Eco-friendly synthesis of chromeno[4,3-b]chromenes with a new photosensitized WO3/ZnO@NH2-EY nanocatalyst

Visible-Light Photocatalysis for Sustainable Chromene Synthesis and Functionalization

Chromenes represent a biologically significant family of heterocycles, widely present in pharmaceutical compounds and secondary metabolites. Their importance in synthesis and medicinal chemistry has driven continuous efforts to develop advanced and efficient synthetic methodologies. Over the past decade, photoredox catalysis has revolutionized Organic Synthesis, offering innovative and sustainable strategies for the construction and functionalization of complex molecules. The synthesis of chromene derivatives has greatly benefited from the integration of visible-light-promoted methodologies, which utilize light as an abundant and non-toxic energy source, enabling greener chemical transformations. In this review, the latest progress in visible-light-mediated approaches for the synthesis of chromene derivatives, along with the photochemical reactivity of these relevant frameworks, are summarized.

TiO2/CuWO4 heterojunction photocatalyst in the preparation of cardiovascular chromeno[4,3-b]chromene drugs

Chromeno[4,3-b]chromenes have shown potential as effective drugs against cardiovascular diseases. This study centered on a novel heterojunction nanocomposite TiO2/CuWO4, which incorporates titanium dioxide (TiO2) and copper tungstate(vi) to improve photocatalytic efficiency. The characterization of the TiO2/CuWO4 photocatalyst was performed using various techniques, including FT-IR, XRD, TEM, DRS, SEM, EDS, and XPS. TiO2/CuWO4 demonstrated significant effectiveness as a photocatalyst for the synthesis of chromeno[4,3-b]chromene derivatives, which show potential antibacterial and antifungal properties beneficial for oral health concerns such as dental caries and periodontal disease. While TiO2 can absorb light to produce electrons and holes under direct illumination, its photocatalytic efficiency is improved when paired with CuWO4. The research also explored the influence of several factors, including the quantity of photocatalyst, reaction duration, temperature, solvent selection, and the reusability of the nanocomposite. Optimal reaction conditions were found to involve 1 mmol of dimedone, benzaldehyde, and 4-hydroxycoumarin, using 12 mg of TiO2/CuWO4 in 4 mL of ethanol, subjected to irradiation from a green laser at room temperature for 30 minutes. The results indicate that the TiO2/CuWO4 heterojunction ranks among the most effective options for photocatalytic synthesis of chromeno[4,3-b]chromene derivatives.

L-Proline-catalysed synthesis of chromeno[2,3-b]chromene from 4-hydroxy-2H-chromene-2-thione and an anti-proliferative study

The reactivity of 4-hydroxy-2H-chromene-2-thione is investigated with aryl aldehydes and 5,5-dimethylcylohexane-1,3-dione (dimedone) in the presence of 20 mol% L-proline in toluene at 90 °C. Instead of the expected linear product with a sulphur atom in the ring provided by 4-hydroxydithiocoumarin or an angular product obtained from 4-hydroxycoumarin, the hitherto unreported products, 12-aryl substituted chromeno[2,3-b]chromenes (4), were obtained in good to excellent yields. The reaction proceeds through a three-component reaction via Knoevenagel condensation between dimedone with an aromatic aldehyde followed by Michael addition with 4-hydroxy-2H-chromene-2-thione. In addition, a molecular docking study of all the derivatives was performed and among them, four compounds exhibited anti-proliferative activity and elevated ROS generation in breast cancer (MCF7) cell lines.

ZnO-ZnS Heterostructure as a Potent Photocatalyst in the Preparation of Some Substituted Chromenes and Remarkable Antigastrointestinal Cancer Activity

