Ultrasound assisted one-pot, three-components synthesis of pyrimido[1,2-a]benzimidazoles and pyrazolo[3,4-b]pyridines: A new access via phenylsulfone synthon

Ultrasound-Promoted preparation and application of novel bifunctional core/shell Fe3O4@SiO2@PTS-APG as a robust catalyst in the expeditious synthesis of Hantzsch esters

In this work, D-(-)-α-phenylglycine (APG)-functionalized magnetic nanocatalyst (Fe₃O₄@SiO₂@PTS-APG) was designed and successfully prepared in order to implement the principles of green chemistry for the synthesis of polyhydroquinoline (PHQ) and 1,4-dihydropyridine (1,4-DHP) derivatives under ultrasonic irradiation in EtOH. After preparing of the nanocatalyst, its structure was confirmed by different spectroscopic methods or techniques including Fourier transform infrared (FTIR) spectroscopy, energy-dispersive X-ray spectroscopy (EDS), field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and thermal gravimetric analysis (TGA). The performance of Fe₃O₄@SiO₂@PTS-APG nanomaterial, as a heterogeneous catalyst for the Hantzsch condensation, was examined under ultrasonic irradiation and various conditions. The yield of products was controlled under various conditions to reach more than 84% in just 10 min, which indicates the high performance of the nanocatalyst along with the synergistic effect of ultrasonic irradiation. The structure of the products was identified by melting point as well as FTIR and ¹H NMR spectroscopic methods. The Fe₃O₄@SiO₂@PTS-APG nanocatalyst is easily prepared from commercially available, lower toxic and thermally stable precursors through a cost-effective, highly efficient and environmentally friendly procedure. The advantages of this method include simplicity of the operation, reaction under mild conditions, the use of an environmentally benign irradiation source, obtaining pure products with high efficiency in short reaction times without using a tedious path, which all of them address important green chemistry principles. Finally, a reasonable mechanism is proposed for the preparation of polyhydroquinoline (PHQ) and 1,4-dihydropyridine (1,4-DHP) derivatives in the presence of Fe₃O₄@SiO₂@PTS-APG bifunctional magnetic nanocatalyst.

Transition-Metal-Free Dehydrogenation of Benzyl Alcohol for C-C and C-N Bond Formation for the Synthesis of Pyrazolo[3,4-b]pyridine and Pyrazoline Derivatives

A series of cascade reactions that produce a range of functionalized aromatic heterocyclic compounds with pyrazole/pyrazoline cores have been developed. The method relies on a metal-free dehydrogenative process to produce in-situ benzaldehydes. The produced benzaldehyde was then allowed to react with some other substances, including acetophenone, pyrazole amine, and phenylhydrazine. The intermediate produced from these substrates underwent several chemical processes, including electrocyclization, the aza-Diels-Alder reaction, and the formation of intramolecular C-N bonds. These positive outcomes would open up the possibility of producing biologically active pyrazolo[3,4-b]pyridine and pyrazoline derivatives through a variety of possible reactions.

Ultrasound-Assisted 1,3-Dipolar Cycloadditions Reaction Utilizing Ni-Mg-Fe LDH: A Green and Sustainable Perspective

Ultrasound-assisted synthesis of novel pyrazoles using Ni-Mg-Fe LDH as a catalyst in cyclopentyl methyl ether (CPME) is introduced. Different LDHs were tested as a catalyst for the synthesis of pyrazoles via a 1,3-dipolar cycloaddition reaction. Among them, Ni-Mg-Fe LDH was the superior catalyst for this reaction. This protocol offered high yields, a short reaction time, and a green solvent, and with the reuse of this catalyst six times with the same activity, it could be regarded as an ecofriendly, greener process. The NiMgFe LDH catalyst with the smallest particle size (29 nm) and largest surface area showed its superior efficacy for the 1,3 dipolar cycloaddition rection and can be successfully used in up to six catalytic cycles with little loss of catalytic activity. A plausible mechanism for this reaction over the Ni-Mg-Fe LDH is proposed.

Explorative Sonophotocatalytic Study of C-H Arylation Reaction of Pyrazoles Utilizing a Novel Sonophotoreactor for Green and Sustainable Organic Synthesis

The development of a mild, general, and green method for the C-H arylation of pyrazoles with relatively unreactive aryl halides is an ongoing challenge in organic synthesis. We describe herein a novel sonophotoreactor based on an ultrasonic cleaning bath and blue LED light (visible light) that induce copper-catalyzed monoarylation for pharmacologically relevant pyrazoles. The hybrid effect of ultrasonic irradiation and blue LED is discussed to interpret the observed synergistic action. A broad array of pyrazoles coupled with iodobenzene avoids expensive palladium metal or salts, and certain designed substrates were attained. Only comparatively inexpensive copper(I)iodide and 1,10-phenanthroline were used all together as the catalyst. The presented technique is a greener way to create C-H arylation of pyrazoles. It significantly reduces the amount of energy needed.

