One-pot synthesis of multisubstituted imidazoles catalyzed by Dendrimer-PWAn nanoparticles under solvent-free conditions and ultrasonic irradiation

Abstract

An efficient, green and eco-friendly protocol has been developed for the synthesis of 2,4,5-trisubstituted and 1,2,4,5-tetrasubstituted imidazoles via one-pot condensation reaction using Dendrimer-PWA n as catalyst under solvent-free conditions or ultrasonic irradiation in excellent yields. The reactions under conventional heating conditions were compared with the ultrasonic-assisted reactions. The operational simplicity, practicability and applicability of this protocol to various substrates make it an interesting alternative to previous procedures. The present methodology offers several advantages such as excellent yields, short reaction times, a cleaner reaction, and the absence of any tedious work-up or purification. The catalyst is easily separated from the products by filtration and also exhibits remarkable reusable activity. SEM, BET and DLS of the catalyst were also investigated after each reaction cycle.Electronic supplementary material The online version of this article (

Green, cost‐effective and efficient procedure for Heck and Sonogashira coupling reactions using palladium nanoparticles supported on functionalized Fe3O4@SiO2 by polyvinyl alcohol as a highly active, durable and reusable catalyst

“…Then 0.2 mL of tetraethyl orthosilicate was slowly added to the solution and was stirred for a further 30 min. Fe 3 O 4 @SiO 2 nanospheres were collected magnetically, washed with deionized water and ethanol at room temperature three times, and finally dried at 80 °C for 10 h …”

“…Then 0.2 mL of tetraethyl orthosilicate was slowly added to the solution and was stirred for a further 30 min. Fe 3 O 4 @SiO 2 nanospheres were collected magnetically, washed with deionized water and ethanol at room temperature three times, and finally dried at 80°C for 10 h. [60,61] 2.2.3 | Preparation of Fe 3 O 4 @SiO 2 functionalized with 3-chlorotriethoxypropyl silane (Fe 3 O 4 @SiO 2 -cl NPs) A 1.0 g aliquot of Fe 3 O 4 @SiO 2 was dispersed in 20 mL of ethanol using ultrasonication followed by addition of 3 mmol of 3-chloromethoxypropylsilane (0.5 mL) under reflux conditions for 12 h. The silica-coated magnetic nanoparticles grafted with 3-chlorotriethoxypropyl silane (Fe 3 O 4 @SiO 2 -Cl) were collected by magnetic separation, washed three times with deionized water and ethanol to remove unreacted species and unwanted byproducts, and finally dried at 60°C…”

Catalytic Synthesis of 1,2,4,5‐Tetrasubstituted 1H‐Imidazole Derivatives: State of the Art

“…[120] In 2016, a series of imidazoles 15 was prepared in excellent yields and short reaction times by cyclocondensation reactions in which heteropolyacid H3PW12O40 nanoparticles immobilized onto a dendrimer polymer functionalized nanosilica was the catalyst system. [121] The reaction were carried out at 90 °C under solvent-free conditions or in EtOH at room temperature under ultrasonic irradiation. [121] (4 mmol) Nagarapu and coworkers had previously reported that tetrasubstituted imidazoles 15 are also available in high yields using potassium dodecatungstocobaltate trihydrate [K5CoW12O40•3H2O] (0.1 mol%) as catalyst for cyclo-condensation reactions carried out under microwave irradiation or classical heating conditions in which benzil (5) was a starting material.…”

Palladium nanoparticles immobilized on EDTA‐modified Fe3O4@SiO2 nanospheres as an efficient and magnetically separable catalyst for Suzuki and Sonogashira cross‐coupling reactions

“…Having specific characteristics including biocompatibility, large surface‐to‐volume ratio, low toxicity and superparamagnetism, Fe 3 O 4 nanoparticles have recently applied extensively as unique magnetic supports . Fe 3 O 4 magnetic nanoparticles have been used not only in catalysts but also in the wide range of aspects such as biosensors, ion exchange separation, magnetic fluids, magnetic data storage, magnetic inks for jet printing, environmental remediation, targeted gene therapy, drug delivery systems, detoxification of biological fluids, cell separation and biomedicine .…”