Mg–Al hydrotalcites as efficient catalysts for aza-Michael addition reaction: A green protocol

Experimental Study on Restoration Materials of Newly Earthen Ruins under Different Slaking Times

The newly repaired Kaifeng City Wall has serious cracks, shedding and other issues on the surface, which constitute a significant problem. It is of great significance for the restoration of Kaifeng City Wall to explore the repair materials and techniques suitable for Kaifeng City Wall. The pH, particle gradation, compressive strength and SEM were tested on soil samples with different lime and MgO contents under different slaking times. With the increase of slaking time, the pH value first increased and then decreased. The relationship between pH value and strength showed three stages. The strength of lime-containing soil samples increased first, then decreased and then increased. The MgO content of soil samples showed an opposite trend. The particle gradation was significantly improved with increasing aging time. The main reason for the reduction of soil strength is the calcium carbonate crystals and magnesite microcracks produced by lime and MgO in the later stage of slaking.

Bicyclic 5-6 Systems: Comprehensive Synthetic Strategies for the Annulations of Pyrazolo[ 1,5-a]pyrimidines

Pyrazolopyrimidines are a privileged class of 5-6 bicyclic systems with three or four nitrogen atoms, including four possible isomeric structures. The significance of this class of compounds is that they can be applied in medical and pharmaceutical fields due to their unlimited biological aptitude, hence it is the basic skeleton of several synthetic drugs. The current review aimed to highlight all the synthetic routes that have been applied to construct the pyrazolo[1,5-a]pyrimidine ring systems up to date. The sections in this study included the synthesis of pyrazolo[1,5- a]pyrimidines by condensation reactions of 5-aminopyrazoles with each of β-diketones, 1,5-diketones, β- ketoaldehydes, α-cyanoaldehydes, β-enaminones, enamines, enaminonitriles, ethers, with unsaturated ketones, unsaturated thiones, unsaturated esters, unsaturated dienones "1,2-allenic", unsaturated aldehydes, unsaturated imines, and unsaturated nitriles. The routes adopted to synthesize this class of heterocyclic compounds were extended for ring construction from acyclic reagents and multicomponent reactions under catalytic or catalyst-free conditions.

Ultrasonic-Assisted Michael Addition of Arylhalide to Activated Olefins Utilizing Nanosized CoMgAl-Layered Double Hydroxide Catalysts

An efficient cobalt-based layered double hydroxide (LDH)-catalyzed Michael addition of an aryl halide compound onto activated olefin as a Michael acceptor is described. The synthesized catalytic materials were characterized using different techniques to investigate their physicochemical, morphological, and textural properties. The partial isomorphic substitution of magnesium by cobalt ions in the cationic sheets of the layered double hydroxide (CoMgAl-LDH) appears to be an appropriate catalyst to cause this reaction. This technique enables compound synthesis resulting from the 1,4-addition in good to excellent yields. Moreover, ultrasound was found to have beneficial effect on this reaction due to the cavitation phenomenon.

Ternary Hydrotalcites in the Multicomponent Synthesis of 4H-Pyrans

Lamellar double hydroxides (LDH) with double divalent cations were synthesized by the co-precipitation method and studied in the multicomponent synthesis of 4H-pyrans. The solids obtained were characterized by X-ray diffraction (XRD), infrared spectroscopy (FTIR), N2 adsorption isotherms, and thermogravimetric analysis (TGA). The XRD patterns confirmed the formation of LDHs in which the incorporation of Ni2+ or Co2+ improves their crystalline and textural properties. The results of catalytic activity showed that the synthesis of 4H-pyrans is favored in solvent-free conditions with the LDH–Ni catalyst, avoiding calcination processes. In addition, it was found that hydrotalcite with double divalent cations can conduct this reaction through multicomponent synthesis or by the Michael addition reaction, which can be performed by different types of basicity that depend on the composition of another divalent cation in the brucite layer or a calcination process.

5-Amino-pyrazoles: potent reagents in organic and medicinal synthesis

5-Amino-pyrazoles have proven to be a class of fascinating and privileged organic tools for the construction of diverse heterocyclic or fused heterocyclic scaffolds. This review presents comprehensively the applications of 5-amino-pyrazoles as versatile synthetic building blocks in the synthesis of remarkable organic molecules with an emphasis on versatile functionalities. Following a brief introduction of synthesis methods, planning strategies to construct organic compounds, particularly diverse heterocyclic scaffolds, such as poly-substituted heterocyclic compounds and fused heterocyclic compounds via 5-amino-pyrazoles, have been summarized. Fused heterocycles are classified as bicyclic, tricyclic, tetracyclic, and spiro-fused pyrazole derivatives. These outstanding compounds synthesized via wide variety of approaches include conventional reactions, one-pot multi-component reactions, cyclocondensation, cascade/tandem protocols, and coupling reactions. 5-Amino-pyrazoles represent a class of promising functional reagents, similar to the biologically active compounds, highlighted with diverse applications especially in the field of pharmaceutics and medicinal chemistry. Notably, this critical review covers the articles published from 1981 to 2018.

