Tungstate sulfuric acid: preparation, characterization, and application in catalytic synthesis of novel benzimidazoles

Tungstate sulfuric acid (TSA) was prepared, characterized, and applied for direct synthesis of novel and known benzimidazoles through a condensation reaction of o-phenylenediamines with orthoesters under solvent-free conditions. TSA was characterized by powdered X-ray diffraction (XRD), X-ray fluorescence (XRF), and FTIR spectroscopy. This novel and eco-friendly method is very cheap and has many advantages such as excellent yields, recyclable and eco-friendly catalyst, and simple work-up procedure.     

Enantioselective Organocatalyzed Michael Addition of Isobutyraldehyde to Maleimides in Aqueous Media

Thiourea was introduced into (R,R)-1,2-diphenylethylenediamine as an organocatalyst to promote the reaction between isobutyraldehydes and maleimides. Enantioselective Michael addition reaction was carried out as an eco-friendly method using water as the solvent. As a result of the reaction between isobutyraldehyde and maleimide, ≥97% yield and 99% enantioselectivity were obtained at a low catalyst loading of 0.01 mol%. The solvent effect can be explained by theoretical calculations that indicate the participation of a transition state, in which the CF₃ substituent of the catalyst is a hydrogen bond activated by the surrounding water molecules. This discovery enabled the use of low catalyst loading in the organic reactions of chiral substances for pharmaceutical applications. Furthermore, a solvent effect for Michael reaction of the organocatalysts was proposed, and the organic reaction mechanisms were determined through quantum calculations.     

A mild and green chemistry approach for the synthesis of symmetrical spirooxindole derivatives

A simple and eco-friendly synthesis of the biologically important spirooxindole scaffold was done by the reaction of isatin with activated pyrazolones in the presence of a catalytic amount of p-toluenesulfonic acid in water at room temperature. A variety of symmetrical spirooxindole derivatives were obtained with excellent yields within short reaction time. This method is of great value because of its environmentally benign character, high yield, and easy handling.     

Ultrasound-assisted tandem synthesis of tri- and tetra-substituted pyrrole-2-carbonitriles from alkenes,TMSCN and N,N-disubstituted formamides

An energy-saving and eco-friendly method for the efficient construction of various tri- and tetra-substituted pyrrolecarbonitriles through ultrasound-assisted multicomponent tandem reaction of readily available alkenes, TMSCN and N,N-disubstituted formamides within 40 min under metal-, solvent-free and mild conditions was developed. The dual role of iodine (catalyst and oxidant) notably simplified the reaction conditions and reduced the chemical waste generated     

External photocatalyst-free C-H alkylation of N-sulfonyl ketimines with alkanes under visible light

A simple, practical and eco-friendly visible light-induced alkylation of N-sulfonyl ketamine under metal-, additive-, external photocatalyst-free conditions was developed. This photocatalytic method utilized low cost and abundant alkanes as the atom economy alkyl sources with H₂O₂ as the environmentally beneficial oxidant, allowing for the efficient construction of diverse valuable 4-alkylated sulfonyl ketamines. The N-sulfonyl ketamine played a dual role of reactant and photocatalyst, thus simplifying the reaction system.     

Solvent-dependent selective oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid under neat conditions

An eco-friendly and economical route for the oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) with atmospheric dioxygen as the sole oxidant under acid-, base-, metal-, and external initiator-free conditions in minimal solvent was reported. In the present reaction, the 1,2-diethoxyethylane has a dual role: reaction medium and free-radical initiator. The FDCA easily crystallizes during the reaction and was simple purified via recrystallization to provide the pure FDCA.     

Radical-mediated intramolecular C-C bond formation and the deoxygenation of alcohols under solvent-free conditions with tributyl methyl ammonium hypophosphite

A green, solvent-free protocol was developed for the radical-mediated intramolecular cyclization of haloacetals and the deoxygenation of S-methyl dithiocarbonates and cyclic thionocarbonate. This process uses tributyl methyl ammonium hypophosphite as a H-donor in the presence of triethylborane or t-butyl peroxide. This methodology provides eco-friendly reaction conditions.     

