A facile and efficient ultrasound-assisted synthesis of novel dispiroheterocycles through 1,3-dipolar cycloaddition reactions

A Green one-pot three component synthesis of thiazolidine-2,4-dione based bisspirooxindolo-pyrrolidines with [Bmim]BF4: their in vitro and in silico anti-TB studies

A simple and effective three-component one-pot green methodology was employed for the synthesis of a new thiazolidine-2,4-dione based bisspirooxindolo-pyrrolidine derivatives using [Bmim]BF4 ionic liquid via [3 + 2] cycloaddition reaction. It is an environmentally benign, column chromatography-free, shorter reaction time, good yield and easy product isolation method. The synthesized compounds 10a-x, were thoroughly characterized by using various spectroscopic methods like FT-IR, 1H NMR, 13C NMR, Mass spectrometry and finally by single crystal X-ray diffraction method. In vitro anti-tubercular (anti-TB) activity studies were carried out on these synthesized compounds, and they showed good to moderate anti-TB activity against Mycobacterium tuberculosis H37Rv strain. The compound 10a exhibited good anti-TB activity, with an MIC (Minimum Inhibitory Concentration) value of 12.5 µg/mL, and the compounds 10m, 10o and 10r showed moderate activity with an MIC value of 25.0 µg/mL. Remaining compounds exhibited poor activity against Mycobacterium tuberculosis. Ethambutol, rifampicin and isoniazid were used as standard drugs. Furthermore, in silico molecular docking experiments on the TB protein (PDB ID: 1DF7) were carried out to understand the binding interactions, and they showed least binding energy values ranging from -8.9 to -7.2 kcal/mol.

Ultrasonic irradiation-assisted MnFe2O4 nanoparticles catalyzed solvent-free selective oxidation of benzyl alcohol to benzaldehyde at room temperature

Magnetic nanoparticles (NPs) play a vital role in heterogeneous catalysis because of their easy separation, and effective recyclability. Herein, we report the synthesis of MnFe2O4 NPs for use as catalysts in the selective oxidation of benzyl alcohol to benzaldehyde under mild conditions. The MnFe2O4 NPs have been synthesized by precipitation method followed by hydrothermal ageing at 180 °C for 4.0 h. We have investigated the effect of chitosan and carboxymethyl cellulose on the size or morphology of the formed MnFe2O4 NPs. The X-ray diffraction study confirms the formation of pure and crystalline MnFe2O4 with varying average crystallite sizes ranging from 18 to 28 nm based on the type of additive used. The electron microscopy study reveals that the additive plays a significant role in controlling the morphology of the formed MnFe2O4 NPs. These MnFe2O4 NPs exhibit superparamagnetic behaviour at room temperature and can effectively catalyze the solvent-free selective oxidation of benzyl alcohol to benzaldehyde in the presence of tert-butyl hydroperoxide at room temperature under ultrasonic irradiation. The developed protocol can be extended to various substituted benzyl alcohols having both the electron withdrawing and electron donating groups to afford moderate to excellent yield of the products. The catalyst is magnetically retrievable, highly stable, and can be reused up to the sixth run without significant loss of catalytic activity.

Ultrasonic Preparation and Reactivity of 4,5-dihydro-1H-pyrazole Derivatives

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The regiospecific synthesis of 1H-pyrazole derivatives has been accomplished through the 1,3-dipolar cycloaddition of aryldiazoalkane to but-3-en-2-one. A convenient and inexpensive ultrasound-assisted preparation of cyclopropenes in good yields has been realized. The effect of solvent, ultrasonic power, frequency, reaction time and temperature of cyclopropenation were studied and the order of yield indicates Ultrasound, 25 KHz > Ultrasound, 40 KHz > conventional synthesis method.

Sonochemical Protocols for Heterocyclic Synthesis: A Representative Review

In the present era of the industrial revolution, we all are familiar with ever-increasing environmental pollution released from various chemical processes. Chemical production has had a severe impact on the environment and human health. For the betterment of our environment, the chemical community has turned their interest to developing green, harmless and sustainable synthetic processes. To accomplish these goals of green chemistry, the extraordinary properties of sonication play an important role. It is well known that sonochemistry can make decisive contributions to creating high pressures of almost 1000 atm and very high temperatures in the range of 4500-5000 °C. The implementation of ultrasound in chemical transformations somehow fulfils the measures of green chemistry, as it reduces energy consumption, enhances product selectivity, and uses lesser amounts of hazardous chemicals and solvents. Furthermore, heterocyclic synthesis under ultrasonication offers several environmental and process-related advantages compared with conventional methods. The remarkable contribution of ultrasonics to the development of green and sustainable synthetic routes inspired us to write this article. Herein, we have discussed only some of the various synthetic methodologies developed for the construction of heterocyclic cores under ultrasonic irradiation, accompanied by mechanistic insights. In some cases, a comparison between sonochemical conditions and conventional conditions has also been investigated. We emphasized principally 'up to date' developments on various sono-accelerated chemical transformations comprising aza-Michael, aldol reactions, C-C couplings, oxidation, cycloadditions, multi-component reactions, etc. for the synthesis of heterocycles.

