Ultrasound-assisted multicomponent synthesis of heterocycles in water – A review

Ramakanth Pagadala; Venkatesan Kasi; Nhlanhla Gracious Shabalala; Sreekantha B. Jonnalagadda

doi:10.1016/j.arabjc.2021.103544

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Review article

01 2021

:15;

103544

doi:

10.1016/j.arabjc.2021.103544

Ultrasound-assisted multicomponent synthesis of heterocycles in water – A review

Ramakanth Pagadala^{^a,^b}, Venkatesan Kasi^{^a}, Nhlanhla Gracious Shabalala^{^b}, Sreekantha B. Jonnalagadda^{^b,⁎}

a Chemistry Division, H&S Department, CVR College of Engineering, Hyderabad, India

b School of Chemistry and Physics, University of KwaZulu-Natal, Westville Campus, Chiltern Hills, Durban 4000, South Africa

⁎Corresponding author. Jonnalagaddas@ukzn.ac.za (Sreekantha B. Jonnalagadda)

Received: 2021-9-6, Accepted: 2021-11-2,

Disclaimer:
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.

Peer review under responsibility of King Saud University.

Abstract

Abstract

Ultrasound-assisted multicomponent reactions in water are great implements for the development of bioactive compounds. The methodologies for the synthesis of different heterocyclic molecules have acquired enormous attention. Many such techniques are energy-intensive and associated with hazardous chemicals, solvents, expensive work-ups. Low yields and multi-step schemes generate huge organic waste. Hence, researchers thus focussed on benign and eco-friendly techniques to assemble heterocyclic analogs and drug molecules. The ultrasound-assisted synthesis of the target organic moieties frequently facilitates higher product yields than other methodologies. This review is focused on ultrasound-aided multicomponent reactions for synthesizing varied nitrogen-, oxygen-, and sulfur-containing heterocyclic compounds using water as the solvent. The advantages and limitations with respect to yields and reaction conditions are discussed. This evaluation covered the literature reports from 2014 to date.

Keywords

Water as a solvent

Ultrasonic irradiation

One-Pot

Multicomponent reaction

N-, O-, and S-Heterocycles

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1 Introduction

The effect of ultrasound on chemical reaction rates has received significant interest in recent years as ultrasonic irradiation enhances the rate of numerous chemical reactions, such as polymerization, oxidation, and reduction processes (Weissler, 1953). The chemical reactions continue via the creation and adiabatic disintegration of transitory cavitation bubbles. In such systems, the ultrasound will increase the mechanical agitation and mixing, rise in reaction pressure and temperature, and hydrogen ion concentration via sonic ionization of water because of cavitation. Furthermore, sonochemical protocol tested to be a possible alternative energy source for the construction of chemical compounds.

Using ultrasound technology to modify chemical reactions has intensely increased, in particular organic synthesis. In the liquid phase, ultrasonic waves cause cavitation, including bubble nucleation, growth, and collapse. Bubble collapsing occurs at millions of locations across the liquid medium, resulting in supercritical conditions such as high temperature (5000 K) and high pressure (1000 atm) (Tizhoosh et al., 2020; Rad et al., 2021; Oskouia et al., 2019 ). Cavitation considerably increases the local temperature and pressure inside the cavitation bubbles, providing energy for chemical stimulation and improving mass transfer when the bubbles collapse (Mason and Lorimer, 2002; Cella and Stefani, 2009). Cavitation produces reaction intermediates inclusive of radical-ions, which accelerate the chemical reaction. Possibly, the cavitation for nuclei takes place quicker in water rather than in other solvents. Water additionally transfers ultrasonic energy more efficiently than other solvents. As a result, with an increase in ultrasound power, much energy is furnished to the reaction mixture to boost the cavitation effect. When the ultrasonic intensity surpasses an appropriate amount, many gas bubbles form in the reaction vessel because of the scattering of gas bubbles on sound waves. In 2017, Banerjee et al. (Banerjee, 2017) published a review on “Recent developments on ultrasound-assisted catalyst-free organic synthesis.” This review summarises the ultrasound impact on organic synthetic reactions and the trendy developments on ultrasound-assisted catalyst-free conditions.