Solvent-free synthesis of quinoline derivatives via the Friedländer reaction using 1,3-disulfonic acid imidazolium hydrogen sulfate as an efficient and recyclable ionic liquid catalyst

A convenient, highly versatile and eco-friendly protocol for the synthesis of quinoline derivatives via the Friedländer reaction is presented. The method is based on the use of 1,3-disulfonic acid imidazolium hydrogen sulfate (DSIMHS) as an efficient and reusable ionic liquid catalyst. A variety of ketones afforded the substituted quinolines in excellent yields during relatively short reaction times under solvent-free conditions; the catalyst could be easily recovered and reused for several times without any appreciable loss of activity.     

One-pot four-component synthesis of 1H-pyrazolo[1,2-b]phthalazine-5,10-dione derivatives

The synthesis of 1H-pyrazolo[1,2-b]phthalazine-5,10-dione derivatives by NiCl₂-catalyzed novel one-pot four-component condensation reaction of phthalimide, hydrazine, malononitrile (or ethyl cyanoacetate), and aromatic aldehydes was reported. This work provides a simple, efficient, and eco-friendly method for the construction of pyrazolo[1,2-b]phalazine-5,10-dione derivatives.     

N,N-dimethyl-d-glucosamine as an efficient ligand for copper-catalyzed Ullmann-type coupling of N-H heterocycles with aryl halides

A new N,N-dimethyl-d-glucosamine ligand has been developed for the copper-catalyzed Ullmann-type coupling of N-H heterocycles (e.g., indoles, benzimidazoles, pyrazoles and triazoles) with aryl halides. This method was accomplished not only featuring excellent yields, mild reaction conditions and simple operation, but also showing eco-friendly and broad-spectrum substrates, and could be widely used in the construction of N-aryl heterocyclic systems.     

Green Synthesis of Indeno[1,2-b]quinoxalines Using β-Cyclodextrin as Catalyst

An efficient, mild, and green method was developed for the synthesis of indeno[1,2-b]quinoxaline derivatives via o-phenylenediamine (OPD) and 2-indanone derivatives utilizing β-cyclodextrin (β-CD) as the supramolecular catalyst. The reaction can be carried out in water and in a solid state at room temperature. β-CD can also catalyze the reaction of indan-1,2-dione with OPD with a high degree of efficiency. Compared to the reported methods, this procedure is milder, simpler, and less toxic, making it an eco-friendly alternative. In addition, the β-CD can be recovered and reused without the loss of activity.     

New applications of phosphoric acid supported on alumina (H3PO4–Al2O3) as a reusable heterogeneous catalyst for preparation of 2,3-dihydroquinazoline-4(1H)-ones, 2H-indazolo[2,1-b]phthalazinetriones,and benzo[4,5]imidazo[1,2-a]pyrimidines

An eco-friendly procedure for synthesis of 2,3-dihydroquinazoline-4(1H)-one, 2H-indazolo[2,1-b]phthalazinetrione, and benzo[4,5]imidazo[1,2-a]pyrimidine derivatives by three-component reaction, with phosphoric acid supported on alumina as catalyst, is described. Noticeable features of the method are that it is solvent-free, work-up is easy, yields are excellent, and the catalyst is reusable.     

Biosynthesis of Gold Nanoparticles by Streptomyces sp. ERI-3 Supernatant and Process Optimization for Enhanced Production

In this study, we present a simple and eco-friendly method for extracellular biosynthesis of gold nanoparticles by Streptomyces sp. ERI-3 cell-free supernatant. The research was also aimed to evaluate the effects of different reaction parameters including incubation temperature, reaction time, HAuCl₄ concentration and pH on gold nanoparticles production. The UV?CVis spectroscopy was used to monitor the formation of gold nanoparticles. The synthesized gold nanoparticles were characterized with XRD, TEM, and SEM. The average particle size ranged from 10 to 30?nm with spherical shape at optimum conditions.     