Synthesis of polycarbonate diols catalyzed by calcined hydrotalcites doped with the transition metal Ni2+

Calcined hydrotalcites doped with Ni²⁺ (HTC-Ni-T) were prepared and used as catalysts for the synthesis of polycarbonate diols (PCDLs) via transesterification between dimethyl carbonate (DMC) and 1,4-butanediol (BDO).

Layered double hydroxides as the next generation inorganic anion exchangers: Synthetic methods versus applicability

This work is the first report that critically reviews the properties of layered double hydroxides (LDHs) on the level of speciation in the context of water treatment application and dynamic adsorption conditions, as well as the first report to associate these properties with the synthetic methods used for LDH preparation. Increasingly stronger maximum allowable concentrations (MAC) of various contaminants in drinking water and liquid foodstuffs require regular upgrades of purification technologies, which might also be useful in the extraction of valuable substances for reuse in accordance with modern sustainability strategies. Adsorption is the main separation technology that allows the selective extraction of target substances from multicomponent solutions. Inorganic anion exchangers arrived in the water business relatively recently to achieve the newly approved standards for arsenic levels in drinking water. LDHs (or hydrotalcites, HTs) are theoretically the best anion exchangers due to their potential to host anions in their interlayer space, which increases their anion removal capacity considerably. This potential of the interlayer space to host additional amounts of target aqueous anions makes the LDHs superior to bulk anion exchanger. The other unique advantage of these layered materials is the flexibility of the chemical composition of the metal oxide-based layers and the interlayer anions. However, until now, this group of "classical" anion exchangers has not found its industrial application in adsorption and catalysis at the industrial scale. To accelerate application of LDHs in water treatment on the industrial scale, the authors critically reviewed recent scientific and technological knowledge on the properties and adsorptive removal of LDHs from water on the fundamental science level. This also includes review of the research tools useful to reveal the adsorption mechanism and the material properties beyond the nanoscale. Further, these properties are considered in association with the synthetic methods by which the LDHs were produced. Special attention is paid to the LDH properties that are particularly relevant to water treatment, such as exchangeability ease of the interlayer anions and the LDH stability at the solid-water interface. Notably, the LDH properties (e.g., rich speciation, hydration, and the exchangeability ease of the interlayer anions with aqueous anions) are considered in the synthetic strategy context applied to the material preparation. One such promising synthetic method has been developed by the authors who supported their opinions by the unpublished data in addition to reviewing the literature. The reviewing approach allowed for establishing regularities between the parameters: the LDH synthetic method-structure/surface/interlayer-removal-suitability for water treatment. Specifically, this approach allowed for a conclusion about either the unsuitability or promising potential of some synthetic methods (or the removal approaches) used for the preparation of LDHs for water purification at larger scales. The overall reviewing approach undertaken by the authors in this work mainly complements the other reviews on LDHs (published over the past seven to eight years) and for the first time compares the properties of these materials beyond the nanoscale.

Simple access toward 3-halo- and 3-nitro-pyrazolo[1,5-a]pyrimidines through a one-pot sequence

Herein, a regioselective, time-efficient and one-pot route for the synthesis of diversely substituted 3-halo- and 3-nitropyrazolo[1,5-a]pyrimidines in good to excellent yields through a microwave-assisted process is provided.

Recent developments in chemical reactivity of N,N-dimethylenamino ketones as synthons for various heterocycles

This review demonstrates the high number of synthetic applications of enaminones in the preparation of acyclic, carbocyclic, heterocyclic and fused heterocyclic compounds.

Simple and efficient protocol for synthesis of pyrido[1,2-a]pyrimidin-4-one derivatives over solid heteropolyacid catalysts

Aluminium exchnaged tungstophosphoric acid salts with Keggin structure (Al_xH_3−xPW₁₂O₄₀) were prepared and used as catalysts to synthesize pyrido[1,2-a]pyrimidines under mild reaction conditions.

La-modified mesoporous Mg–Al mixed oxides: effective and stable base catalysts for the synthesis of dimethyl carbonate from methyl carbamate and methanol

The incorporation of a suitable amount of La into Mg–Al mixed oxide catalysts was beneficial for the production of dimethyl carbonate.