Green chemistry is a rapidly growing area that provides a promising path for eco-friendly and sustainable science and technology (Li, 2005; Potewar et al., 2008). Green chemistry offers effectual and benign synthetic methodologies for the improvement of life-saving drugs. Furthermore, water gives many practical advantages as a solvent, including cost-effectiveness, safety, elimination of volatile organic solvents, and eco-compatibility (Doustkhah et al., 2016; Panahi et al., 2019). In addition, water can accelerate the reaction rate and selectivity of numerous chemical reactions through hydrophobic effects because of its unique chemical and physical properties. On the other hand, multicomponent reactions (MCRs) have acquired substantial attention because of their efficiency, high selectivity, atom economy, one-pot, decreased number of steps in product formation, and operational simplicity (Varma, 1999; Tietze, 1996; Dömling, 2006 ). Notably, MCR has become an attractive approach that plays a vital role in modern synthetic chemistry. These reactions help generate libraries of drug-like molecules, which may simplify the optimization of the drug development processes (Weber, 2002; Hulme and Gore, 2003). More than 50% of the life-saving drugs consist of heterocyclic structures (Brahmachari, 2010; Brahmachari and Approaches, 2014). Nitrogen and oxygen-containing heterocyclic scaffolds are the main constituents of many conventional medicines with vast antimicrobial activity (Kumar et al., 2009; Morgan et al., 2002; Rueping et al., 2008; Raj et al., 2010 ).

Numerous benefits associated with ultrasound attracted organic chemists to investigate its scope to a greater depth. As a result, several ultrasound-assisted processes to synthesize different bioactive heterocycles have been developed. Some reviews covering various aspects of multicomponent reactions using ultrasonication have been reported (Banerjee, 2017; Banerjee, 2017; Banerjee, 2017; Navjeet, 2018; Navjeet, 2018; Kaur et al., 2018; Banerjee, 2019; Ujwaldev et al., 2019; Ziarani et al., 2020; Saranya et al., 2021 ). As a part of our continuing pursuit, the current inclusive study describes the latest advances with ultrasound utilization combined with the MCRs with water as the medium to generate diverse biologically active nitrogen, oxygen, and sulfur, containing heterocyclic compounds.

2 Preparation of N-heterocyclic compounds in water:

One-pot synthesis of heterocyclic analogs under aqueous conditions has become an attractive alternative in modern organic chemistry. This section discusses the latest developments in ultrasound irradiated MCRs for N-heterocyclic derivatives under eco-friendly conditions.

2.1

2.1 Pyridines and Pyrimidines:

Pyridines and their derivatives have fascinated researchers, and their features led to the discovery of many commendable bio-active agents (Cocco et al., 2007; May et al., 2007; Guo et al., 2008 ). Pyridines are recognized as potent inhibitors of HIV-1 integrase (Deng et al., 2007), IKK-β inhibitors (Murata et al., 2003), and A_2A adenosine receptor antagonists (Mantri et al., 2008). The pyrimidine heterocyclic core possesses many microbial properties, such as antihypertensive, vasodilators, antiallergic, cardiac stimulant, antirubella, anticancer activities (Koroleva et al., 2010; Figueroa-Villar et al., 1992; Rosowsky et al., 2004; Rosowsky et al., 1973; Jain et al., 2006 ). Because of their broader scope in the pharmaceutical arena, techniques for synthesizing new pyridine and pyrimidine derivatives received enormous attention. Although several routes have been reported (Heravi et al., 2009; Evdokimov et al., 2006; Zou et al., 2011; Ren et al., 2011; Mobinikhaledi et al., 2004; Akbari et al., 2008; Khan et al., 2012 ); many of those approaches suffer various disadvantages, such as harsh reaction conditions and low yields. Pagadala et al. (Pagadala et al., 2014) established an ultrasound-supported expeditious and straightforward protocol for the one-pot generation of pyridines (Scheme 1) and pyrimidines (Scheme 2) at room temperature with excellent yields (94–98%) and (88–95%), respectively.

Ali et al. (Maleki and Aghaei, 2017) developed an ultrasound boosted one-pot approach for tetraheterocyclic imidazo(thiazolo)pyrimidines (Scheme 3) using Fe₃O₄@clay as a catalyst. For the first time, the authors introduced Fe₃O₄@clay based catalyst to prepare ten derivatives of imidazopyrimidines under ultrasonic conditions. At hand precursors, easy work-up conditions, reusability of the catalyst, short 10–15 min of the reaction at room temperature, excellent 90–98% product yield, and evading of hazardous organic solvents are the main advantages of this protocol. The same group suggested fifteen pyrimidine-6-carboxylic esters under similar conditions through a four-component reaction among 2-cyano-guanidine, sodium azide, different substituted aromatic aldehydes, and methyl/ethyl acetoacetate. Using Fe₂O₃@SiO₂-(CH₂)₃NHC(O)(CH₂)₂PPh₂ as a nanomagnetic catalyst reaction gave 80–90% yields (Scheme 4) (Maleki et al., 2018).

Preparation of imidazo(thiazolo)pyrimidines.

Preparation of tetrazolo[1,5-a]pyrimidines using a nanomagnetic catalyst.

Duygu et al. (Bayramoğlu et al., 2020) reported a relatively efficient ultrasound facilitated procedure for the construction of six different 2-aminopyrimidine derivatives via reacting different substituted β-diketones and guanidine hydrochloride in good yields (72–80%) at 60 °C (Scheme 5). The authors also have compared the reaction performance under reflux and ultrasonic methods. Compared to conventional reflux methods with longer reaction times (1 h to overnight), the ultrasonic approach lowered the reaction time to 30 min.

