Synthesis and electroluminescent property of poly(p-phenylenevinylene)s bearing triarylamine pendants

Ag@TiO2 Nanocomposite as an Efficient Catalyst for Knoevenagel Condensation

In the present study, a new series of different heterocycles was synthesized through base-free Knoevenagel condensation of various aldehydes and active methylene-containing compounds using the hydrothermal developed Ag@TiO₂ as a heterogeneous catalyst. The catalyst was synthesized by mixing TiO₂ (P25) with AgNO₃ and hydrothermally treated in ethanol at 180 °C for 12 h. The developed Ag@TiO₂ catalyst was directly applied for Knoevenagel condensation, and the optimized procedure involved stirring the aldehydes and active methylene-containing compounds with Ag@TiO₂ in ethanol at 65 °C. The reaction scope was investigated for various aromatic and heterocyclic aldehydes with active methylene-containing compounds, and the isolated yields were significantly high. The reusability of the catalyst was investigated for up to five cycles, where an insignificant decrease in the catalyst's reactivity was observed. Also, the reaction could proceed in water as a solvent, and the isolated yield was 40%. Hence, this protocol features mild reaction conditions, a facile procedure, and clean reaction profiles.

Intramolecular Phosphine-Promoted Knoevenagel Based Redox-Reaction

A Knoevenagel based redox-reaction promoted by intramolecular phosphine sources is presented for the first time. The influence of different diketones, aldehydes, bases and acids was investigated. The effects of different substituents were evaluated based on their electronical influence on the diketone structure. With the obtained results a mechanism is proposed, giving information about transition states formed during the reaction, which can lead to different products. This type of an internal redox transformation with a phosphine oxide moiety remaining in the molecule after the redox reaction represents a new type of reaction.

An Overview of Metal-free Sustainable Nitrogen-based Catalytic Knoevenagel Condensation Reaction ‎

Knoevenagel condensation reaction counts as a vital condensation in organic chemistry due to the synthesis of valuable intermediates, ‎heterocycles, and fine chemicals from commercially available reactants through forming new C=C...

Highly efficient FeNP-embedded hybrid bifunctional reduced graphene oxide for Knoevenagel condensation with active methylene compounds

Novel hybrid bifunctional FeNPs/PPD@rGO for Knoevenagel condensation reaction with 100% conversion and yield.

Molybdenum carbide as an efficient and durable catalyst for aqueous Knoevenagel condensation

Molybdenum carbide showed an efficient performance for the Knoevenagel condensation in aqueous media at room temperature, affording the corresponding products in high yields within a short reaction time.

The Knoevenagel condensation using quinine as an organocatalyst under solvent-free conditions

An organocatalytic Knoevenagel condensation has been developed for the synthesis of electrophilic alkenes using natural quinine under green reaction conditions.

DABCO-catalyzed Knoevenagel condensation of aldehydes with ethyl cyanoacetate using hydroxy ionic liquid as a promoter

N-(2-Hydroxy-ethyl)-pyridinium chloride ([HyEtPy]Cl) was synthesized and explored as a novel promoter for 1,4-diazabicyclo [2.2.2] octane (DABCO)-catalyzed Knoevenagel condensation reactions, which showed better catalytic activity compared to other ionic liquid (IL) that had no hydroxyl group attached to the IL scaffold. The effect of hydrogen bond formation between the hydroxyl group of [HyEtPy]Cl and the carbonyl group of aldehyde played an important role in the Knoevenagel condensation reaction. In the [HyEtPy]Cl–H₂O–DABCO composite system, Knoevenagel condensation reactions proceeded smoothly and cleanly, and the corresponding Knoevenagel condensation products were obtained in good to excellent yields in all cases examined. This protocol provides a versatile solvent–catalyst system, which has notable advantages such as being eco-friendly, ease of work-up and convenient reuse of the ionic liquid.

N-(2-Hydroxy-ethyl)-pyridinium chloride ([HyEtPy]Cl) was synthesized and explored as a novel promoter for 1,4-diazabicyclo [2.2.2] octane (DABCO)-catalyzed Knoevenagel condensation reactions, excellent catalytic activity was obtained.

Atomic-level organization of vicinal acid-base pairs through the chemisorption of aniline and derivatives onto mesoporous SBA15

The design of novel heterogeneous catalysts with multiple adjacent functionalities is of high interest to heterogeneous catalysis. Herein, we report a method to obtain a majority of bifunctional acid-base pairs on SBA15. Aniline reacts with SBA15 by opening siloxane bridges leading to N-phenylsilanamine-silanol pairs. In contrast with ammonia treated surfaces, the material is stable under air/moisture. Advanced solid state MAS NMR (2D 1H-1H double-quantum, 1H-13C HETCOR) experiments and dynamic nuclear polarization enhanced 29Si and 15N spectra demonstrate both the close proximity between the two moieties and the formation of a covalent Si-N surface bond and confirm the design of vicinal acid-base pairs. This approach was successfully applied to the design of a series of aniline derivatives of bifunctional SBA15. A correlation between the substituent effects on the aromatic ring (Hammett parameters) with the kinetics of a model Knoevenagel reaction is observed.

Choline Chloride and Urea Based Eutectic Solvents: Effective Catalytic Systems for the Knoevenagel Condensation Reactions of Substituted Acetonitriles

The Knoevenagel condensation of aromatic aldehydes with active methylene compounds such as malononitrile, ethyl cyanoacetate, benzimidazole-2-acetonitrile and benzothiazole-2-acetonitrile proceeded very smoothly, in a reusable and cheap choline chloride and urea based deep eutectic solvents. Both reaction time and yield are satisfactory. The advantages of this catalyst are that it is readily available, biodegradable, non-toxic, low cost and is recyclable.

Ionic tagged amine supported on magnetic nanoparticles: synthesis and application for versatile catalytic Knoevenagel condensation in water

Propylamine modified with imidazolium ionic moiety grafted onto magnetic nanoparticles (MNPs) was prepared and evaluated as a catalyst for Knoevenagel condensation in water at room temperature.

Knoevenagel reaction in [MMIm][MSO₄]: synthesis of coumarins

The ionic liquid 1,3-dimethylimidazolium methyl sulfate, [MMIm][MSO₄], together with a small amount of water (the amount taken up by the ionic liquid upon exposure to air), acts efficiently as both solvent and catalyst of the Knoevenagel condensation reactions of malononitrile with 4-substituted benzaldehydes, without the need for any other solvent or promoter, affording yields of 92%–99% within 2–7 min at room temperature. When L-proline is used as an additional promoter to obtain coumarins from o-hydroxybenzaldehydes, the reaction also proceeds in high yields. Work-up is very simple and the ionic liquid can be reused several times. Some of the coumarins obtained are described for the first time.

A Facile Method for the Synthesis of 2-(3-aryl-2-cyanopropenoyl)-1-methylpyrrole catalysed by KF/Al2O3 with microwave irradiation

Knoevenagel reaction of 2-cyanoacetylpyrrole with aromatic aldehydes afforded 2-(3-aryl-2-cyanopropenoyl)-1-methylpyrrole in 81–94% yields in ethanol catalysed by KF/Al2O3 under microwave irradiation. This method has the advantages of simplicity, good yields and low costs.