Tandem Protocol of Hexahydroquinoline Synthesis Using [H2-DABCO][HSO4]2 Ionic Liquid as a Green Catalyst at Room Temperature

Green, eco-benign, and sustainable synthesis is paramount in present chemistry. Here, a facile, efficient, and [H₂-DABCO][HSO₄]₂ ionic-liquid-catalyzed one-pot multicomponent synthesis of hexahydroquinolines was reported under ambient reaction conditions. The reaction of 1,3-dicarbonyls, malononitrile, and ammonium acetate with various aldehydes in the presence of an ionic liquid catalyst and EtOH solvent at room temperature afforded excellent yields (76-100%) of hexahydroquinolines under a short reaction time (5-15 min). Mild reaction conditions, broad substrate scope (28 derivatives), and column-chromatography-free synthesis with excellent catalytic efficiency and good recyclability rendered this protocol superior and practical. The greenness of the present method was assessed through eco-score and E-factor. The significant results in gram-scale synthetic conditions validate its applicability in industries as well as academia in the near future.

Solvent-free mechanochemical multicomponent preparation of 4H-pyrans catalyzed by Cu2(NH2-BDC)2(DABCO) metal-organic framework

4H-pyrans have been prepared through a mechanochemical multicomponent reaction (MCR) of different aldehydes, malononitrile, and various 1,3-dicarbonyl compounds, catalyzed by an amine-functionalized metal-organic framework (MOF) Cu₂(NH₂-BDC)₂(DABCO) as a heterogeneous catalyst with good to excellent yields.

Catalytic Esterification of Levulinic Acid into the Biofuel n-Butyl Levulinate over Nanosized TiO2 Particles

Levulinic esters, synthesized by the esterification of biomass-derived levulinic acid with various alcohols, is an important chemical that plays an essential role in the fields of biomass fuel additives, organic synthesis, and high value-added products. In the present work, the catalytic esterification of levulinic acid with n-butyl alcohol was selected as a typical model reaction to investigate the catalytic performance of an inexpensive commercial catalyst, titanium oxide nanoparticles. The influences of reaction time, reaction temperature, and catalyst loading on the conversion of levulinic acid to n-butyl levulinate were systematically examined through single-factor experiments. Additionally, the optimization of the reaction conditions was further investigated by a Box-Behnken design in response to the surface methodology. The desired product, n-butyl levulinate, with a good yield (77.6%) was achieved under the optimal conditions (reaction time of 8 h, reaction temperature of 120 °C, and catalyst dosage of 8.6 wt.%) when using titanium oxide nanoparticles as catalysts. Furthermore, it was found that addition of water to the catalytic system facilitated the reaction process, to some extent. This study reveals that the nanosized TiO₂ material_, as an efficient solid acid catalyst, had good catalytic performance and stability for the esterification of levulinic acid after six consecutive uses.

Anise Essential Oil as a Sustainable Substrate in the Multicomponent Double Povarov Reaction for Julolidine Synthesis

The use of star anise oil from a natural source as a dienophile in the multicomponent double Povarov reaction (MCPRs) to produce highly substituted julolidines with diverse technological applications is described. Within the framework of green chemistry, these MCPRs have many advantages such as (i) use of water in the reaction, (ii) creation of up to six bonds in one sequence, (iii) water as a sole waste, (iv) 100% of carbon economy, (v) a metal-free process, and (vi) nontoxic and reusable organocatalysts. These advantages, along with a simple workup procedure, make this protocol greener for the synthesis of julolidines.

In situ synthesis of SO3H supported Fe3O4@resorcinol-formaldehyde resin core/shell and its catalytic evaluation towards the synthesis of hexahydroquinoline derivatives in green conditions

A novel spherically shaped core@double-shell acidic nanocatalyst (Fe₃O₄@SiO₂@RF-SO₃H) [RF: resorcinol-formaldehyde resin] was prepared in situ and completely characterized using X-ray diffraction, Fourier transform infrared spectroscopy, vibrating sample magnetometry, energy dispersive X-ray spectroscopy, thermogravimetric analysis, transmission electron microscopy and field-emission scanning electron microscopy. The concentration of H⁺ loaded on the Fe₃O₄@SiO₂@RF was reported to be 1.3 mmol g^-1. The well-defined Fe₃O₄@SiO₂@RF-SO₃H core-shell heterostructures exhibited high stability, efficient recyclability (10 cycles), and promoted catalytic activity for one-pot condensation reaction between the aromatic aldehydes, dimedone, malononitrile, and ammonium acetate for the synthesis of hexahydroquinoline derivatives.

In-situ formation of durable akaganeite (β-FeOOH) nanorods on sulfonate-modified poly(ethylene terephthalate) fabric for dual-functional wastewater treatment

Industrial oily wastewater with dye-pollution is a critical environmental issue for water purification. However, the fabrication of effective and stable materials for oil-water separation and simultaneous degradation of organic contaminants remains a critical challenge. Herein, we report a new process for in-situ formation of akaganeite (β-FeOOH) nanorods layer on the surface of poly(ethylene terephthalate) (PET) fabric via radiation-induced graft polymerization of glycidyl methacrylate, which is then sulfonated and mineralized. The resultant product is labeled as β-FeOOH@PET, which exhibits dual purification by demonstrating an effective oil-water separation and organic dyes photodegradation under the illumination of visible light. It provides stable performance even after 1000 wash cycles. The sulfonated layer acts as not only an electronic transport layer to prevent electron-hole recombination, but also as an anchored interface for immobilizing β-FeOOH nanorods on the sulfonated layer via strong covalent bonds. Overall, the superhydrophilicity and underwater superoleophobicity of β-FeOOH@PET fabric, along with its robustness with a flexible organic substrate and its dual purification function, provide a new insight toward oily wastewater remediation and water purification in large-scale applications.

5-Oxo-hexahydroquinoline: an attractive scaffold with diverse biological activities

5-Oxo-hexahydroquinoline (5-oxo-HHQ) represents a biologically attractive fused heterocyclic core. Various synthetic analogs of 5-oxo-HHQ have been synthesized and assessed for different biological activities. Some derivatives have exhibited myorelaxant, analgesic, anticancer, antibacterial, antifungal, antitubercular, antimalarial, antioxidant, anti-inflammatory, multidrug resistance reversal, anti-Alzheimer, neuroprotective, antidiabetic, antidyslipidemic and antiosteoporotic activities. This review provides a comprehensive report regarding the preparation and pharmacological characterization of 5-oxo-HHQ derivatives that have been reported so far. This information will be beneficial for medicinal chemists in the field of drug discovery to design and develop new and potent therapeutical agents bearing the 5-oxo-HHQ nucleus.

A new type of SO3H-functionalized magnetic-titania as a robust magnetically-recoverable solid acid nanocatalyst for multi-component reactions

This paper highlights a novel synthetic strategy for the preparation of robust and magnetically-recoverable solid acid nanocatalysts.