A facile, regioselective synthesis of novel 3-(N-phenylcarboxamide)pyrazolo[1,5-a]pyrimidine analogs in the presence of KHSO4 in aqueous media assisted by ultrasound and their antibacterial activities

An environmentally benign, simple, efficient, and convenient route is described for the synthesis of novel pyrazolo[1,5-a]pyrimidine derivatives under ultrasound irradiation. Condensation of aminopyrazole 5 with formylated active proton compounds (6, 8, E-G, 12, and 15) furnished pyrazolopyrimidine (7, 9, 10, 13, and 16) in high-to-excellent yields. In comparison with conventional methods, ultrasound irradiation offers several advantages, such as shorter reaction time, higher yields, milder conditions, and environmental friendliness. The reaction is clean with excellent yields and reduces the use of solvents. X-ray crystallographic study of compound 7c confirmed the regioselectivity of the reaction. The antibacterial profile of the newly synthesized compounds was evaluated by cup and saucer method.

A facile environment-friendly one-pot two-step regioselective synthetic strategy for 3,7-diarylpyrazolo[1,5-a]pyrimidines related to zaleplon and 3,6-diarylpyrazolo[1,5-a]pyrimidine-7-amines assisted by KHSO₄ in aqueous media

3-Aminopyrazoles required for the synthesis of pyrazolo[1,5-a]pyrimidines were obtained by the reaction of enaminonitriles with hydrazine hydrate. The resulting aminopyrazoles are reacted with formylated acetophenones under reflux at [Formula: see text] assisted by KHSO[Formula: see text] in aqueous media to form regioselectively 3,7-diarylpyrazolo[1,5-a]pyrimidines and 3,6-diarylpyrazolo[1,5-a]pyrimidine-7-amines. X-ray crystallography of selected compounds 5b and 7i further confirmed the regioselective formation of these products.

One pot domino reaction accessing γ-nitroesters: synthesis of GABA derivatives

γ-Nitroesters are synthesized by the one pot domino process. GABA derivatives phenibut and baclofen were readily accessed.

Progress of the synthesis of condensed pyrazole derivatives (from 2010 to mid-2013)

Condensed pyrazole derivatives are important heterocyclic compounds due to their excellent biological activities and have been widely applied in pharmaceutical and agromedical fields. In recent years, numerous condensed pyrazole derivatives have been synthesized and advanced to clinic studies with various biological activities. In this review, we summarized the reported synthesis methods of condensed pyrazole derivatives from 2010 until now. All compounds are divided into three parts according to the rings connected to pyrazole-ring, i.e. [5, 5], [5,F 6], and [5, 7]-condensed pyrazole derivatives. The biological activities and applications in pharmaceutical fields are briefly introduced to offer an orientation for the design and synthesis of condensed pyrazole derivatives with good biological activities.

Syntheses, X-ray structures, catalytic activity and magnetic properties of two new coordination polymers of Co(ii) and Ni(ii) based on benzenedicarboxylate and linear N,N′-donor Schiff base linkers

Mixed ligand coordination polymers showing excellent catalytic activity for Knoevenagel condensation reaction.

Divergent reaction pathways for one-pot, three-component synthesis of novel 4H-pyrano[3,2-h]quinolines under ultrasound irradiation

The present paper deal with the multi-component condensation of 8-hydroxy quinoline, aromatic aldehydes, and sulfone derivatives catalyzed by p-toluenesulfonic acid for the synthesis of a series of 4H-pyrano[3,2-h]quinoline derivatives in ethanol under ultrasonic irradiations. We provide a series of quinoline derivatives containing sulfone moiety interesting for biological screening tests. The reactions were carried out under both conventional and ultrasonic irradiation conditions. In general, improvement in rates and yields were observed when reactions were carried out under sonication compared with classical silent conditions. Also, also, sonochemical reaction give different reaction pathway other than silent reaction. These remarkable effects appeared in sonicated reactions can be reasonably interpreted in terms of acoustic cavitation phenomenon. Structures of the products were established on analytical and spectral data.

Ultrasonic irradiation assisted efficient regioselective synthesis of CF3-containing pyrazoles catalyzed by Cu(OTf)2/Et3N

Background

Most of the known approaches to the synthesis of CF₃-containing organic compounds suffer from serious drawbacks. For example the starting materials required for these methods are rather difficult to obtain, or they are fairly toxic and inconvenient to work with and methods for direct fluorination and trifluoromethylation do not always allow the introduction of the CF₃-group at the required position of a molecule.

Results

An efficient and attractive regioselective synthesis of a series of novel pyrazoles containing the trifluromethyl moiety was achieved using Cu(OTf)₂/Et₃N as an efficient catalytic system under ultrasonic irradiation.

Conclusions

Cu(OTf)₂/Et₃N catalyst showed a great advantage over all the investigated catalysts, and the ultrasonic irradiation method offered high yields of pyrazoles in short reaction time compared with classical conditions. gHMBC spectra of the product were used to rationalize the observed regioselectivity.