Microwave-assisted Reaction Conditions Research Articles

Microwave-assisted synthesis of 4,6-dihydroxyaurone derivatives

In this study, the authors described the evaluation of microwave-assisted reaction conditions for the synthesis of 4,6-dihydroxyaurone derivatives, including synthesis of 2’,4’,6’-trihydroxychloroacetophenone (50 W, 65°C and 30 min); synthesis of 4,6-dihydroxybenzofuran-3(2H)-one (50 W, 60°C and 5 min), and synthesis of 4,6-dihydroxyaurone (50 W, 80°C and 20-40 min). The optimum procedure was applied to prepare 4,6-dihydroxyaurone derivatives with different substituents on the benzylidene ring.

Heterocyclic androstane and estrane d-ring modified steroids: Microwave-assisted synthesis, steroid-converting enzyme inhibition, apoptosis induction, and effects on genes encoding estrogen inactivating enzymes

d-ring–fused and d-homo lactone compounds in estratriene and androstane series were synthesized using microwave-assisted reaction conditions. Microwave-irradiated synthesis methods were convenient and effective, and provided high yields with short reaction times. Their inhibition of C17,20-lyase and 17β-hydroxysteroid dehydrogenase type 1 (17β-HSD1) activities were studied in in vitro enzyme assays. d-ring–fused triazolyl estrone analog 24 showed potent inhibition of NADH-complexed 17β-HSD1, with a binding affinity similar to that of the substrate estrone; its inhibition against NADPH-complexed 17β-HSD1 was markedly weaker. Compound 24 also significantly and selectively reduced proliferation of cancer cell lines of gynecological origin. This estrane triazole changed the cell cycle and induced apoptosis of HeLa, SiHa, and MDA-MB-231 cancer cells, measured by both increased subG1 fraction of cells and activation of caspase-independent signaling pathways. A third mode of anti-estrogenic action of 24 saw increased mRNA expression of the SULT1E1 gene in HeLa cells; in contrast, its 3-benzyloxy analog 23 increased mRNA expression of the HSD17B2 gene, thus showing pronounced pro-drug anti-estrogenic activity. Estradiol-derived d-ring triazole compound 24 thus acts at the enzyme, gene expression and cellular levels to decrease the production of active estrogen hormones, demonstrating its pharmacological potential.

Novel piperazine and morpholine substituted quinolines: Selective synthesis through activation of 3,6,8-tribromoquinoline, characterization and their some metabolic enzymes inhibition potentials

Regioselective routes are described for convenient preparation of novel piperazine/morpholine substituted quinoline derivatives at C-3, C-6 and C-8 starting with 3,6,8-tribromoquinoline (6) by nucleophilic substitution via conventional heating or microwave assisted reaction conditions. 3,6,8-Tribromoquinoline (6) was treated with piperazine and morpholine under microvawe irradiation, which selectively furnished 3-mopholinyl and 3-piperazinyl quinoline derivatives 7 and 8 in yields of 58% and 60%, respectively. On the other hand, the activation of benzene cycle of quinoline by nitration of 3,6,8-tribromoquinoline, giving 5-nitro-3,6,8-tribromoquinoline (18) in quantitative yield, was enabled. Then, the bromines at C-6 and C-8 were selectively exchanged by morpholine and piperazine via SNAr reactions. Thus, 6,8-dimopholinylquinoline (22) and 5-nitro-6,8-dipiperazinylquinoline (24), biologically valuable derivatives, were prepared in high yields (82% and 72%, respectively). The synthesized compounds were fully characterizated by 1H NMR, 13C NMR, 2D NMR, XRD, HRMS and IR spectra. The novel molecules had effective inhibition profiles against some metabolic enzymes. Also, they have the potential of drug candidates to treat of some diseases including glaucoma, epilepsy, Alzheimer’s disease (AD), leukemia, and type-2 diabetes mellitus (T2DM).

