Heterocyclic reaction inducted by Brønsted–Lewis dual acidic Hf-MOF under microwave irradiation

Advances in the synthetic strategies of benzoxazoles using 2-aminophenol as a precursor: an up-to-date review

Benzoxazole is a resourceful and important member of the heteroarenes that connects synthetic organic chemistry to medicinal, pharmaceutical, and industrial areas. It is a bicyclic planar molecule and is the most favorable moiety for researchers because it has been extensively used as a starting material for different mechanistic approaches in drug discovery. The motif exhibits a high possibility of broad substrate scope and functionalization to offer several biological activities like anti-microbial, anti-fungal, anti-cancer, anti-oxidant, anti-inflammatory effects, and so on. There has been a large upsurge in the synthesis of benzoxazole via different pathways. The present article presents recent advances in synthetic strategies for benzoxazole derivatives since 2018. A variety of well-organized synthetic methodologies for benzoxazole using 2-aminophenol with aldehydes, ketones, acids, alcohols, isothiocyanates, ortho-esters, and alkynones under different reaction conditions and catalysts, viz. nanocatalysts, metal catalysts, and ionic liquid catalysts, with other miscellaneous techniques has been summarized.

Chitosan bead containing metal-organic framework encapsulated heteropolyacid as an efficient catalyst for cascade condensation reaction

Using cyclodextrin and chitosan that are bio-based compounds, a novel bi-functional catalytic composite is designed, in which metal-organic framework encapsulated phosphomolybdic acid was incorporated in a dual chitosan-cyclodextrin nanosponge bead. The composite was characterized via XRD, TGA, ICP, BET, NH₃-TPD, FTIR, FE-SEM/EDS, elemental mapping analysis and its catalytic activity was examined in alcohol oxidation and cascade alcohol oxidation-Knoevenagel condensation reaction. It was found that the designed catalyst that possess both acidic feature and redox potential could promote both reactions in aqueous media at 55 °C and various substrates with different electronic features could tolerate the aforementioned reactions to furnish the products in 75-95% yield. Furthermore, the catalyst could be readily recovered and recycled for five runs with slight loss of the catalytic activity. Notably, in this composite the synergism between the components led to high catalytic activity, which was superior to each component. In fact, the amino groups on the chitosan served as catalysts, while cyclodextrin nanosponge mainly acted as a phase transfer agent. Moreover, measurement of phosphomolybdic acid leaching showed that its incorporation in metal-organic framework and bead structure could suppress its leaching, which is considered a drawback for this compound. Other merits of this bi-functional catalyst were its simplicity, use of bio-based compounds and true catalysis, which was proved via hot filtration.

An efficient approach for the green synthesis of biologically active 2,3-dihydroquinazolin-4(1H)-ones using a magnetic EDTA coated copper based nanocomposite

2,3-Dihydroquinazolinone derivatives are known for antiviral, antimicrobial, analgesic, anti-inflammatory, and anticancer activities. However, recent approaches used for their synthesis suffer from various drawbacks. Therefore, we have fabricated a highly efficient magnetic EDTA-coated catalyst, Fe₃O₄@EDTA/CuI via a simple approach. The ethylenediamine tetraacetic acid (EDTA) plays a crucial role by strongly trapping the catalytic sites of CuI nanoparticles on the surface of the Fe₃O₄ core. The designed nanocatalyst demonstrates its potential for the catalytic synthesis of 2,3-dihydroquinazolinones using 2-aminobenzamide with aldehydes as the reaction partners. The nanocatalyst was thoroughly characterized through X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), vibrating sample magnetometry (VSM), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma analysis (ICP). The physiochemically characterized nanocatalyst was tested for synthesis of 2,3-dihydroquinazolinones and higher yields of derivatives were obtained with less time duration. Moreover, the catalytic synthesis is easy to operate without the use of any kind of additives/bases. Furthermore, the catalyst was magnetically recoverable after the completion of the reaction and displayed reusability for six successive rounds without any loss in its catalytic efficiency (confirmed by XRD, SEM, and TEM of the recycled material) along with very low leaching of copper (2.12 ppm) and iron (0.06 ppm) ions. Also, the green metrics were found in correlation with the ideal values (such as E factor (0.10), process mass intensity (1.10), carbon efficiency (96%) and reaction mass efficiency (90.62%)).

The chemistry and applications of hafnium and cerium(iv) metal-organic frameworks

The coordination connection of organic linkers to the metal clusters leads to the formation of metal-organic frameworks (MOFs), where the metal clusters and ligands are spatially entangled in a periodic manner. The immense availability of tuneable ligands of different length and functionalities gives rise to robust molecular porosity ranging from several angstroms to nanometres. Among the large family of MOFs, hafnium (Hf) based MOFs have been demonstrated to be highly promising for practical applications due to their unique and outstanding characteristics such as chemical, thermal, and mechanical stability, and acidic nature. Since the report of UiO-66(Hf) and DUT-51(Hf) in 2012, less than 200 Hf-MOFs (ca. 50 types of structures) have been reported. Besides, tetravalent cerium [Ce(iv)] has been proven to be capable of forming similar topological MOF structures to Zr and Hf since its first discovery in 2015. So far, ca. 40 Ce(iv) MOFs with 60% having UiO-66-type structure have been reported. This review will offer a holistic summary of the chemistry, uniqueness, synthesis, and applications of Hf/Ce(iv)-MOFs with a focus on presenting the development in the Hf/Ce(iv)-clusters, topologies, ligand structures, synthetic strategies, and practical applications of Hf/Ce(iv)-MOFs. In the end, we will present the research outlook for the development of Hf/Ce(iv)-MOFs in the future, including fundamental design of Hf/Ce(iv)-clusters, defect engineering, and various applications including membrane development, diversified types of catalytic reactions, irradiation absorption in nuclear waste treatment, water production and wastewater treatment, etc. We will also present the emerging computational approaches coupled with machine-learning algorithms that can be applied in screening Hf and Ce(iv) based MOF structures and identifying the best-performing MOFs for tailor-made applications in future practice.