this study, the synthesis of the nanocatalyst (Fe3O4@NFC@NSalophCu)CO2H was explained in a step-by-step manner. Confirmation of the structure was obtained based on FT-IR, EDX, FE-SEM, TEM, XRD, VSM, DLS, TGA, H-NMR, and CHNO analyses. The catalyst was applied to the synthesis of 5-substituted-1H-tetrazole and 1-substituted-1H-tetrazole derivatives through multi-component reactions (MCRs), and the performance was assessed. With advances in science and technology and increasing environmental pollution, the use of reagents and methods that are less dangerous for the environment has received much attention. Therefore, following green chemistry principles, with the help of the (Fe3O4@NFC@NSalophCu)CO2H salen complex as a nanocatalyst that is recyclable, cheap, safe, and available, the use of water as a green solvent, and reduced reaction times, the synthesis of tetrazoles can be achieved.

A new efficient domino approach for the synthesis of coumarin-pyrazolines as antimicrobial agents targeting bacteriald-alanine-d-alanine ligase

The inhibition ofd-alanine-d-alanine ligase (Ddl) prevents bacterial growth, which makes this enzyme an attractive and viable target in the urgent search for novel effective antimicrobial drugs.

An intramolecular relay catalysis strategy for Knoevenagel condensation and 1,3-dipolar cycloaddition domino reactions

A relay catalysis strategy was established by using a bifunctional catalyst which was prepared by immobilization of organic chains containing secondary amine and Cu(ii) complex onto silica-coated nano-Fe₃O₄. The simply prepared nanoparticles acted as efficient, intramolecular relays and magnetically recyclable base-metal bifunctional catalysts for Knoevenagel condensation and 1,3-dipolar cycloaddition domino reactions to prepare 5-substituted 1H-tetrazoles with excellent yields.

A magnetically recoverable bifunctional catalyst was synthesized and effectively used in Knoevenagel condensation and 1,3-dipolar cycloaddition domino reactions.

Unprecedented Concomitant Formation of Cu2O-CD Nano-Superstructures During the Aerobic Oxidation of Alcohols and Their Catalytic Use in the Propargylamination Reaction: A Simultaneous Catalysis and Metal Waste Valorization (SCMWV) Method

Copper-cyclodextrins (CDs)-catalyzed aerobic oxidation of alcohols under aqueous conditions and a concomitant formation of Cu₂O-cyclodextrin nano-superstructures (Cu₂O-CD nps) during the reaction are reported. The use of affordable copper and cyclodextrin combination for aerobic oxidation precluding organic solvents makes it a benign methodology. Intriguingly, a diverse array of Cu₂O-CD nps with unique morphologies was obtained by varying copper salts, cyclodextrins, and bases. The nano-superstructures were characterized by different techniques, such as X-ray diffraction, X-ray photoelectron spectroscopy, differential scanning calorimetry-thermogravimetric analysis, scanning electron microscopy, time of flight secondary-ion mass spectrometry, and transmission electron microscopy to confer their authenticity. Interestingly, the nano-superstructures showed promising catalytic efficiency for a one-pot three-component propargylamination reaction. The used particles were found to be recoverable and recyclable for propargylamination for up to three cycles, with no loss of catalytic activity. Moreover, the concomitant formation of Cu₂O-CD nanostructures and their self-segregation during an aerobic oxidation reaction under homogenous conditions is a first-of-its-kind method depicting simultaneous catalysis and metal waste valorization (SCMWV). Overall, this new approach of reaping the benefits of homogenous metal catalysis and simultaneously sequestrating the metal into a high-value product might pave the way to develop many such SCMWV protocols in future.

γ-Cyclodextrin as a Catalyst for the Synthesis of 2-Methyl-3,5-diarylisoxazolidines in Water

A green and efficient 1,3-dipolar cycloaddition of nitrones with different styrenes and cinnamates using a catalytic amount of γ-cyclodextrin (γ-CD) in water has been developed to give substituted isoxazolidines. γ-CD was found to be highly efficacious in carrying out this reaction under an eco-friendly environment, affording moderate to excellent yields and, in some cases, excellent diastereomeric excess (up to >95%) at 100 °C in 8-12 h. The catalyst can be easily recuperated and recycled for several times without loss of activity. Water, an eco-friendly reaction medium, has been utilized for the first time, to the best of our knowledge, in this reaction. The credit of the presented protocol includes high yields and catalyst reusability, and precludes the use of organic solvents. The use of in silico calculations allowed us to rationalize the obtained results and to improve the stereoselectivity.

Synthesis of D–D–A-type small organic molecules with an enlarged linker system towards organic solar cells and the effect of co-adsorbents on cell performance

The synthesis of two D–D–A type novel small molecules and their applications in organic solar cells have been studied.