Antimicrobial Activity and In Silico Molecular Docking Studies of Pentacyclic Spiro[oxindole-2,3′-pyrrolidines] Tethered with Succinimide Scaffolds

Three-component cascade reactions of (E)-3-arylidene-1-methyl-pyrrolidine-2,5-diones, L-valine and various isatin derivatives are described. A series of 17 spiropyrrolidine derivatives with wide structural complexity and diversity have been thus obtained in moderate to excellent yields under mild reaction conditions. The structure and stereochemistry of these N-heterocyclic cycloadducts has been established by spectroscopic techniques and unambiguously confirmed by a single-crystal X-ray diffraction analysis performed on one derivative. UV-visible spectra have been recorded for all new compounds. Furthermore, the synthesized N-heterocyclic compounds have been screened for their in vitro antibacterial and antifungal activities. Several derivatives exhibited moderate to good activities, comparable to those of the known standard drugs Amphotericin B and Tetracycline. Structural activity relationships (SARs) and molecular docking of the most promising derivatives into the binding sites of glucosamine 6-phosphate synthase (GlcN6P) and methionyl-trna-synthetase (1PFV) were also established. Furthermore, pharmacokinetic studies indicate that the heterocycles exhibit acceptable predictive ADMET (absorption, distribution, metabolism, excretion, and toxicity) properties and good drug ability.

2-Azaallyl Anions, 2-Azaallyl Cations, 2-Azaallyl Radicals, and Azomethine Ylides

This review covers the use of 2-azaallyl anions, 2-azaallyl cations, and 2-azaallyl radicals in organic synthesis up through June 2018. Particular attention is paid to both foundational studies and recent advances over the past decade involving semistabilized and nonstabilized 2-azaallyl anions as key intermediates in various carbon-carbon and carbon-heteroatom bond-forming processes. Both transition-metal-catalyzed and transition-metal-free transformations are covered. Azomethine ylides, which have received significant attention elsewhere, are discussed briefly with the primary focus on critical comparisons with 2-azaallyl anions in regard to generation and use.

Ultrasound-assisted one-pot multicomponent 1,3-dipolar cycloaddition strategy: combinatorial synthesis of spiro-acenaphthylene-S,S-acetal and 2H-pyranone derivatives

The stereo/regio/chemoselective syntheses of a library of novel spiro[acenaphthylene-1,3′-pyrrolizin]-2-one and spiro[acenaphthylene-1,5′-pyrrolo[1,2-c]thiazol]-2-one have been achieved through 1,3-dipolar cycloaddition.

Catalyst-free, one-pot, four-component green synthesis of functionalized 1-(2-fluorophenyl)-1,4-dihydropyridines under ultrasound irradiation

A catalyst-free synthesis protocol for functionalized 1,4-dihydropyridines under ultrasonic irradiation in aqueous ethanol is reported with excellent yields. Eleven new compounds are synthesized using dimethylacetylenedicarboxylate, 2-fluoroaniline, malononitrile and various substituted aldehydes.

Ultrasonic-accelerated rapid protocol for the improved synthesis of pyrazoles

A simple, catalyst-free, green synthetic protocol is described for the one-pot synthesis of pyrazoles via multicomponent reaction of aromatic aldehydes, hydrazine monohydrate and ethyl acetoacetate and malononitrile/ammonium acetate in water under ultrasound irradiation. This protocol avoids traditional chromatography and purification steps and it affords highly selective conversion with no byproducts.

Molecular diversity of spirooxindoles. Synthesis and biological activity

Spirooxindoles are important synthetic targets possessing extended biological activity and drug discovery applications. This review focuses on the various strategies for the enantioselective synthesis of spirocyclic oxindoles relying on reports over the past decade and from earlier work. The spirooxindoles in this review are separated into three structural classes, and then further categorized into the method type from which the spirocycle is generated.

Highly diastereoselective synthesis of imidazolidine-dispirooxindoles via three-component [3 + 2] cycloadditions of isatins, 2-(aminomethyl)pyridine and isatin-based imines

In the presence of Et₃N, the [3 + 2] cycloaddition of isatins, 2-(aminomethyl)pyridine and isatin-based imines proceeded readily, and furnished novel imidazolidine-dispirooxindoles in up to 84% yield with up to >99 : 1 diastereoselectivity.