Highly efficient dialkylphosphate-mediated syntheses of hydantoins and a bicyclohydantoin under solvent-free conditions

Diversely substituted hydantoins have been synthesized by new strategy from cyanamide based precursor, that is, methyl N-cyano-N-alkyl/arylaminoacetate. Dialkylphosphates were employed as the mild reagent to hydrolyze and cyclize the substrate in one step to give quantitative yields of the desired products. Syntheses of multivalent hydantoins viz bis-hydantoin, bicyclohydantoin have potentially widened the scope and applicability of the present method. Solvent-free conditions and very easy work-up procedure make the reaction convenient and eco-friendly. Single crystal structures of some of the representative compounds are also reported.     

Polyethylene glycol (PEG-400): an efficient and recyclable reaction medium for the synthesis of pyrazolo[3,4-b]quinoline derivatives

A simple, efficient, and eco-friendly synthetic protocol has been developed via one pot three-component reaction between aldehyde, amino pyrazole, and 1,3-cyclohexanedione by using recyclable polyethylene glycol (PEG)-400 as a reaction medium. Utilizing this protocol a variety of pyrazolo[3,4-b]quinoline derivatives were synthesized in excellent yields.     

Oxidation of aromatic sulfides with molecular oxygen: Controllable synthesis of sulfoxides or sulfones

The recent development of selective oxidation of aromatic sulfides with molecular oxygen was highlighted. The sulfoxides and sulfones could be obtained by simply switching the reaction media, i.e., bis(2-butoxyethyl)ether (BBE) or poly(ethylene glycol)dimethyl ether (PEGDME). The application of the high-boiling-point polyether as an initiator and green media can eliminate the need of large quantities of additives and volatile solvents. This strategy represents an economic and eco-friendly method that could find potential applications.     

Water-acetic acid mediated an efficient and eco-friendly protocol for the one-pot synthesis of bis-isoxazolyl amino dihydro-1H-indol-4(5H)-ones under mild reaction conditions

A cost-effective and eco-friendly straightforward synthesis of new bis-isoxazolyl amino dihydro-1H-indol-4(5H)-ones is successfully achieved via one-pot three-component reaction of N-isoxazolyl enaminone, aryl glyoxal monohydrates and 4-amino-3-methyl-5-styrylisoxazoles by using water as a reaction medium and acetic acid (AcOH) as cheap and green promoter. The protocol proves to be an efficient and environmentally benign in terms of high yields, low reaction time, operational simplicity, metal-free and wide substrates scope. Most important of all, this reaction process is green.     

Sulfated polyborate catalyzed expeditious and efficient three-component synthesis of 3-methyl-4-(hetero)arylmethylene isoxazole-5(4H)-ones

A rapid and highly efficient methodology for the synthesis of 3-methyl-4-(hetero)arylmethylene isoxazole-5(4H)-ones has been developed using sulfated polyborate as a catalyst. The multicomponent reaction of an aromatic/heterocyclic aldehyde, hydroxylamine hydrochloride, and ethyl acetoacetate under a solvent free condition at 80 °C is described. This protocol has promising features for the reaction response such as shorter reaction time, easy work-up, ease of separation of pure product with high yields and simplicity in the experimental procedure. The products have been obtained in high yields (80–90%) and convenient reaction time (15–30 min). The method is operationally simple and eco-friendly.     

Preparation of ecological catalysts derived from Zn hyperaccumulating plants and their catalytic activity in Diels–Alder reaction

Zn hyperaccumulating plants Noccaea caerulescens and Anthyllis vulneraria were used as the starting material for preparation of novel Lewis ecological catalysts. Those catalysts efficiently mediate the Diels–Alder reaction. High yields, very good regio- and diastereoselectivity, low catalyst loading and the possibly of its recovery and reuse, along with mild reaction conditions, eco-friendly treatment and short reaction time, are the key advantages of the presented approach.     

A one-pot synthesis of substituted pyrido[2,3-b]indolizines

An efficient and novel approach to the synthesis of substituted pyrido[2,3-b]indolizine-10-carbonitriles was developed. These structures are practically unavailable through previously described methods. The cascade transformation involves the reaction of α,β-unsaturated carbonyl compounds with a stable dimer prepared from 1-(cyanomethyl)pyridinium chloride. The reaction was performed under reflux conditions in ethanol/water and in the presence of sodium acetate. This procedure represents a eco-friendly regioselective approach to the pyrido[2,3-b]indolizine core structure.