Microwave-assisted cyclocondensation of hydrazine derivatives with alkyl dihalides or ditosylates in aqueous media: syntheses of pyrazole, pyrazolidine and phthalazine derivatives

Ju, Yuhong; Varma, Rajender S.

doi:10.1016/j.tetlet.2005.07.018

Cited by 71 publications

(20 citation statements)

References 30 publications

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“…The selective absorption of MWs by polar molecules and intermediates in a multiphase system could substitute as a phase transfer catalyst without using any phase transfer reagent, thereby providing the observed acceleration, as has been observed for ultrasonic irradiation (49,50). The experimental observation is consistent with the mechanistic postulation wherein the polar transition state of the reaction is favored by MW irradiation with respect to the dielectric polarization nature of MW energy transfer (47, 48,51). In large scale experiments, the phase separation of the desired product in either solid or liquid form from the aqueous medium can facilitate product purification by simple filtration or decantation instead of tedious column chromatography, distillation, or extraction processes, which eventually reduces the usage of volatile organic solvent required for extraction or column chromatography.…”

Section: Microwave-assisted Reactions In Aqueous Mediumsupporting

confidence: 86%

“Greener” chemical syntheses using mechanochemical mixing or microwave and ultrasound irradiation

Varma

2007

Green Chemistry Letters and Reviews

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Various emerging ''greener'' strategic pathways, researched primarily in the author's own laboratory, are summarized. They include solvent-free mechanochemical methods that involve the use of hypervalent iodine reagents at room temperature for the synthesis of heterocyclic entities, and useful conversion of ketones into b-keto sulfones and their a-tosyloxy derivatives in high yields. A solvent-free approach that involves microwave (MW) exposure of neat reactants (undiluted) catalyzed by the surfaces of less-expensive and recyclable mineral supports, such as alumina, silica, clay, or ''doped'' surfaces, is described; it is applicable to a wide range of cleavage, condensation, cyclization, rearrangement, oxidation, and reduction reactions, including rapid one-pot assembly of heterocyclic compounds from in situ generated reactive intermediates. The strategy is adaptable to multi-component reactions, e.g. Ugi and Biginelli reactions, for rapid assembly of a library of compounds. Synthesis of a wide variety of significant precursors and intermediates, namely enones, imines, enamines, nitroalkenes, and oxidized sulfur species, is possible and their value in concise MW synthesis of 2-aroylbenzofurans and thiazole derivatives is illustrated. Ultrasound-and MW-assisted solventless preparation of ionic liquids and their application in alkylation and metal-catalyzed multi-component reactions are described. With a view to consume greenhouse gas, carbon dioxide (CO 2 ), efficient reaction of epoxides with CO 2 provides ready access to cyclic carbonates using only a catalytic amount of recyclable indium-based ionic liquid. MW heating in aqueous reaction media enables expeditious N-alkylation reactions of amines and hydrazines to afford a series of heterocyclic ring systems, such as N-azacycloalkanes, 4,5-dihydropyrazoles, and pyrazolidines. A general and expeditious MW-enhanced nucleophilic substitution approach uses easily accessible starting materials such as halides or tosylates in reaction with alkali azides, thiocyanates, or sulfinates in the absence of any phase transfer catalyst to produce azides, thiocyanates, and sulfones, respectively, wherein a variety of reactive functional groups are tolerated. A three-component condensation (MCC) approach for the synthesis of useful 2-amino-2-chromenes is described using a recyclable nanosized magnesium oxide catalyst in aqueous poly (ethylene glycol) (PEG) medium at room temperature. A general greener approach to shape-selective generation of nanomaterials is summarized including their potential application as nanocomposites.

