PEG-SO3H as an efficient and reusable catalyst for chemoselective synthesis of 1,1-diacetates

An efficient and convenient procedure of the synthesis of 1,1-diacetates from aromatic aldehydes and acetic anhydride under mild and solvent-free conditions at room temperature,in the presence of PEG-SO₃H is reported.PEG-SO₃H acts as a catalyst and can be recovered and reused eight times without apparent loss of its catalytic activity.     

NBS as an efficient catalyst for the synthesis of 1,5-benzodiazepine derivatives under mild conditions

Various biologically important 1,5-benzodiazepine derivatives were efficiently synthesized in excellent yields using catalytic amounts of NBS (10 mol %). This inexpensive, nontoxic, and readily available catalyst efficiently catalyzes the condensation of several aromatic as well as aliphatic ketones with substituted o-phenylenediamines.     

Selenonium ionic liquid as an efficient catalyst for the synthesis of thioacetals under solvent-free conditions

Acidic ionic liquid butyl ethyl phenyl selenonium tetrafluoroborate, [BEPSe]BF₄, was successfully employed as a catalyst for the synthesis of several dithioacetals in the absence of a solvent. The method is general and selectively afforded thioacetals derived from aldehydes and ketones in good yields.     

Boric acid as an efficient catalyst for the synthesis of 1,1-diacetate under solvent-free condition

Boric acid (BO₃H₃) is an inexpensive, efficient and mild catalyst for the synthesis of 1,1-diacetate (acylal) from the various aromatic and heteroaryl aldehydes with acetic anhydride at room temperature under solvent-free condition. The present method does not involve any hazardous organic solvents or catalysts. This method gives notable advantages such as excellent chemoselectivity, mild reaction condition, short reaction times and excellent yield.     

Silica sulfate as a recyclable and efficient catalyst for Beckmann rearrangement under microwave irradiation

Silica sulfate has been proved to be an efficient and recyclable catalyst for Beckmann rearrangement of a variety of oximes in acetone under microwave irradiation. This protocol has advantages of high conversion, high selectivity, short reaction time, no environmental pollution, and simple work-up procedure.     

Choline chloride as an efficient catalyst for the synthesis of styryl-pyrazoles

An efficient and green methodology for syntheses of various styryl-pyrazoles (3) from the reaction of 2-(5-phenyl-1H-pyrazol-3-yl)acetonitriles (1) with substituted benzaldehydes (2) by the use of biodegradable, nonhazardous, naturally occurring, and inexpensive choline chloride and NaOH under an environmentally benign medium has been described.     

A novel nanomagnetic solid acid catalyst for the synthesis of new functionalized bis-coumarin derivatives under microwave irradiations in green conditions

In this study, a novel, green, environmentally friendly and magnetically heterogeneous catalyst based on the immobilization of sulfosalicylic acid onto Fe₃O₄ nanoparticles (Fe₃O₄@sulfosalicylic acid MNPs) is reported. The bis-coumarin analogs were synthesized in high yield using the reaction of 1 equivalent of aryl aldehydes with 2 equivalents of 4-hydroxycoumarin in water under microwave irradiation conditions. Scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, thermogravimetric analysis, dynamic light scattering, vibrating sample magnetometry, Fourier transform infrared spectroscopy, UV–visible absorption, and Brunauer-Emmett-Teller (BET) techniques confirmed the successful synthesis of the catalyst. The main attractive characteristics of the presented green protocol are very short reaction times (10–15 min), excellent yields, and the avoidance of hazardous or toxic reagent and solvents. Thermal durability, easy separation, and high reusability are important advantages of the new catalyst in comparison to other catalysts.     

Tungstate sulfuric acid as an efficient catalyst for the synthesis of benzoxazoles and benzothiazoles under solvent-free conditions

Tungstate sulfuric acid (TSA) has been found to be an efficient and reusable catalyst for the synthesis of benzoxazole and benzothiazole derivatives via reactions of orthoesters with o-aminophenols or o-aminothiophenols in high yields.     

Nanofiber cellulose di- and tri-acetate using ferric chloride as a catalyst promoting highly efficient synthesis under microwave irradiation

An efficient method for the generation of cellulose di- and tri-acetate nano-structures is obtained through testing ferric chloride hydrate (FeCl₃·6H₂O) as a valuable Lewis acid catalyst with acetic anhydride under microwave irradiation. Our target was to evaluate the effects of the reaction conditions on the products' properties such as surface area and particle size distribution. It was found that changes in the degree of substitution (DS), the surface area, the degree of polymerization and the particle size distribution of the products correlated with reaction conditions. Cellulose tri-acetate nanofibers with DS of 2.94 with 98.03% yield was prepared using 200 mg of FeCl₃·6H₂O, 25 ml of Ac₂O and 4 minutes of microwave irradiation. Also, cellulose di-acetate nanofibers were prepared with DS values ranged between 2.37 and 2.72 with yield ranged between 78.92 and 90.58%. The percentage of acetyl groups (Ac%) as well as the BET specific surface area, total pore volume, mean pore diameter, mono layer volume and the mean particle size of the products were determined. The maximum specific surface area obtained for the acetylated cellulose was about ten times larger than that measured for the commercial cotton cellulose and about six times larger than that of the commercial cellulose acetate. The lowest mean particle size (34.90 nm) was about eleven times smaller than the mean particle size of the commercial cellulose acetate (394 nm). The present work has proved that FeCl₃·6H₂O was a highly active catalyst for the esterification of cellulose with unexpected yields and for the formation of nanofibers with low molecular weight.     