One-pot three-component synthesis of 3-hydroxy-5,5-dimethyl-2-[phenyl(phenylthio)methyl]cyclohex-2-enone derivatives under ultrasound

3-Hydroxy-5,5-dimethyl-2-[phenyl(phenylthio)methyl]cyclohex-2-enone is synthesized via one-pot three-component reactions of aromatic aldehyde, substituted thiophenol and 5,5-dimethyl-1,3-cyclohexanedione catalyzed by p-dodecylbenzene sulfonic acid (DBSA) under ultrasound. Under ultrasound irradiation the yields are much higher (sometimes substantially, by almost double) and the reaction time decreases substantially, the reaction conditions are milder. This method provides several advantages such as environment friendliness, high yields and simple work-up procedure and the protocol provides a novel alternative for the synthesis of thioether.

A strategic approach to the synthesis of functionalized spirooxindole pyrrolidine derivatives: in vitro antibacterial, antifungal, antimalarial and antitubercular studies

A series of spirooxindole pyrrolidine derivatives has been synthesized and evaluated for theirin vitrobiological activities. The observed regio- and stereoselectivity of the cycloaddition reaction has been rationalized using DFT calculations.

Ultrasound-assisted sequential multicomponent strategy for the combinatorial synthesis of novel coumarin hybrids

The present investigation reports an easy access to a library of novel spiro-oxindole-pyrrolizine or pyrrolo[1,2-c]thiazole fused coumarin hybrid heterocycles through a one-pot sequential four-component reactions of 2,2-dimethyl-1,3-dioxane-4,6-dione, salicylaldehydes, isatins, and cyclic α-amino acids under ultrasound irradiation.

Efficient and regioselective synthesis of novel functionalized dispiropyrrolidines and their cytotoxic activities

An efficient and regioselective synthesis of novel functionalized dispiropyrrolizidine derivatives via a three-component [3 + 2] cycloaddition reaction of azomethine ylides is described. This protocol has the advantages of high efficiency, mild reaction conditions, a one-pot procedure, and convenient operation. Many of these compounds were evaluated for their antiproliferative properties in vitro against cancer cells and several compounds were found to have good activities.

Ultrasound-promoted one-pot, four-component synthesis of pyridin-2(1H)-one derivatives

An efficient one-pot synthesis of 1,6-diamino-2-oxo-1,2,3,4-tetrahydro- pyridine-3,5-dicarbonitrile derivatives by four-component piperidine-catalyzed reactions of a ketone, malononitrile, ethyl cyanoacetate and hydrazine hydrate under ultrasound irradiation is described. This method provides several advantages such as shorter reaction times, excellent yields, and a simple workup procedure.

Green synthesis and biological evaluation of new di-α-aminophosphonate derivatives as cytotoxic agents

A series of novel di-α-aminophosphonate derivatives were synthesized by a one-pot method in the presence of PEG-H2 O under ultrasonic irradiation and were characterized by IR, (1) H NMR, (13) C NMR, mass spectrometry, and elemental analysis. The newly synthesized compounds were evaluated for their cytotoxic activities against the human lung cancer cell line H1299 and the human breast cancer cell line MCF7 in vitro by the MTT method. All compounds showed moderate cytotoxic activity on both cell lines, and compounds 4b and 4c showed marked activity.

A facile synthesis of functionalized dispirooxindole derivatives via a three-component 1,3-dipolar cycloaddition reaction

An efficient synthesis of novel dispirooxindoles has been achieved through three-component 1,3-dipolar cycloaddition of azomethine ylides generated in situ by the decarboxylative condensation of isatin and an α-amino acid with the dipolarophile 5-benzylideneimidazolidine-2,4-dione. The improved procedure features mild reaction conditions, high yields, high diastereoselectivities, a one-pot procedure and operational simplicity.

Synthesis of novel 16-spiro steroids: spiro-7'-(aryl)tetrahydro-1H-pyrrolo[1,2-c][1,3]thiazolo-trans-androsterone hybrid heterocycles

The 1,3-dipolar cycloaddition of azomethine ylide derived in situ from the reaction of acenaphthylene-1,2-dione and 1,3-thiazolane-4-carboxylic acid to various exocyclic dipolarophiles synthesized from trans-androsterone and trans-dehydroandrosterone afforded a library of novel spiro[5'.2″]acenaphthylene-1″-one-spiro[16.6']-(7'-aryl)-tetrahydro-1H-pyrrolo [1,2-c][1,3]thiazolo-trans-androsterone/dehydroandrosterone hybrid heterocycles respectively. These reactions proceeded stereo-specifically affording a single isomer of the 16-spiro steroids in excellent yields.

An efficient synthesis of novel dispirooxindole derivatives via one-pot three-component 1,3-dipolar cycloaddition reactions

A series of novel dispirooxindoles have been synthesized through three-component 1,3-dipolar cycloaddition of azomethine ylides generated in situ by the decarboxylative condensation of isatin and an α-amino acid with the dipolarophile 5-benzylidene-1,3-dimethylpyrimidine-2,4,6-trione. This method has the advantages of mild reaction conditions, high atom economy, excellent yields, and high regio- and stereo-selectivity.