Preparation of 2-aminopyrimidine derivatives.

Kumar et al. reported an environmentally benign sonochemical method (Godugu et al., 2020). Natural dolomitic limestone as a reusable catalyst to generate seventeen dihydropyrimidinones (Scheme 6) and eighteen fully substituted pyridine derivatives (Scheme 7) using EtOH-water mixture with 90–98 % yields. The authors received the pure products without chromatographic purification, and the catalyst was recycled seven times with no loss of catalytic activity. A series of fused pyrazolopyranopyrimidines (Scheme 8) were synthesized by Satish et al. (Akolkar et al., 2020) under ultrasound irradiation. The four-component reaction involved the fusion of barbituric acid, ethyl acetoacetate, and hydrazine hydrate with different aromatic aldehydes, in water using β-Cyclodextrin as a biomimetic catalyst. They constructed 21 different fused tri-heterocyclic pyrazolopyranopyrimidines using various aldehydes with 84–93% yields at 50 °C.

Preparation of dihydropyrimidinone/-thiones.

Preparation of pyrazolopyranopyrimidines.

Hossein et al. (Naeimi and Didar, 2017) described a modest and cost-effective one-pot protocol for the generation of pyrido[2,3-d:6,5-d]dipyrimidines (Scheme 9) from the reaction of various aldehydes, ammonium acetate, and 2-thiobarbituric acid using copper ferrite nanoparticles as a reusable heterogeneous catalyst under ultrasound irradiation in aqueous media at 80 °C. The authors synthesized ten pyrido[2,3-d:6,5-d]dipyrimidine derivatives using different aromatic aldehydes with excellent yields (90–99%). Furthermore, the authors reported superb results with reduced reaction times under ultrasonication compared to the reflux method.

Verma et al. (Verma et al., 2020) developed a new one-pot three-component method for constructing 21 bioactive imidazopyrimidine compounds (Scheme 10) by reacting different substituted aromatic aldehydes, 2-aminobenzimidazole, and active methylene molecules with starch functionalized Fe₃O₄ nanoparticles as a heterogeneous catalyst under ultrasound irradiation in water at room temperature. Primarily, the authors observed 80% yield in 2 h at reflux condition. The same reaction yielded 98% of the targeted compound in 3 min under ultrasonic irradiation. The authors assessed the efficacy of toluene, xylene, benzene, 1,4-dioxane, acetonitrile, dichloromethane, ethanol and methanol as solvents. Water offered superior results. Under ultrasonic irradiation, the pyridine and pyrimidine derivatives were produced two to four times faster with higher yields than conventional conditions.

Interestingly, the spatial hindered aromatic aldehydes also gave good results, stressing that the ultrasound approach is ideal for assembling pyridine and pyrimidine derivatives.

2.2

2.2 Pyrazoles

Pyrazoles are common and vital motifs in numerous biologically active heterocyclic compounds (Milano et al., 2008; Souza et al., 2002; Bailey et al., 1985; Prakash et al., 2009; Abdel-Aziz et al., 2009; Lange and Kruse, 2005 ). Commercialized drugs like Viagra, Acomplia, and Celebrex embody the pyrazole framework (Penning et al., 1997; Terrett et al., 1996). The potential applications motivated the research scientists to search for innovative routes for new pyrazole-containing molecules. Many such protocols suffer some drawbacks, including low yields, complicated procedures and the need for toxic solvents and catalysts. Thus, one of the significant successes is the use of ultrasound in chemical processes.

Shabalala et al. (Shabalala et al., 2015) developed a modest technique for the one-pot synthesis of nine pyrazoles and eight pyranopyrazoles in aqueous media under ultrasonic irradiation with 90–97% yield (Scheme 11). Ultrasound irradiation pertains to the traditional approach, requiring much less time for assembling the pyrazolopyridines (1.5 h to 2.5 h) and pyranopyrazole derivatives (0.5 h to 1.5 h) at lower temperatures (50 °C) than the traditional heating (70 °C). This approach provided better yields of pure products without chromatographic purification.

Wang et al., (Liju et al., 2015) synthesized eighteen spiro[indoline-3,4-pyrano [2, 3-c]pyrazole] compounds at room temperature under ultrasound using L-proline with 1:1 v/v ethanol/water with 84–93% yields (Scheme 12). Manisha et al. (Mishra et al., 2020) have developed an expeditious route and synthesized fourteen novel pyrano[2,3-c]pyrazoles (Scheme 13) and four bis-pyrano[2,3-c]pyrazoles (Scheme 14) in water using 18-Crown-(Cella and Stefani, 2009)-ether as a catalyst.

