Chlorozincate(II) acidic ionic liquid: Efficient and biodegradable silylation catalyst

A practical and highly efficient silylation of alcohol and phenol derivatives with hexamethyldisilazane (HMDS) using acidic ionic liquids under mild reaction conditions is described. A series of Brønsted as well as Brønsted–Lewis acidic ionic liquids were prepared and their performance investigated for the silylation of a wide variety of alcohols and phenols with HMDS. Imidazole‐ as well as N ‐methyl‐2‐pyrrolidone‐based acidic ionic liquids have a higher catalytic activity for the protection of sensitive, hindered alcohols and phenols, thus providing an environmentally begin and versatile alternative to current acid catalysts. In addition, the acidic ionic liquids are reusable, being recovered easily and reused several times without significant deterioration in catalytic activity.     

Iron‐containing ionic liquid as an efficient and recyclable catalyst for the synthesis of C3‐substituted indole derivatives

A facile and efficient protocol for the synthesis of C3‐substituted indole derivatives has been developed under mild condition. The iron‐containing ionic liquid, 1‐(2‐hydroxyethyl)‐1,4‐diazabicyclo[2.2.2] octanylium tetrachloroferrate ([Dabco‐C₂OH][FeCl₄]) as a recyclable catalyst has been successfully used in the synthesis of trisindolines, bis(3‐indolyl) methanes and β‐indolyl alcohols for the first time. The products of trisindolines and bis(3‐indolyl) methanes are easily separated and purified without chromatographic technique. The catalyst was recycled six times without significant activity loss.     

Synthesis and characterization of a novel organic–inorganic hybrid salt and its application as a highly effectual Brønsted–Lewis acidic catalyst for the production of N,N′‐alkylidene bisamides

In this research, a novel organic–inorganic hybrid salt, namely, N¹,N¹,N²,N²‐tetramethyl‐N¹,N²‐bis(sulfo)ethane‐1,2‐diaminium tetrachloroferrate ([TMBSED][FeCl₄]₂) was prepared and characterized by Fourier‐transform infrared spectroscopy (FT‐IR), energy‐dispersive X‐ray spectroscopy (EDX), elemental mapping, field emission scanning electron microscopy (FE‐SEM), X‐ray diffraction (XRD), thermal gravimetric (TG), differential thermal gravimetric (DTG), and vibrating‐sample magnetometry (VSM) analyses. Catalytic activity of the hybrid salt was tested for the synthesis of N,N′‐alkylidene bisamides through the reaction of benzamide (2 eq.) and aromatic aldehydes (1 eq.) under solvent‐free conditions in which the products were obtained in high yields and short reaction times. The catalyst was superior to many of the reported catalysts in terms of two or more of these factors: the reaction medium and temperature, yield, time, and turnover frequency (TOF). [TMBSED][FeCl₄]₂ is a Brønsted–Lewis acidic catalyst; there are two SO₃H groups (as Brønsted acidic sites) and two tetrachloroferrate anions (as Lewis acidic sites) in its structure. Highly effectiveness of the catalyst for the synthesis of N,N′‐alkylidene bisamides can be attributed to synergy of the Brønsted and Lewis acids and also possessing two sites of each acid.     

Effective Methods for the Synthesis of N‐Methyl β‐Amino Acids from All Twenty Common α‐Amino Acids Using 1,3‐Oxazolidin‐5‐ones and 1,3‐Oxazinan‐6‐ones

