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Rationally designing distinct acidic and basic sites can greatly enhance performance and deepen our understanding of reaction mechanisms. In our current investigation, we studied the utilization of Brønsted acid sites within layered graphitic carbon nitride (g-C3N4) for the first time to enhance the rate of the Friedländer synthesis. The structural and surface analyses confirm the effective integration of -COOH and -SO3H groups into the g-C3N4 lattice. The surface-functionalized g-C3N4-CO-(CH2)3-SO3H exhibits a remarkable acceleration in quinoline formation, surpassing previously mentioned catalysts, and demonstrating notable recyclability under optimized mild reaction conditions. The heightened reaction rate observed over g-C3N4-CO-(CH2)3-SO3H is attributed to its elevated surface acidity. By probing the Friedländer reaction mechanism through surface characterization, examination of reaction intermediates, and investigation of substrate scope, we elucidate the pivotal role of Brønsted acid sites. This study constitutes a comprehensive exploration of metal-free heterogeneous catalysts for the Friedländer reaction, offering a unique contribution to the field. [ABSTRACT FROM AUTHOR]

We have successfully synthesized quinoline derivatives that exhibit easy scalability and responsiveness to multiple stimuli. These derivatives are capable of forming self-assembled nanoscopic aggregates in an aqueous medium. Consequently, when placed in an aqueous environment, we observe dual fluorescence originating from both twisted intramolecular charge transfer and aggregation-induced emission. The introduction of nerve gas agents, such as diethyl chlorophosphate (DClP) or diethylcyanophosphate (DCNP), to the probe molecules facilitates the charge-transfer process, resulting in a red-shift in absorption maxima. Notably, when operating in fluorescence mode, both of these analytes produce distinct output signals, making them easily distinguishable. DCNP generates a blue fluorescence, while the addition of DClP yields cyan fluorescence. Our mechanistic investigation reveals that the initial step involves phosphorylation of the quinoline nitrogen end. However, in the case of DCNP, the released cyanide ion subsequently attacks the carbonyl carbon centre, forming a cyanohydrin derivative. The response to these target analytes appears to be influenced by the nucleophilicity of the quinoline nitrogen end and the electrophilic nature of the carbonyl unit. [ABSTRACT FROM AUTHOR]

Recent research underscores the significance of metal-organic frameworks as catalysts, owing to their structural adaptability, substantial surface areas, adjustable pore dimensions, and customizable catalytic sites. Using Friedländer synthesis, we evaluated the catalytic potential of three synthesized metal-organic framework materials, MIL-53(Al), MIL-101(Cr), and MOF-5(Zn), in quinoline derivative synthesis. MIL-53(Al) outperformed MIL-101(Cr) and MOF-5(Zn), highlighting the vital role of Lewis acidic sites (Al3+) in quinoline production. Potentiometric titration analyses revealed MIL-53(Al)'s superior Lewis acid strength. Reaction optimization involved varying temperatures, catalyst loading, reaction duration, and solvents. MIL-53(Al) exhibited four-cycle recyclability. Mechanistic insights underscored Lewis acid strength and the significance of sites. The Al-based catalyst proficiently facilitated Friedlander synthesis, yielding enhanced conversion and considerable physiologically active quinoline yields. The findings offer insights into diverse catalytic strategies and demonstrate the adaptability of metal-organic framework materials in varied chemical reactions. The Al-based Lewis acid MOF catalyst MIL-53(Al) efficiently facilitated the Friedlander synthesis, resulting in improved conversion and significant yields of physiologically active quinolines. These findings provide insights into versatile catalytic strategies and showcase the adaptability of MOFs in diverse chemical reactions. [ABSTRACT FROM AUTHOR]

We report on the use of heterogeneous metal organic framework (MOF) catalysts for the Friedländer synthesis of 2‐aminoaryl ketone with α‐methylene carbonyl derivatives, a versatile and widely used method for the synthesis of quinoline derivatives. The importance of the Lewis and Brønsted acid sites and their spatial proximity have been explored. Postsynthetic modifications were made to introduce the Brønsted −SO3H acid sites in the pristine MIL‐53(Al). Two modifications were carried out, resulting in two different MOFs: MIL‐53(Al)−NH−(CH2)3−SO3H, in which there is a significant spatial distance between the Lewis and Brønsted sites, and MIL‐53(Al)−SO3H, where the two sites are in close proximity. The availability of sulfonic acid groups has a significant impact on their catalytic performance. The sulfonated MIL‐53(Al) material exhibited a high yield of quinoline derivatives under solventless and mild reaction conditions, with a wide substrate scope and good reusability. Mechanistic studies revealed that the dual acidic sites of the catalysts play an important role in the reaction mechanism. [ABSTRACT FROM AUTHOR]

[Display omitted] Multi component reactions over heterogeneous solid acid catalysts are extremely important owing to easy separation, amenable recycling, and prospective scaling up of the process. Here, we are reporting the synthesis of biologically important dihydropyrimidinones over postsynthetic modified Cr-based metal–organic framework materials as heterogeneous catalysts containing the bifunctional Lewis and Brønsted acid sites. Cr-based metal–organic frameworks contained coordinatively unsaturated metal sites as inherent Lewis acid sites, whereas postsynthetic modifications introduced the Brønsted acid sites in the framework. A direct one pot synthesis route was employed to produce the pristine MOF in pure aqueous medium without using any additives. The bulk structure, morphology, surface and bonding properties of the synthesized materials were thoroughly characterized with powder XRD, FTIR, XPS, FE-SEM, TGA, and N 2 sorption isotherms. A qualitative evolution of acid strength was carried out over the functionalized MOFs. Among the post synthetic functionalized materials, carboxylic acid functionalized framework exhibited a very high yield of dihydropyrimidinones under solvent less moderate reaction conditions. The catalyst also demonstrated a robust recyclability and wide substrate scope. Comparative study showed a very high catalytic activity of the postsynthetic modified MOFs in comparison to the reported literature. The reaction condition was optimized by varying parameters like solvent, temperature, reaction duration and catalyst loadings. The mechanistic studies indicated the involvement of both the Lewis and Brønsted sites acid sites of the catalysts in the multicomponent reaction. [ABSTRACT FROM AUTHOR]

In spite of having significant pharmacological importance, scalable synthesis of 2,2,4-trimethyl-1,2-H-dihydroquinoline (TMQ) is always being cumbersome due to harmful solvents, drastic reaction conditions, and high recovery cost of homogeneous catalysts. Heterogeneous catalytic condensation of aniline with acetone was employed here to synthesize TMQ. As efficient materials, Zn2+-, Sn2+-, and Cu2+-exchanged tungstophosphoric acid (TPA) supported on γ-Al2O3 was synthesized by microwave-assisted hydrothermal method. The synthesized catalysts were thoroughly characterized by XRD, Raman, FE-SEM, etc. and were screened for condensation reaction. Among the metal-exchanged catalysts, Zn0.5TPA/Al2O3 showed highest aniline conversion with the highest yield of TMQ up to three consecutive cycles. The acidic sites over the catalysts were probed by pyridine-adsorbed FT-IR spectra and NH3-TPD studies. The reaction conditions were optimized, and plausible reaction mechanistic pathway was derived from FT-IR and GC–MS data. [ABSTRACT FROM AUTHOR]