Preparation of spiro[indoline-3,4′-pyrano[2,3–c]pyrazole] derivatives.

Water is proved the best medium among methanol, acetonitrile, DMSO, DMF, toluene, dichloromethane, and water. Under reflux, the product formation took 40 min with a 50% yield. However, under ultrasound irradiation, within 10 min, 92% yield is obtained. Maddila et al. (Maddila et al., 2019) used Mn-doped zirconia as a successful catalyst for assembling fourteen pyrano[2,3-c]pyrazoles (Scheme 15) with 88–98% yield under ultrasound with 1:1 v/v ethanol/water at room temperature. Smita et al. (Khare et al., 2019) generated ten 1,2,3-triazolyl pyrano[2,3-c]pyrazole derivatives (Scheme 16) with 92–98% yield at 30 °C in water with NaHCO₃ as a catalyst, by sonochemical method. Dandia et al. (Dandia et al., 2014) described an eco-friendly approach for the construction of twelve different pyrazolo[3,4-b]pyridine derivatives (Scheme 17) with 84–95% yield in water through a three-component fusion of various substituted aldehydes, 3-amino-5-methylpyrazole and ethyl cyanoacetate using NaCl as a catalyst at room temperature.

Preparation of pyrano[2,3–c]pyrazoles-3-carboxylate.

Preparation of 1,2,3-triazolyl pyrano pyrazole.

Although the various methodologies for synthesizing different pyrazole compounds, the ultrasound method establishes a favorable environment in water medium within less reaction time, offering superior yields with electron-withdrawing and donating substitutes on aldehydes

2.3

2.3 Quinolines and their derivatives

Quinolines are the principal family of N-heterocyclic compounds. Many antidiabetic, antihypertension, anticancer, antimalarial, and other drugs constitute the quinolone skeleton (Bandgar et al., 2008; Kumar et al., 2008; Hong et al., 2010; Beagley et al., 2003; Sawada et al., 2004; Ma et al., 2004; Denton et al., 2005; Fokialakis et al., 2002; Fossa et al., 2002; Ryckebusch et al., 2003 ). Due to the high demand for quinoline derivatives, many synthetic methods have been developed. Amongst them, the ultrasonic aided MCRs are relatively more attractive to obtain this target molecule. The hierarchy of green and efficient techniques for designing ultrasonic multicomponent reactions, water is the most desired solvent with essential environmental and commercial benefits. Pagadala et al. (Pagadala et al., 2014) synthesized nine valuable dihydroquinoline derivatives under an ultrasonic condition in water with excellent yields of 90–97% (Scheme 18). The authors synthesized the dihydroquinolines under conventional heating and ultrasound conditions. The traditional reactions at 60 °C completed in 3.0 h to 4.5 h with 70 to 82% yield. Under ultrasound irradiation, comparatively within a short time, i.e., 1.0 h to 1.5 h, obtained 90 to 97% yield. Prasad et al. (Prasad et al., 2018) explored SnCl₂·2H₂O as a catalyst for the one-pot preparation of sixteen 2-substituted quinolones by a three-component fusion in water at 60 °C under ultrasound condition (Scheme 19). The reaction of ethyl 3,3-diethoxypropionate with different anilines and aldehydes, proceeded through Sn(IV) species generation, provided broader substrate scope and good yields (64–80%). Many of the compounds showed encouraging activities against gram-positive and gram-negative species. Diksha et al. (Bhardwaj et al., 2019) reported the efficiency of the TiO₂ nanocatalyst for the synthesis of twelve 8-aryl-7,8-dihydro-(Weissler, 1953; Rad et al., 2021)-dioxolo[4,5-g]quinolin-6(5H)-one derivative (Scheme 20) after exploring the reaction under various conditions. The MCR of various aromatic aldehydes, 3,4-methylenedioxy aniline, and Meldrum's acid used ultrasound in water media provided 85–91% yield.

Sn-catalyzed synthesis of 2-substituted quinolines.

Preparation of 8-aryl-7,8-dihydro-[1,3]-dioxolo[4,5–g]quinolin-6(5H)-ones.

2.4

2.4 Benzodiazepines

Benzodiazepines are a significant class of biologically active nitrogen compounds with broadly recommended psychotropic groups and well-studied pharmacophoric frameworks. Benzodiazepines are critical structural components of many sedatives, HIV-1 protease inhibitors, muscle relaxants, insecticides, anxiolytics, hypnotics, antihistamines, and anti-ulcerative, anti-inflammatory, and anticoagulant molecules (Al-Muhaimeed, 1997; Scott et al., 2002; Nakano et al., 2000; Kumar et al., 2006; Fader et al., 2011; Foden et al., 1975 ). Due to their prominence, many synthetic routes for benzodiazepines Suresh et al. (Maury et al., 2021) reported an ultrasound-mediated protocol synthesizing seventeen novel 1,4-benzodiazepine scaffolds (Scheme 21) with 85–95% yield through a three-component reaction of isatin, 1, 2-phenylenediamine, and 5,5-dimethylcyclohexane-1,3-dione at 80 °C. Water proved the perfect solvent compared with methanol, ethanol, n-hexane, xylene, and CCl₄. Among the catalysts, acetic acid, p-TSA, TFA, ZnCl₂, HCl, Fe₂O₃, TiO₂, AlCl₃, NH₂SO₃H examined, none improved the product yield. The data displays a catalytic function of water in the reaction.