The nanosized hybrid material ZnO-ZnS was synthesized using the well-known sol-gel method, as a simple and environmentally friendly procedure. The material was then characterized using various techniques including FESEM, TEM, UV-vis, DRS, EDS, XRD, and FT-IR. The characterization studies revealed the generation of ZnO-ZnS nanoparticles with a mean size of around 25 nm. Moreover, DRS analysis provided a band gap of 3.05 eV for this nanomaterial. The photocatalytic properties of the ZnO-ZnS heterojunction was investigated in the synthesis of some substituted chromenes under mild reaction conditions. The results showed that the prepared nanophotocatalyst exhibits significantly higher activity compared to its individual components (ZnO and ZnS) and provides 73-87% yield with 0.01 g of ZnO-ZnS after 30 min. In addition, the nanophotocatalyst demonstrated a high reusability in the desired condensation reaction. The enhanced photocatalytic activity of ZnO-ZnS can be attributed to the slower recombination of the electron-hole pairs in this semiconductor material. The reactive species OH•, •O2-, and h+ are believed to play important roles in the photocatalytic system. Furthermore, cellular toxicity of ZnO-ZnS nanoparticles was evaluated on HCT-116 human gastrointestinal cancer cell line by MTT assay. The results proved a distinct reduction of cell viability, proofing cytotoxicity of nanoparticles on the cancer cells. This study highlights the potential of the nanoparticles against gastrointestinal cancer.

Highly efficient and recyclable novel spindles Fe2O3@SiO2/In2O3 nanomagnetic catalyst designed for green synthesis of azomethine compounds

A novel and reusable nanomagnetic catalyst, Fe2O3@SiO2/In2O3, was synthesized by a facile chemical approach in three successive steps. The nanocatalyst was characterized by FT-IR, XRD, SEM, EDX, TEM, and VSM. The XRD pattern displays the characteristic peaks of Fe2O3 and SiO2, accompanied by new peaks assigned to different planes of In2O3 that confirm the formation of In2O3 on the surface of Fe2O3@SiO2 core/shell spindles. The TEM micrographs show spindle-like particles of Fe2O3 covered with SiO2 shell, and the In2O3 nanoparticles in an average diameter of 20 nm are hung on the surface of the Fe2O3@SiO2. The nanomagnetic catalyst Fe2O3@SiO2/In2O3 was used for the transformation of the (4-nitrophenyl)-1-phenyl-1H-pyrazole-5-amine, and chalcones derivatives, into valuable azomethine compounds of 3-(substituted)-1-(pyridine-2-yl)allylidene)-3-(4-nitrophenyl)-1-phenyl-1H-pyrazole-5-amine with high rate and efficient catalyst recovery. The yield obtained through the catalytic route reached 90–95% in shorter reaction times compared with uncatalyzed reaction method.

Graphical abstract

Magnetic nanoparticle-supported eosin Y salt [SB-DABCO@eosin] as an efficient heterogeneous photocatalyst for the multi-component synthesis of chromeno[4,3-b]chromene in the presence of visible light

Heterogeneous photocatalysts present a favourable procedure to realize green and eco-friendly organic reactions. We have demonstrated an SB-DABCO@eosin catalyst in a green one-pot multi-component protocol for the production of various chromeno[4,3-b]chromenes via condensation of aromatic aldehydes and dimedone under the photo-redox catalyst bearing eosin Y using visible light. The synthesized nanocatalyst was characterized using various physicochemical techniques such as FT-IR, XRD, EDX, UV-vis, SEM, TGA and DRS. The significant advantages of the present methodology include excellent yield, cost-effectiveness, easy work-up, 100% atom economy, broad substrate scope, easy separation and efficient recycling. Furthermore, the evidence showed that the investigated condensation reaction proceeds via a radical mechanism, which proved the need for reactive species such as OH˙ and ˙O2 - in the photocatalytic process. In addition to the improved handling and process control, the yield of products and the rate of reactions have increased considerably in the present strategy. Reproducibility studies also guarantee good reusability and stability of the nanocatalyst for at least five runs.

Catalytic Approaches to Multicomponent Reactions: A Critical Review and Perspectives on the Roles of Catalysis

In this review, we comprehensively describe catalyzed multicomponent reactions (MCRs) and the multiple roles of catalysis combined with key parameters to perform these transformations. Besides improving yields and shortening reaction times, catalysis is vital to achieving greener protocols and to furthering the MCR field of research. Considering that MCRs typically have two or more possible reaction pathways to explain the transformation, catalysis is essential for selecting a reaction route and avoiding byproduct formation. Key parameters, such as temperature, catalyst amounts and reagent quantities, were analyzed. Solvent effects, which are likely the most neglected topic in MCRs, as well as their combined roles with catalysis, are critically discussed. Stereocontrolled MCRs, rarely observed without the presence of a catalytic system, are also presented and discussed in this review. Perspectives on the use of catalytic systems for improved and greener MCRs are finally presented.