Magnetically separable Fe3O4@chitin as an eco-friendly nanocatalyst with high efficiency for green synthesis of 5-substituted-1H-tetrazoles under solvent-free conditions

Eco-friendly Fe₃O₄@chitin nanocatalyst was prepared, characterized and applied for synthesis of 5-substituted-1H-tetrazoles in a green media.

The first report on the eco-friendly synthesis of 5-substituted 1H-tetrazoles in PEG catalyzed by Cu(ii) immobilized on Fe3O4@SiO2@l-arginine as a novel, recyclable and non-corrosive catalyst

Cu(ii) immobilized on Fe₃O₄@SiO₂@l-arginine as a novel nanostructured compound catalyzed the cycloaddition reaction of organic nitriles and sodium azide to produce 5-substituted 1H-tetrazoles.

Ecofriendly synthesis of a heterogeneous polyvinyl alcohol immobilized copper(ii) Schiff base complex as an efficient, reusable catalyst for the one-pot three-component green preparation of 5-substituted 1H-tetrazoles under mild conditions

A new polymeric Cu(ii) Schiff base complex catalyst is developed, which shows high catalytic activity in the preparation of 5-substituted 1H-tetrazoles under mild and green conditions.

Facile synthesis of D–π–A structured dyes and their applications towards the cost effective fabrication of solar cells as well as sensing of hazardous Hg(ii)

Synthesis of two D–π–A dyes with a multidisciplinary application approach explained on the basis of electron sharing effects.

Bovine serum albumin catalyzed one-pot, three-component synthesis of dihydropyrano[2,3-c]pyrazole derivatives in aqueous ethanol

A BSA catalyzed synthesis of dihydropyrano[2,3-c]pyrazole derivatives via a one pot, three component reaction of an aldehyde/ketone/isatin, malononitrile and 3-methyl-1H-pyrazol-5-(4H)-one in H₂O–EtOH (7 : 3) at ambient temperature is reported.

OSU-6: A Highly Efficient, Metal-Free, Heterogeneous Catalyst for the Click Synthesis of 5-Benzyl and 5-Aryl-1H-tetrazoles

OSU-6, an MCM-41 type hexagonal mesoporous silica with mild Brönsted acid properties, has been used as an efficient, metal-free, heterogeneous catalyst for the click synthesis of 5-benzyl and 5-aryl-1H-tetrazoles from nitriles in DMF at 90 °C. This catalyst offers advantages including ease of operation, milder conditions, high yields, and reusability. Studies are presented that demonstrate the robust nature of the catalyst under the optimized reaction conditions. OSU-6 promotes the 1,3-dipolar addition of azides to nitriles without significant degradation or clogging of the nanoporous structure. The catalyst can be reused up to five times without a significant reduction in yield, and it does not require treatment with acid between reactions.

An efficient synthesis of 3-indolyl-3-hydroxy oxindoles and 3,3-di(indolyl)indolin-2-ones catalyzed by sulfonated β-CD as a supramolecular catalyst in water

Sulfonated-β-cyclodextrin (β-CD-SO3H) promoted efficient and fast electrophilic substitution reaction of indoles with various isatins reflux in water is reported affording various 3-indolyl-3-hydroxy oxindoles and 3,3-di(indolyl)indolin-2-ones in good to excellent yields in short reaction time.

A rapid metal free synthesis of 5-substituted-1H-tetrazoles using cuttlebone as a natural high effective and low cost heterogeneous catalyst

A convenient, rapid and metal free synthesis of 5-substituted-1H-tetrazoles by [3 + 2] cycloaddition reaction of nitriles with sodium azide. Cuttlebone as a natural low cost heterogeneous catalyst affords 5-substituted-1H-tetrazoles rapidly with high efficiency.

Cu(ii) immobilized on aminated epichlorohydrin activated silica (CAES): as a new, green and efficient nanocatalyst for preparation of 5-substituted-1H-tetrazoles

Reusable nanocatalyst was prepared and characterized an efficient and environmentally benign method of 5-substituted-1H-tetrazole synthesis was introduced.

ZrO2-β-cyclodextrin catalyzed synthesis of 2,4,5-trisubstituted imidazoles and 1,2-disubstituted benzimidazoles under solvent free conditions and evaluation of their antibacterial study

A series of 2,4,5-trisubstituted imidazoles and 1,2-disubstituted benzimidazoles catalyzed by ZrO₂-supported-β-cyclodextrin (ZrO₂-β-CD) under solvent free conditions have been synthesized and characterized by spectral methods.

Highly selective fluorimetric sensor for Cu2+and Hg2+using a benzothiazole-based receptor in semi-aqueous media and molecular docking studies

A new chemosensor (Z)-ethyl 2-((Z)-2-(benzo[d]thiazol-2-ylimino)-4-oxo-3-phenylthiazolidin-5-ylidene)acetate (receptor1) was designed and synthesized under catalyst-free conditions.