2.5

2.5 1,8-Dioxodecahydroacridines

1,4-dihydropyridines are effective in treating cardiovascular problems and congestive heart failure (Janis et al., 1987). Acridine-1,8-diones are structurally associated with 1,4-dihydropyridines. The molecules are also employed in laser dyes with high-lasing efficacies (Vo et al., 1995) and photoinitiators (Murugan et al., 1998). In addition, acridine-1,8-diones have a broad spectrum of pharmacological actions like anticancer (Reinert et al., 2003), antimalarial (Gamage et al., 1999), antitumor (Spalding et al., 1954), fungicidal (Mikata et al., 1998), anticarcinogenic (Wainwright, 2001). The demand of acridine‐1,8‐dione, Asha et al. (Chate et al., 2016) reported an ecofriendly method using biodegradable β‐cyclodextrin as a reusable catalyst. Under ultrasonication in water, twenty 1,8-dioxodecahydroacridines were synthesized with medium to excellent yields (56–94%) (Scheme 22). The three-component reactions involved dimedone, benzaldehydes, and anilines. Among different solvents (acetonitrile, DMF, tetrahydrofuran, water, ethanol, and aqueous ethanol) water proved the most effective solvent.

Ultrasound promoted Preparation of N‐substituted 1,8‐dioxo‐decahydroacridines.

2.6

2.6 Pyrroles

Pyrroles are the nitrogen-containing heterocycles and components of important natural bioactive compounds. Pyrroles contain the essential features for pharmacological and material science applications (Novák et al., 1997; Trofimov et al., 2004; Higgins, 1997; Bellina and Rossi, 2006; Lee et al., 2000; Boger et al., 1999; Domingo et al., 2001; Pu et al., 2007; Gholap, 2016; Joshi et al., 2016; Fan et al., 2008 ). Many synthetic protocols for constructing pyrroles were reported (Kamijo et al., 2005; Martín et al., 2006; Beck et al., 2006; Hwang et al., 2008; Brichacek and Njardarson, 2009; Zhu et al., 2009; Fu et al., 2009; Fujiwara et al., 2009; Attanasi et al., 2011; Palmieri et al., 2011; Liu et al., 2010; Yan et al., 2010; Wang et al., 2013 ); however, eco-friendly techniques remain an attractive objective. In 2017, Pagadala et al. (Pagadala and Anugu, 2018) had designed an efficient four-component one-step fusion generating twelve novel substituted pyrroles using water as a solvent (Scheme 23). The ultrasound promoted method offered 88–93% yields. The conventional way provided relatively poor results.

3 Preparation of oxygen-containing heterocycles in water:

Under ultrasound irradiation conditions, water as the optimum solvent developed more prevalent for synthesizing different oxygen-containing heterocycles.

3.1

3.1 Pyrans

Pyran is a six-membered nonaromatic ring containing five carbon atoms, one oxygen atom, and two double bonds. Those are the building blocks and central part of many natural and synthetic molecules which display different pharmacological characteristics. 4H-pyrans in particular, exhibit many antifungal, antimicrobial, anticancer, spasmolytic, anti-anaphylactic, and anti-inflammatory properties (Green et al., 1995; Reddy et al., 2017; de Souza et al., 2004; Udhaya Kumar et al., 2019; Aytemir et al., 2004; Banerjee et al., 2011 ). Many naturally occurring products and medicinal compounds have the 4H-pyran core (Pratap and Ram, 2014; Sonsona et al., 2015). In addition, the cosmetic and agricultural industries also make use of this family of organic molecules (Schweizer, 1977). The importance of pyrans and their derivatives prompted many new protocols for those moieties with growing interest. Most researchers reported methods exploring different catalysts, reagents, and solvents (Kumar et al., 2009; Bhattacharyya et al., 2012; Seshu Babu et al., 2008; Balalaie et al., 2006; Peng and Song, 2007; Heravi et al., 2009; Martin et al., 1988; Heber and Stoyanov, 2003; Jin et al., 2004; Jin et al., 2004; Pratap et al., 2011 ). Although these procedures have merits, many of the processes suffer from drawbacks, such as harsh reaction environments, work-up methods, lengthy reaction times, and low yields.