Synthesis of Novel Azo-Linked 5-Amino-Pyrazole-4-Carbonitrile Derivatives Using Tannic Acid-Functionalized Silica-Coated Fe3O4 Nanoparticles as a Novel, Green, and Magnetically Separable Catalyst

Tannic acid-linked silica-coated Fe₃O₄ nanoparticles (Fe₃O₄@SiO₂@Tannic acid) were prepared and characterized by transmission electron microscope (TEM), field emission scanning electron microscope (FE-SEM), X-ray powder diffraction (XRD), X-ray spectroscopy (EDX), vibrating sample magnetometry (VSM), and Fourier transform infrared (FT-IR) spectroscopy. Fe₃O₄@SiO₂@Tannic acid supplies an environmentally friendly procedure for the synthesis of some novel 5-amino-pyrazole-4-carbonitriles through the three-component mechanochemical reactions of synthetized azo-linked aldehydes, malononitrile, and phenylhydrazine or p-tolylhydrazine. These compounds were produced in high yields and at short reaction times. The catalyst could be easily recovered and reused for six cycles with almost consistent activity. The structures of the synthesized 5-amino-pyrazole-4-carbonitrile compounds were confirmed by ¹H NMR, ¹³C NMR, and FTIR spectra, and elemental analyses.

Chemoselective synthesis of fully substituted pyrroles via a one-pot four-component isocyanide-based reaction

Small-ring heterocycles comprising pyrrole and pyrazole are well known for their rich biological properties. In this article, an efficient green sonochemical approach was designed for the synthesis of novel, fully substituted pyrroles connected to pyrazole scaffolds via a one-pot, four-component isocyanide-based sequential reaction. This reaction was carried out using various 5-amino-pyrazoles, aldehydes, dialkyl acetylenedicarboxylates and isocyanides for the synthesis of fully functionalized pyrroles with high chemoselectivity in the presence of a catalytic amount of PTSA·H2O, in good to excellent yields under ultrasound irradiation. This waste-free (-H2O) reaction exhibited a high atom economy and step economy via creating four new bonds, including two C-N and two C-C bonds, and the formation of two five-member heterocycles which are connected in a single operation. The mechanism of this four-component domino process involved sequential imination-dipolar cyclization-[1,5]-H shift reactions. The synthesized compounds possess interesting fluorescence features, and the bioactive scaffolds might attract great interest in the fields of clinical diagnostics and biomedical research in the future.

Sonochemical synthesis of novel pyrano[3,4-e][1,3]oxazines: A green protocol

The atom-efficient and green protocol for formation of pyrano[3,4-e][1,3]oxazines utilizing dimethyl carbonate under ultrasound irradiation in a presence of KF/basic alumina was reported. We provide a novel series of pyrano[3,4-e][1,3]oxazine derivatives interesting for biological screening tests. In general, it was found that ultrasound irradiations enable the reactions to occur which could not be carried out under silent conditions. 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. This protocol offers several advantages attain many principles of green chemistry including, save energy, atom economy, clean reactions, inexpensive green reagent and use catalysts rather than stoichiometric reagents.

Efficient Synthesis of Novel 5-Phenylsulfonyl-Substituted 4,5-Dihydro-1H-Pyrazolo[3,4-b]Pyridines

An efficient method for the synthesis of novel 5-phenylsulfonyl substituted 4,5-dihydro-1H-pyrazolo[3,4-b]pyridines from 5-aminopyrazoles, aldehydes and β-ketosulfones in refluxing acetic acid is described. The X-ray crystallographic structure of the product was determined.

Copper(ii) oxide nanoparticles as a highly active and reusable heterogeneous catalyst for the construction of phenyl-1H-pyrazolo[3,4-b]pyridine derivatives under solvent-free conditions

We developed a simple and efficient method for the one-pot synthesis of phenyl-1H-pyrazolo[3,4-b]pyridine derivatives in the presence of CuO NPs under solvent-free conditions with higher yields and shorter reaction times.

Regioselective one-pot three component synthesis of chiral 2-iminoselenazolines under sonication

A one-pot multi component reaction of selenoureas, which are in situ generated from l-amino esters and isoselenocyanates, with α-bromoketone under ultrasonication.

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.

Ultrasound promoted synthesis of some novel fused pyrans

Novel fused pyrans were synthesized from the reaction of the tetrahydropyran-4-one with arylidine malononitriles. Different fused pyran derivatives were obtained from the mentioned reaction depending on type of catalyst used and type of energy used. Reactions were carried out under silent and ultrasonic conditions. In general, it was found that sometimes ultrasound irradiations change the reaction path in comparing with silent condition. In addition to improvement in reaction times, the products were obtained in high yields and their structures were determined by elemental analyses, spectral data.