N‐Methyl β‐amino acids are generally required for application in the synthesis of potentially bioactive modified peptides and other oligomers. Previous work highlighted the reductive cleavage of 1,3‐oxazolidin‐5‐ones to synthesise N‐methyl α‐amino acids. Starting from α‐amino acids, two approaches were used to prepare the corresponding N‐methyl β‐amino acids. First, α‐amino acids were converted to N‐methyl α‐amino acids by the so‐called ‘1,3‐oxazolidin‐5‐one strategy’, and these were then homologated by the Arndt–Eistert procedure to afford N‐protected N‐methyl β‐amino acids derived from the 20 common α‐amino acids. These compounds were prepared in yields of 23–57% (relative to N‐methyl α‐amino acid). In a second approach, twelve N‐protected α‐amino acids could be directly homologated by the Arndt–Eistert procedure, and the resulting β‐amino acids were converted to the 1,3‐oxazinan‐6‐ones in 30–45% yield. Finally, reductive cleavage afforded the desired N‐methyl β‐amino acids in 41–63% yield. One sterically congested β‐amino acid, 3‐methyl‐3‐aminobutanoic acid, did give a high yield (95%) of the 1,3‐oxazinan‐6‐one ( 65 ), and subsequent reductive cleavage gave the corresponding AIBN‐derived N‐methyl β‐amino acid 61 in 71% yield (Scheme 2). Thus, our protocols allow the ready preparation of all N‐methyl β‐amino acids derived from the 20 proteinogenic α‐amino acids.     

HAp‐encapsulated γ‐Fe2O3‐supported dual acidic heterogeneous catalyst for highly efficient one‐pot synthesis of benzoxanthenones and 3‐pyranylindoles

A novel method is reported for the synthesis of benzoxanthenone and 3‐pyranylindole derivatives via one‐pot three‐component reactions using a newly synthesized HAp‐encapsulated γ‐Fe₂O₃‐supported dual acidic heterogeneous catalyst, as a reusable and highly efficient nanocatalyst. In this protocol the use of the nanocatalyst provided a green, useful and rapid method to generate products in short reaction times (4–20 min) and in excellent yields (87–96%). The paramagnetic nature of the catalyst provided a simple, trouble‐free and facile approach for the separation of the catalyst by applying an external magnet, and it could be used in eight cycles without significant loss in catalytic efficiency.     

Highly efficient and green approach for the synthesis of spirooxindole derivatives in the presence of novel Brønsted acidic ionic liquids incorporated in UiO‐66 nanocages

An efficient and green approach is reported for the rapid synthesis of spirocyclic 2‐oxindole using triethylenediamine or imidazole Brønsted acidic ionic liquids supported in Zr metal–organic framework (TEDA/IMIZ‐BAIL@UiO‐66) as a novel, superior and retrievable heterogeneous catalyst under ultrasonic irradiation. Heterocyclic compounds including pyrido[2,3‐d:6,5‐d′]dipyrimidines and indeno[2′,1′:5,6]pyrido[2,3‐d]pyrimidines were obtained by the one‐pot condensation reaction of 6‐amino‐1,3‐dimethyluracil, isatins and cyclic 1,3‐diketone (barbituric acid or 1,3‐indanedione). The reusability of the catalyst, low catalyst loading, short reaction times, excellent yields, simple work‐up, and use of sonochemical procedure as a mild process and an alternative energy source are some of the advantages of this method. Furthermore, the novel heterogeneous nanocomposite was fully characterized using various techniques.     

Postsynthetic modification of IRMOF‐3 with a copper iminopyridine complex as heterogeneous catalyst for the synthesis of 2‐aminobenzothiazoles

A copper iminopyridine complex has been immobilized on to a metal–organic framework (MOF) through postsynthetic modification of IRMOF‐3. The modified MOFs were fully demonstrated by using a variety of methods, and the structural integrity of the modified MOFs has been confirmed by powder X‐ray diffraction (XRD). Furthermore, it was shown that the modified IRMOF‐3 can act as an efficient solid catalyst for the synthesis of 2‐aminobenzothiazoles via the reaction of 2‐iodoanilines with isothiocyanates in a heterogeneous manner. Moreover, the catalyst could be facilely separated from the reaction mixture and reused for six consecutive cycles without significant degradation in catalytic activity. Copyright © 2014 John Wiley & Sons, Ltd.     

Brønsted acidic ionic liquid as an efficient and reusable catalyst for one-pot synthesis of 1-amidoalkyl 2-naphthols under solvent-free conditions

A mild and efficient method has been developed for the preparation of amidoalkyl naphthols from condensation of aldehydes with amides or urea and 2-naphthol in the presence of a catalytic amount of Brønsted acidic ionic liquid ([TEBSA][HSO₄]) under thermal solvent-free conditions. High yields, short reaction time, easy work-up and reusability of the catalyst are advantages of this procedure.     