Generally, utilizing water as solvent or co-solvent is a challenging task in organic synthesis, although it is the most eco-friendly medium (Jessop, 2011; Pagadala et al., 2015; Pagadala et al., 2015; Pagadala et al., 2014 ). The advantages of water as a solvent many and abide by the principles of Green Chemistry (Tundo et al., 2000; Constable et al., 2007; Sheldon, 2012 ). Thus, an attractive preference is continually engaging water as a solvent in organic synthesis. In this context, sonication of MCRs in an aqueous medium speeds up the reaction through improved interaction. Several researchers explored the benefits of ultrasound-assisted synthesis. Binoyargha et al. (Dam et al., 2015) introduced nano-Fe₃O₄-DOPA-L-proline catalyst to prepare twelve different substituted pyrans via four-component fusion of different substituted aldehydes, ethyl acetoacetate, hydrazine hydrate, malononitrile in water under ultrasound at room temperature (Scheme 24). Among the catalysts examined, the nano-Fe₃O₄-DOPA-L-proline has proven best. The ultrasound approach produced improved yields (89–98%) in a shorter time at room temperature relative to the reflux method.

Preparation of pyrano-pyrazolone derivatives.

Gohil et al. (Gohil et al., 2016) reported an efficient protocol for the synthesis of eight different pyrano [3,2-c]chromenes and eight benzo pyrano [4,3-b] chromene derivatives. The reactions involved 4-hydroxy coumarin, 2-amino triazole/2-amino tetrazole quinoline-3-carbaldehyde, 5/4-hydroxy-6-methyl-2H-pyran-2-one, and malononitrile/methyl cyanoacetate with L-proline as a catalyst in water. Under ultrasound at 50 °C (Scheme 25) the reactions gave excellent yields (91–95%). In addition, the authors compared the performance with reflux, microwave, and ultrasonication approaches. The ultrasonic method was superior to other processes with faster reaction, greater yields, and mild conditions.

Preparation of pyrano-chromenes and benzopyrano-chromenes.

A series twleve biologically promising 2-amino-3-cyano-4H-pyran derivatives (Scheme 26) were synthesized by Sumaiya et al. in excellent yields (85–97%) (Tabassum et al., 2015). The ultrasound-accelerated cyclo-condensation in water at room temperature involved malononitrile, heteroaryl aldehyde, and various bioactive active methylene compounds using iodine catalyst. The sonochemical technique proved more efficient than the reflux and microwave processes. Fernando et al. (Auria-Luna et al., 2020) developed a simple, sonochemical protocol to assemble nineteen substituted 2-amino-3-cyano-4H-pyrans (Scheme 27) with mixed yields (44–98%). The fusion of malononitrile, substituted aldehydes and enol derivative in water at room temperature was catalyzed by trimethylamine, a Lewis base. Based on the DNA binding studies of the prepared compounds through the viscosity, circular dichroism, fluorescence, and UV–visible absorption spectroscopy measurements, the products are suitable DNA binders with excellent binding constants.

Preparation of 2-amino-3-cyano-4H-pyrans.

3.2

3.2 Chromenes

Oxygen comprising heterocyclic compounds, namely 4H-pyrans and 4H-chromene frameworks, are fascinating structures for many synthetic chemists due to their widespread prevalence in nature and capacity to exhibit varied biological activities. Chromenes are a significant class of benzopyrans, the usual constituents of many naturally occurring compounds (Li et al., 2012). Benzopyrans are bicyclic organic compounds shaped by fusing benzene with heterocyclic pyran ring (Zavar, 2017). Chromene derivatives are prominent due to their potential as biologically active analogs (Costa et al., 2016) with profitable applications in cosmetics, food additives, bio-degradable agrochemicals (Vukovic et al., 2010; Hayes et al., 2011). Chromenes and their analogs possess an extensive range of valuable anticancer, antifungal, anti-HIV, antimalarial, antifungal, antibacterial, anticoagulant, anti-tumor, anti-proliferative (El-Agrody et al., 2017), and anti-influenza properties (Puppala et al., 2016; Chen et al., 2011; Devakaram et al., 2011; Yin et al., 2013; Kakanejadifard et al., 2016; Patrusheva et al., 2016; Rival et al., 1991 ). Chromenes are also extensively used to treat schizophrenia, myoclonus (Patel et al., 2016), and down syndrome diseases (Nongrum et al., 2016; Abdolmohammadi and Balalaie, 2007).