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Section: Microwave-assisted Reactions In Aqueous Mediumsupporting

confidence: 86%

“Greener” chemical syntheses using mechanochemical mixing or microwave and ultrasound irradiation

Varma

2007

Green Chemistry Letters and Reviews

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“…IR spectra were recorded on a FT-IR JASCO 6100 instrument in KBr phase. 1 H NMR and 13 C NMR spectra were recorded on a Varian spectrometer (300 MHz) in DMSO-d6 as solvent, using TMS as internal standard and chemical shifts are expressed as δ ppm. The mass spectra were recorded by ISQ LT single quadrupole mass spectrometer.…”

Section: Methodsmentioning

confidence: 99%

“…[1][2][3][4][5][6][7][8][9][10][11] In this respect and various approaches for the preparation of these privileged structures with drug-like properties have been developed on various synthetic strategies. Pyrimidines, as the most important nitrogen-containing heterocyclic compounds, are of chemical and pharmacological interest.…”

Section: Introductionmentioning

confidence: 99%

Michael Cyclization of Polarized Systems: Synthesis and in vitro Anti-Diabetic Evaluation of Some Novel Pyrimidine, Pyridine, Pyrazole and Pyrazolo[3,4-b ]pyridine Derivatives

2017

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Various interesting heterocycle skeletons were synthesized via Michael type addition reaction with 1,2; 1,3-bidentate nitrogen and carbon nucleophiles. Cycloaddition of different α,β-unsaturated systems afforded bromopyrimidinone 3/5, bromothiazine 4 and bromopyrazole 6a/6b pyrazole-1-carboxylate 8, pyridinylmethanone 9, nicotinonitrile 10, pyrazolopyridine 11a/11b, pyran-3-carbonitrile 12/13, chromenopyridine 14 and N-butyrylpyrazolyl-1-butanone 15 derivatives. The structures of the synthesized compounds were elucidated based on IR, NMR and mass spectral analyses. Group of the newly synthesized compounds were screened for their anti-diabetic activities, whereas compounds 8 and 11b exhibited promising anti-diabetic activities at micro molar concentration against α-glucosidase inhibitor with IC50 values ranging between 13.80-500 μM. On the other hand compound 10 showed a week effect as compared to the standard anti-diabetic agent.

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“…The reactions proceed via double N-alkylation of primary amines and hydrazine derivatives (Scheme 19) with readily available alkyl dihalides (or ditosylates), thus providing facile entry to important classes of building blocks in natural products and pharmaceuticals. [41][42][43] This MW-accelerated general approach shortened the reaction time significantly and utilized readily available amines and hydrazines with alkyl dihalides or ditosylates to assemble two C-N bonds in a simple S N 2-like sequential heterocyclization experimental protocol which has never been fully realized under conventional reaction conditions. The strategy circumvents multi-step reactions and functional group protection/ deprotection sequences, and eliminates the use of expensive phase transfer and transition metal catalysts.…”

Section: Scheme 14mentioning

confidence: 99%

Aqueous microwave chemistry: a clean and green synthetic tool for rapid drug discovery

2008

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The development of "Greener Organic Chemistry" is due to the recognition that environmentally friendly products and processes will be economical in the long term as they circumvent the need for treating 'end-of-the-pipe' pollutants and by-products generated by conventional synthesis. The fundamentals and significant outcomes of microwave-assisted organic synthesis in aqueous medium are summarized in this tutorial review, which have resulted in the development of relatively sustainable and environmentally benign protocols for the synthesis of drugs and fine chemicals.

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Microwave-assisted cyclocondensation of hydrazine derivatives with alkyl dihalides or ditosylates in aqueous media: syntheses of pyrazole, pyrazolidine and phthalazine derivatives

Cited by 71 publications

References 30 publications

“Greener” chemical syntheses using mechanochemical mixing or microwave and ultrasound irradiation

“Greener” chemical syntheses using mechanochemical mixing or microwave and ultrasound irradiation

Michael Cyclization of Polarized Systems: Synthesis and in vitro Anti-Diabetic Evaluation of Some Novel Pyrimidine, Pyridine, Pyrazole and Pyrazolo[3,4-b ]pyridine Derivatives

Aqueous microwave chemistry: a clean and green synthetic tool for rapid drug discovery

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