Biguanidine‐functionalized chitosan to immobilize palladium nanoparticles as a novel,efficient and recyclable heterogeneous nanocatalyst for Suzuki–Miyaura coupling reactions

Biguanidine‐functionalized chitosan was synthesized and combined with palladium nanoparticles to yield a recyclable, environmentally benign, heterogeneous catalytic system for the Suzuki–Miyaura C–C coupling reaction. The catalyst was characterized using various techniques. The catalyst was used in Suzuki cross‐coupling reactions of various aryl halides, including less reactive chlorobenzenes, with phenylboronic acid to give biaryls without any additive or ligand. A reusability test demonstrated that the catalyst was highly efficient even after six runs. Solid‐phase poisoning and leaching tests indicated that the catalyst has a heterogeneous nature. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis of 5‐substituted 1H‐tetrazoles using a recyclable heterogeneous nanonickel ferrite catalyst

An efficient method was developed for the [2 + 3] cycloaddition of sodium azide with nitriles to afford 5‐substituted 1H‐tetrazoles using nanonickel ferrite (NiFe₂O₄) as an effective heterogeneous catalyst in dimethylformamide. The main advantages of this method are high yields, simple methodology and easy work‐up. The catalyst can be recovered and reused for several cycles with predictable activity. Copyright © 2015 John Wiley & Sons, Ltd.     

Green synthesis of TiO2 nanoparticles as an efficient heterogeneous catalyst with high reusability for synthesis of 1,2‐dihydroquinoline derivatives

Nano materials find wide applications due to their behavior at nano scale. TiO₂ nanoparticles (TiO₂ NPs) was synthesized using Neem leaf extract. This is simple, rapid, eco‐friendly, cheaper and green tools for TiO₂ NPs synthesis using agricultural waste at lower applied temperature. Characterization of the extracted TiO₂ NPs was confirmed by XRD, SEM, EDAX, TEM, HR‐TEM, SAED, and FT‐IR, respectively. The catalytic activity of TiO₂ NPs was investigated in synthesis of 1,2‐dihydroquinoline derivatives with excellent yields and low cost. Purification of the synthesized 1,2‐dihydroquinoline derivatives carried out by easy work‐up of non‐chromatographic methods.     

Copper@PMO nanocomposites as a novel reusable heterogeneous catalyst for microwave‐assisted green synthesis of β‐hydroxy‐1,2,3‐triazoles through experimental design protocol

A microwave‐assisted multicomponent reaction was used to prepare a series of β‐hydroxy‐1,2,3‐triazoles in the presence of copper@PMO nanocomposites as a catalyst. Box–Behnken design and response surface methodology were used to optimize the influencing parameters such as catalyst content, reaction time and microwave power, being an economical way of obtaining the optimal reaction conditions based on restricted number of experiments. Aqueous reaction medium, easy recovery of catalyst, efficient recycling and high stability of the catalyst render the protocol sustainable and economic. Copyright © 2015 John Wiley & Sons, Ltd.     

Copper(I) oxide nanoparticles supported on magnetic casein as a bio‐supported and magnetically recoverable catalyst for aqueous click chemistry synthesis of 1,4‐disubstituted 1,2,3‐triazoles

Copper(I) oxide nanoparticles supported on magnetic casein (Cu₂O/Casein@Fe₃O₄NPs) has been synthesized as a bio‐supported catalyst and was characterized using powder X‐ray diffraction, transmission electron microscopy, energy dispersive X‐ray and Fourier transform infrared spectroscopies, thermogravimetric analysis and inductively coupled plasma optical emission spectrometry. The catalytic activity of the synthesized catalyst was investigated in one‐pot three‐component reactions of alkyl halides, sodium azide and alkynes to prepare 1,4‐disubstituted 1,2,3‐triazoles with high yields in water. The reaction work‐up is simple and the catalyst can be magnetically separated from the reaction medium and reused in subsequent reactions.     