Furthermore, 4H-chromenes are remarkable regulators for potassium cation channels and possess anticancer and anticoagulant activities (Sabry et al., 2011; Bonsignore et al., 1993). Javed et al. (Safari and Javadian, 2015) reported new magnetic Fe₃O₄-chitosan nanoparticles as a heterogeneous catalyst for producing eighteen various substituted 4H-chromene derivatives (Scheme 28) with excellent yields (94–99%) in water. The condensation of various substituted aldehydes with malononitrile and resorcinol was carried under ultrasound irradiation. The authors also studied multiple solvents, including ethanol, DMSO, DMF, acetonitrile, chloroform, and water, on a typical reaction under ultrasonic irradiation at 50 °C. The maximum yield was with water as a solvent. The role of the solvent is reportedly much significant than the power intensity for this reaction.

Fe3O4-chitosan nanoparticles catalyzed preparation of 4H-chromenes.

3.3

3.3 Chromeno[b]pyridines

Abdolmohammadi et al. (Abdolmohammadi et al., 2019) proposed a three-component reaction catalyzed via TiO₂ nanoparticles immobilized on carbon nanotubes to synthesize twelve different substituted chromeno[b]pyridine derivatives (Scheme 29) with 93–96% of the yield in water. Compared to the silent conditions, ultrasound showed a superior reaction between benzaldehyde, malononitrile, and 4-aminocoumarin. Among the solvents, water, ethanol, DMF, acetonitrile, and CH₂Cl₂, water yielded the highest product in 20 min.

4 Preparation of S & N-heterocycles in water

The MCR approach is becoming accustomed to synthesizing sulfur and nitrogen-containing heterocyclic frameworks under sonochemical conditions using water as a solvent in recent years.

4.1

4.1 Spiro [indolo-thiazepines] in water

Molecules containing different heteroatoms have substantial biological importance. Among these, 1,4-thiazepine moieties have acquired significant attention as a structural theme in medicinal chemistry due to their crucial medicinal and therapeutic actions (Marinozzi et al., 2012). Angiotensin-converting enzyme inhibition exhibited by various thiazepine derivatives (Yanagisawa et al., 1987) was the impetus for creating the Temocapril drug to treat hypertension (Arakawa et al., 2001). The physiological and biological actions of spiroindoles are of great interest. A spiro carbon connects the indole ring to a heterocyclic moiety and nitrogen or sulfur at the C-3 (Kutschy et al., 2002). Dandia et al. (Dandia et al., 2013) described a one-step three-component domino reaction using 2-mercaptoacetic acid, isatin, and 3-amino-5-methylpyrazole as precursors to construct nine substituted spiro[indole-3,4′-pyrazolo[3,4-e][1,4]thiazepines] derivatives (Scheme 30) with excellent yields (89–92%) under ultrasonic radiation at room temperature in water. This catalyst-free technique is efficient and environmentally benign.

Preparation of spiro[indole-3,4′-pyrazolo[3,4–e][1,4] thiazepines]

The spiro[indole-thiazolidine] system is a structural pattern seen in various pharmacologically significant synthetic and naturally occurring chemicals, including spiro brassinin. Their biological characteristics, including antibacterial, antileukemic, anti-inflammatory, and anticonvulsant properties, have prompted the drive for newer synthetic routes (Dandia et al., 2010). Dandia et al. (Scheme 31) (Shinde and Raskar, 2019) reported a series (47 compounds) of pharmaceutically significant spiro[indole-thiazolidinones] derivatives with 80–97% yield by a simple, water-mediated, one-step reaction. The three-component fusion involved 2-mercaptoacetic acid, isatin with different amines using a phase transfer catalyst, namely cetyltrimethylammonium bromide (CTAB), in water at room temperature by ultrasonic radiation method.

Preparation of spiro[indole-3,2′-thiazolidinone]-2,4-diones.

The thiazine framework is a particularly appealing target for combinatorial collection preparation. It is a key structure in pharmaceutical and drug preparations because of its structure–activity relationship (Azizian et al., 2000; Abhinit et al., 2009) and potential pharmacological and biological properties, namely anti-inflammatory, antimicrobial, psychotropic, anti-tumor, antioxidant, CNS and analgesic activities. Pyridothiazine and its derivatives have been a fascinating heterocyclic moiety in medication development. (Zawisza and Walinka, 1986; Malinka et al., 2004). Kapil (Arya et al., 2012) and his group synthesized ten N-substituted spiro[indole-pyrido[3,2-e]-thiazine] derivatives (Scheme 32) with impressive yields (80–92%) by one-step reaction of amines, 2-mercaptonicotinic acid, and N-substituted indole 2,3-diones in the presence of ZSM-5-([MIM]⁺BF₄⁻) catalyst under ultrasonic irradiation and water as a solvent with 80–92% yield of the final product.

Preparation of spiro[N-substituted indole-pyrido thiazines]

Ruby et al. (Singh et al., 2017) designated an efficient procedure for the creation of six spiro[acenaphthylene-thiazine]-diones (Scheme 33) with 85–89% yield at room temperature. The three-component reaction of different anilines, 3-mercaptopropionic acid, and acenaphthalene-1,2-dione in one pot in the presence of a polymer-supported catalyst (PEG–OSO₃H) under ultrasound irradiation utilize an aqueous medium.