P-TSA Catalyzed One-Pot Synthesis of Some Novel Bis(Hexahydroacridine-1,8-Diones) and Bis(Tetrahydrodipyrazolo[3,4-b:4′,3′-e]Pyridines) Derivatives

A simple, efficient and ecofriendly procedure has been developed for the synthesis of bis(hexahydroacridine-1,8-diones) and bis(tetrahydrodipyrazolo[3,4-b:4′,3′-e]pyridines) derivatives using p-TSA as catalyst under microwave-assisted reaction conditions as well as under conventional heating.

Targeted synthesis of a polypyridyl polyoxometalate coordination complex using microwave-assisted reaction conditions

In this article, we build upon our recent efforts that have focused on demonstrating the value of microwave-assisted synthesis in polyoxometalate (POM) chemistry. Herein, we report for the first time a microwave-assisted approach that enabled the facile preparation and crystallization of a large POM-containing coordination complex. The judicious selection and reaction of a sparingly water-soluble transition-metal-substituted polyanion (TMSP) salt with the tritopic ligand 2,4,6-tris(4-pyridyl)-1,3,5-triazine (TPT) in a mixed solvent system under moderately forcing conditions yields Ba9[(BIIIWVI11O39CoIII)3(C18H12N6)]·38H2O in moderate yield. Crystallographic analysis reveals significant intermolecular interactions between the organic ligand and neighbouring polyanions, predominantly C-H...O(water) in nature; meanwhile, the solvated regions of the crystal show significant disorder. To supplement the crystallographic study, combustion analysis, and IR and 1H NMR spectroscopic analyses were conducted, revealing good bulk purity and the stability of the complex in aqueous media.

A new approach in functionalization of carbon nanoparticles for optoelectronically relevant carbon dots and beyond

Carbon dots (CDots), generally small carbon nanoparticles with surface passivation by a soft corona-like layer of mostly organic species, have been actively pursued for potential applications in optoelectronics, including various functions that have been served by some popular fullerene derivatives. For the preparation of CDots, chemical functionalization of pre-processed and selected small carbon nanoparticles by organic molecules, so far mostly molecules with primary and secondary amine groups, has been an effective method. In this study, carbon nanoparticles were functionalized by N-ethylcarbazole (NEC) under microwave-assisted reaction conditions for NEC-CDots, analogous but with advantages to the CDots of surface functionalization by poly(N-vinylcarbazole) (PVK, which holds a special place in optoelectronics). NEC molecules can apparently be activated under the reaction conditions for reactive functionalities such as radicals to bind to surface carbons of the nanoparticles, consistent with the observed high stability of NEC-CDots. These dots, likely with a unique surface passivation scheme, exhibited optical properties and photoinduced redox characteristics similar to those found in other high-performance CDots. The potentially broad applicability of the new functionalization approach is discussed, so are implications of the unique surface passivation of carbon nanoparticles by the carbazole moieties.

Non-Aqueous Microwave-Assisted Syntheses of Deca- and Hexa-Molybdovanadates.

We report a new approach for the synthesis of heterohexa- and heterodecametalates via the use of non-aqueous, microwave-assisted reaction conditions. The two novel molybdovanadates have been isolated and characterized in the solid and solution states using single-crystal X-ray diffraction, FT-IR, UV/Vis, multinuclear NMR spectroscopy, and ESI-MS. The relative stabilities of the possible structural isomers were probed using dispersion-corrected DFT calculations for both polyoxometalate systems.

Bromination and Diazo-Coupling of Pyridinethiones; Microwave Assisted Synthesis of Isothiazolopyridine, Pyridothiazine and Pyridothiazepines