Evaluation of the Initial Stages of Gas‐Phase Ethylene Polymerizations with a SiO2‐Supported Ziegler–Natta Catalyst

The very early stages of gas‐phase ethylene polymerization on an SiO₂‐supported Ziegler–Natta catalyst were studied with the help of a short‐stop reactor. The short‐stop‐reactor‐based technique was useful in studying nascent polymerization, providing insights at very short, controlled times into important phenomena regarding catalyst fragmentation and the activation and deactivation of catalyst sites that take place during the very early stages of the reaction. Experimental results indicate that the growth of the polymer chains occurs at unsteady conditions during the initial stages of the polymerization. Hydrogen has a strong influence on the initial kinetics, leading to a significant decrease of polymerization activity. Polymer crystallinity increases with the reaction time, probably due to the formation of long chains with a high degree of crystallinity.

     

NbCl5: an efficient catalyst for one‐pot synthesis of α‐aminophosphonates under solvent‐free conditions

NbCl₅ has been found to be a very effective catalyst for the synthesis of a variety of α‐aminophosphonates through the Kabachnik–Fields reaction of carbonyl compound, amine and diethyl phosphite under solvent‐free conditions. Copyright © 2010 John Wiley & Sons, Ltd.     

A highly selective synthesis of 1‐substituted (E)‐buta‐1,3‐dienes with 4,4,5,5‐tetramethyl‐2‐vinyl‐1,3,2‐dioxaborolane as building block

Highly selective synthesis of 1‐substituted (E)‐buta‐1,3‐dienes via palladium‐catalyzed Suzuki–Miyaura cross‐coupling of (E)‐alkenyl iodides with 4,4,5,5‐tetramethyl‐2‐vinyl‐1,3,2‐dioxaborolane ( 1 ) is reported. The vinylboronate pinacol ester ( 1 ) acts as a vinyl building block to show high chemoselectivity for the Suzuki–Miyaura pathway versus Heck coupling in the presence of biphasic conditions (Pd(PPh₃)₄, aqueous K₂CO₃, toluene and ethanol). Copyright © 2014 John Wiley & Sons, Ltd.     

Porphyrin‐based polymer‐supported palladium as an excellent and recyclable catalyst for Suzuki–Miyaura coupling reaction in water

A porphyrin‐based polymer with high surface area was synthesized using 5,10,15,20‐tetraphenylporphyrin through a one‐pot Friedel–Crafts alkylation reaction. Pd(II) was successfully supported on this polymer. This strategy provides an easy approach to produce highly stable Pd–porphyrin‐based polymer. The resulting Pd catalyst was characterized using Fourier transform infrared and X‐ray photoelectron spectroscopies, thermogravimetric analysis, scanning and transmission electron microscopies and N₂ adsorption–desorption measurements. This porphyrin‐based polymer‐supported Pd was used as a heterogeneous catalyst for Suzuki–Miyaura coupling reaction in water. The results demonstrated that this Pd catalyst indeed exhibited excellent catalytic activity and recycling performance in water, even for inactive aryl chloride substrate. A new heterogeneous strategy for catalyzing the Suzuki–Miyaura reaction in water is provided.     

Polyoxometalate immobilized on MOF‐5 as an environment‐friendly catalyst for the synthesis of poly‐functionalized 3‐pyrrolin‐2‐ones

A polyoxometalate immobilized on MOF‐5 (POM/MOF‐5) material has been synthesized and evaluated for the diversity‐oriented synthesis of poly‐functionalized 3‐pyrrolin‐2‐ones via pseudo‐four‐component reaction between dialkyl acetylenedicarboxylate, amines, and aldehyde. The catalyst can be separated from the reaction mixture and reused at least five times with superior activity.     

酸性离子液体催化合成三吲哚甲烷化合物

在酸性离子液体催化下,通过吲哚及其衍生物和吲哚甲醛反应合成了一系列三吲哚甲烷化合物。[hmim]HSO₄/EtOH 对于该反应来说,是一个高效、绿色的催化体系。