Preparation of spiro[acenaphthylene-1,2′-[1,3]-thiazine]-2,4′-(1H)-diones.

Zang et al. (Zhang et al., 2012) reported the simple one-pot reaction for the twelve 2-benzylidenhydrazo-4-phenylthiazole derivatives (Scheme 34). The three-component reaction between different carbonyl compounds, thiosemicarbazide, and phenacyl bromide in water solvent under ultrasound radiation method at room temperature yielded 86–95% product. All twelve reactions finished in 90–240 min with a yield of 60–89% by the conventional method, while, under ultrasound, it took 50–120 min with improved harvest (86–95%).

Preparation of N-(4-arylthiazol-2-yl) hydrazones.

4.2

4.2 Thiazolidine

In 2011, Rostamnia et al. (Rostamnia and Lamei, 2011, 2011) reported a one-pot three constituent technique for preparing rhodanine derivatives. The reaction medium of using dimethyl acetylenedicarboxylate, carbon disulfide, and benzylamine under ultrasound radiation in water yielded 86–94% product. Thiazolidine is a five-membered heterocyclic moiety consisting of sulfur and nitrogen at 1 and 3 positions (Sahiba et al., 2020), which is a crucial substructure present in a range of bioactive organic compounds. It contains unique pharmacological and medicinal properties resulting from the presence of sulfur. Compounds with the thiazolidine moiety embrace a wide range of hypoglycaemic, antioxidant, anticancer, neuroprotective, antimicrobial, anti-inflammatory and anticonvulsant activities (Sandra et al., 2020). Many drugs and natural products such as teneligliptin, etozoline, lobeglitazone, and ralitoline constitute thiazolidine derivatives. Researchers have shown greater interest in efficient synthetic strategies due to their prominence.

Shaabani and Hooshmand (Shaabani and Hooshmand, 2018) reported synthesizing thirteen different rhodanine scaffolds with a 45–82% yield. The rhodanine five-membered heterocyclic compounds consist of a thiazolidine unit. The method consisted of a multicomponent one-pot sequential reaction in water under ultrasonic irradiation at room temperature (Scheme 35).

One-pot sequential preparation of pseudo-peptide containing rhodanine.

From the study, it is clear that ultrasonic irradiation increases product yields. According to the literature, the described reactions are most likely part of the first class of sonochemical responses, which occur in homogenous solutions and are accelerated and facilitated by cavitation occurrences that form reaction intermediates such as radical ions. Possibly, the incidence of cavitation for nuclei occurs faster in water than in other solvents. Water also transfers ultrasonic energy more efficiently than other solvents. Higher energy is delivered to reacting molecules with increased ultrasonic power, which accelerates the cavitation effect. Because of the scattering impact of gas bubbles on sound waves, when ultrasonic intensity exceeds the optimal value, the solution contains many gas bubbles, and lower energy is concentrated on the reaction vessel.

5 Conclusion

This review focussed on the recent literature on the ultrasound-assisted one-pot approach for synthesizing the N-, O-, and S-containing heterocyclic molecules with water as the solvent and evaluated their benefits. Ultrasound irradiation improves performance, such as reaction rate product selectivity, yield and purity and conditions. This approach eliminates the requirement of toxic catalysts and solvents. All the reactions reported exhibit obvious benefits under ultrasound irradiation in the water medium, emphasizing the capability of this unconventional and eco- and user-friendly technique in facilitating the construction of bioactive molecules. This review will impact current advancements in this area, one of the most exciting modern synthetic methodologies.

Acknowledgments

The authors are thankful to the CVR College of Engineering, Hyderabad, India, for motivating and providing the resources to complete this project. We also appreciate the research assistance provided by the University of KwaZulu-Natal, Durban, South Africa.

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Ultrasound-assisted multicomponent synthesis of heterocycles in water – A review

Abstract

Abstract

Keywords

Water as a solvent

Ultrasonic irradiation

One-Pot

Multicomponent reaction

N-, O-, and S-Heterocycles

1 Introduction

2 Preparation of N-heterocyclic compounds in water:

2.1 Pyridines and Pyrimidines:

2.2 Pyrazoles

2.3 Quinolines and their derivatives

2.4 Benzodiazepines

2.5 1,8-Dioxodecahydroacridines

2.6 Pyrroles

3 Preparation of oxygen-containing heterocycles in water:

3.1 Pyrans

3.2 Chromenes

3.3 Chromeno[b]pyridines

4 Preparation of S & N-heterocycles in water

4.1 Spiro [indolo-thiazepines] in water

4.2 Thiazolidine

5 Conclusion

Acknowledgments

References

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