Isothiazolopyridines, pyridothiazines and pyridothiazepines are important compounds that possess valuable biological activities. This paper reports on the synthesis of these compounds using both conventional chemical methods and modern microwave techniques. 3-Bromo-6-hydroxy-4-methyl-2-thioxo-2,3-dihydropyridine-3-carboxamide, 5-arylazo-6-hydroxy-4-methyl-2-thioxo-1,2-dihydropyridine-3-carboxamides, 3,5-bis-arylazo-6-hydroxy-4-methyl-2-thioxo-2,3-dihydropyridine-3-caboxamide, 4-methyl-2,3,6,7-tetra-hydroisothiazolo[5,4-b]-pyridine-3,6-dione, 2,2'-(methylene-bis-(sulfanediyl))bis(4-methyl-6-oxo-1,6-dihydropyridine-3-carboxamide), 2-hydroxy-5-methyl-4H-pyrido[3,2-e][1,3]-thiazine-4,7(8H)-dione and 2-arylmethylene-8-hydroxy-6-methyl-2,3,4,5-tetrahydropyrido-[3,2-f][1,4]thiazepine-3,5-diones have been prepared from 6-hydroxy-4-methyl-2-thioxo-2,3-dihydropyridine-3-carboxamide. Some of these compounds were prepared using microwave-assisted reaction conditions, that provided higher yields in shorter times than the conventional methods.

The influence of microwave heating on the texture and catalytic properties of oxidized multi-walled carbon nanotubes

The influence of microwave heating on the catalytic performance of oxidized multi-walled carbon nanotubes (OMWCNTs) in oxidative dehydrogenation of ethylbenzene (ODEB) was investigated. OMWCNTs were characterized by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) before and after the catalytic reaction. The highest yield of ∼60% styrene was achieved under microwave-assisted reaction conditions. The significant amount of high disordered amorphous carbon was observed on the surface of OMWCNTs after the conventionally-heated reaction, while the treatment of the catalyst under microwave-assisted reaction conditions resulted in the formation of new layers of surface sp2-carbon. Moreover, the formation of carbonyl groups which are responsible for the dehydrogenation power of the catalyst was observed on the surface of OMWCNTs after the reaction in microwave oven only.

Microwave-assisted catalytic oxidative dehydrogenation of ethylbenzene on iron oxide loaded carbon nanotubes

The catalytic performance of multi-walled carbon nanotubes (MWCNTs) modified by iron oxide has been investigated for oxidative dehydrogenation of ethylbenzene in an integral fixed-bed reactor conventionally-heated and under microwave-assisted conditions. The morphology and microstructural characteristics of the obtained composites before and after the catalytic reaction were characterized by transmission electron microscopy and X-ray diffraction. The content 3wt.% of iron oxide supported on MWCNTs was found optimal in respect of the ethylbenzene conversion and styrene selectivity. All prepared composites were found more selective in a microwave field in the temperature range 380–450 °C. The transformation of Fe 2O 3 into Fe nanocrystals encapsulated by polyhedral graphite shells was observed only under microwave-assisted reaction conditions.

New Preparation and Purification Methods for Metallo-Supramolecular Block Copolymers

The bis-complex formation of two terpyridine-modified polymers using microwave assisted reaction conditions was investigated in detail. In order to construct a heteroleptic block copolymer polystyrene, which was prepared by nitroxide-mediated radical polymerization (NMRP), and a commercial available poly(ethylene oxide) were used. These studies include the influence of temperature, reaction time, concentration and the use of different solvent mixtures on complexation. The conversion was determined by GPC measurements. The amphiphilic metallo-supramolecular block copolymers were investigated towards their formation of micellar aggregates in water. Other characterization techniques include 1H-NMR, UV/vis spectroscopy, dynamic light scattering (DLS), atomic force spectroscopy (AFM) and transmission electron microscopy (TEM) techniques.

Synthesis of Pyridinyl-Pyrimidines via Pd-Catalyzed Cross-Coupling Reactions: A Comparison of Classical Thermal and Microwave Assisted Reaction Conditions

The Negishi cross-coupling reaction was used for the synthesis of pyridinyl-pyrimidines utilizing classical thermal or microwave assisted conditions. The organozinc substrates were prepared from 2-fluoro-4-iodopyridine byconventional lithiation chemistry and subsequent transmetalation with ZnCl 2 or ZnI 2 . Two different catalysts - Pd(PPh 3 ) 4 and Pd/C - were investigated for their ability to facilitate the cross coupling process with 2,4-dichloropyrimidine. We found that distribution and yield of desired compounds and possible by-products highly depend on the type of energy input. In contrast to thermal conditions, the microwave assisted method allowed efficient access to di-coupled compounds.