Nanoporous aluminosilicate catalyst with 3D cage-type porous structure as an efficient catalyst for the synthesis of benzimidazole derivatives

Herein we demonstrate for the first time, the synthesis of benzimidazoles through the coupling of aldehydes with o-phenylenediamine by using highly acidic nanoporous aluminosilicate with 3D structure and cage-type pores as the catalyst. The catalyst resulted in excellent yields in short reaction times presumably due to its high acidity, large pore diameter, high surface area, and cage-type 3D porous structure.     

Scolecite as an efficient heterogeneous catalyst for the synthesis of 2,4,5-triarylimidazoles

Natural scolecite has been found as an effective catalyst for the one-pot synthesis of 2,4,5-triarylimidazole derivatives via a three component reaction using benzil or benzoin, aldehydes and ammonium acetate. This method provides several advantages such as being environmentally benign, reusable, possessing high yields with increased variations of the substituents in the product and preparative simplicity.      

Magnesium perchlorate as an efficient catalyst for the synthesis of imines and phenylhydrazones

Magnesium perchlorate has been found to be an efficient catalyst for the synthesis of imines and phenylhydrazones by the reaction of carbonyl compounds with amines and phenylhydrazine in high yields at room temperatures and in short times. The condensation of less electrophilic carbonyl compounds with poorly nucleophilic amines affords the imines in excellent yields.     

Alum as an efficient catalyst for the multicomponent synthesis of functionalized piperidines

An effective approach to the synthesis of functionalized piperidines via a one-pot multicomponent reaction of aniline, β-ketoester and aldehyde in the presence of alum as an efficient catalyst has been reported. The present procedure offers advantages such as simple workup, short reaction time and offers rapid access to a variety of functionalized piperidines.     

Silica-supported antimony(III) chloride as an efficient heterogeneous catalyst for the synthesis of aminopropenones and 3-aminopropenoates under solvent-free conditions

A convenient and efficient procedure has been developed for the synthesis of 3-aminoprop-2-en-1-ones and 3-aminoprop-2-enoates catalyzed by silica-supported antimony(III) chloride at room temperature under solvent-free conditions. The reaction takes a short time and ensures good to excellent yields of the products. Both aromatic and aliphatic amines and various 1,3-dicarbonyl compounds, including β-ketoesters and β-diketones, can be involved. Published in Russian in Zhurnal Organicheskoi Khimii, 2009, Vol. 45, No. 1, pp. 25–28. The text was submitted by the authors in English.     

Solvent-free,scalable and expeditious synthesis of benzanilides under microwave irradiation using clay doped with palladium nanoparticles as a recyclable and efficient catalyst

Benzanilide synthesis through amide bond formation was effectively carried out by palladium-doped clay catalyst using microwave irradiation under solvent-free conditions. Products were obtained with excellent yield in very short reaction time and only a small amount of the catalyst was used. The catalyst could be separated easily and recycled several times with insignificant loss in catalytic activity. No column purification was required and the products were purified by the crystallization method. The heterogeneous character of the catalyst in a ligand-free, solvent-free and base-free system supports for a practical and environmentally benign process.     

Highly efficient endoglycosidase-catalyzed synthesis of glycopeptides using oligosaccharide oxazolines as donor substrates

A highly efficient chemoenzymatic synthesis of N-glycopeptides was achieved. It was found that using synthetic oligosaccharide oxazolines, the mimics of the presumed oxazolinium ion intermediate formed in a retaining mechanism of substrate-assisted catalysis, as the donor substrates and GlcNAc-peptides as the acceptors, the endo-beta-N-acetylglucosaminidase (ENGase)-catalyzed transglycosylation gave a high yield (73-82%) of the corresponding glycopeptides in a regio- and stereospecific manner, regardless of the size of the peptide portions. The use of the oligosaccharide oxazolines as donor substrates not only expanded the substrate availability but also led to a substantial enhancement of the synthetic efficiency, compared to the use of natural N-glycans.     

Ytterbium perfluorooctanesulfonate as an efficient and recoverable catalyst for the synthesis of trisubstituted imidazoles

Synthesis of trisubstituted imidazoles was successfully accomplished using rare earth(III) perfluorooctanesulfonates (RE(OPf)₃), RE = Sc, Y, La-Lu as catalysts in fluorous solvents. Ytterbium perfluorooctanesulfonates (Yb(OPf)₃) catalyze the high efficient synthesis of trisubstituted imidazoles in fluorous solvents. By simple separation, fluorous phase containing only catalyst can be reused several times.     

Imidazole as an efficient catalyst for the synthesis of 2-amino-3-cyano-4H-chromen-4yl-phosphonates

An efficient procedure for the preparation of 2-amino-3-cyano-4H-chromen-4-yl phosphonate derivatives via a three-component reaction of salicylaldehyde, malononitrile and trialkyl phosphites or diethyl phosphite using inexpensive and environmentally friendly imidazole as organocatalyst has been reported. Beside excellent yields and easy workup, the reaction is done in an almost neutral medium.     

纳米二氧化硅负载FeCl3作为一种高效多相催化剂用于合成1,2,4-三嗪衍生物（英文）

The one‐pot synthesis of a series of 1,2,4‐triazines from the reactions of semicarbazide or thiosemi‐carbazide with various α,β‐dicarbonyl compounds under reflux conditions in a EtOH‐H2O (9:1) mixture as solvent and catalyzed by nano‐sized silica supported FeCl3 (FeCl3@SiO2) was investigat‐ed. The FeCl3 content of the catalyst was measured by atomic absorption to get the adsorption ca‐pacity. The reactions gave high yields of the product and the catalyst was easily separated and re‐used for successive reaction runs without significant loss of activity.