Green Synthesis of Chalcone Derivatives Using Chalcones as Precursor

*Surbhi Dhadda, Prakash Giri Goswami and Himanshu Sharma*

#### **Abstract**

Recently, the use of green methodologies like sonication, use of ionic liquids, etc. attracted the attention of researchers in the field of organic synthesis as they have advantages such as mild reaction conditions, environmentally benign procedures, etc. Herein, this chapter highlights some recyclable ionic liquids (ILs) catalyzed ring closure reactions of chalcones to obtain several heterocyclic rings viz.; pyrazoles, pyrans, pyrimidines under ultrasonification. These reactions have very important features i.e., short routine, high yields, being environmentally friendly, high functional group tolerance, formation of a single product, high atom economy, high yielding, no need for column purification, etc. The various synthesized compounds were prepared in optimized reaction conditions in good to efficient yields. Analytical and spectral (FTIR, <sup>1</sup> H, and 13C NMR) techniques were employed for the structural elucidation of the synthesized compounds. The ionic liquids used in the synthesis are recycled and reused several times.

**Keywords:** Chalcones, green synthesis, ionic liquid, ring closure reactions, sonication

#### **1. Introduction**

In recent years, the emphasis of science and technology has shifted more toward environmental benign and sustainable resources and progress. Green Chemistry is paramount concept in chemistry for sustainability, which is the implementation of a set of principles that minimize or get rid of the utilization or generation of hazardous substances in the design, manufacture, and applications of chemical products [1]. Presently, Sonochemistry is a simplistic pathway for a huge variety of syntheses in organic chemistry. Hence, significant features of the ultrasound approach compared with traditional methods are in higher yields, milder conditions, lesser reaction times, improved reaction rates, formation of purer products, easier manipulation and a role in waste minimization and energy protection [2–5].

Multicomponent reactions [6] leading to facinating heterocyclic scaffolds must appear as Potent tools for delivering the molecular diversity required in combinatorial approaches for the synthesis of bioactive compounds and producing varied chemical

libraries of drug-like molecules for biological screening [7, 8]. Chalcones, or 1,3 diphenyl-2-propen-1-ones, are commonly occurring heterocyclic ring systems and are important structural motifs found in many natural products and pharmaceuticals. It is also known as benzalacetophenone and benzylidene acetophenone. Chalcones are one of the most important classes of flavonoids [9, 10]. Further ring closure reactions of Chalcones can be used to obtain various heterocyclic rings viz.; Pyrazoles, Pyrans, Cyanopyridines, isoxazoles and pyrimidines having different hetero-cyclic ring systems and multiple derivatives can be synthesized using chalcones [11–15].

The increased environmental concerns needed the replacement of present methods with new more sustainable processes which used the ionic liquids in place of organic catalysts and solvents [16–25]. Ionic Liquids (ILs), as a class of molten salts, are composed entirely of ions and their melting point is around or below 100°C [26–36]. Due to short reaction times, mild reaction conditions, better yields, easy recyclability thermally stable, non-flammable character with negligible vapor pressure, adjustable miscibility with organic substrates and tunable solvating ability ionic liquids (ILs) have attracted the attention of organic chemists [37–49]. Furthermore, unique physiochemical properties that make them potential candidates for many applications in pharmaceuticals, industry and academia [50–52].

There are several varieties of ionic liquids being studied, out of them a few Simple functionalized ILs have created unparalleled fascination as they display some benefits for certain base-catalyzed processes, like easy recycling and better catalytic performance [53]. The environmentally benign basic ionic liquids are used as reaction media as well as catalysts in the development of multicomponent reactions (MCRs). Among all such basic ionic ILs [DBU][OAc] has shown the desired results. Some of the key benefits that can be highlighted for utilization of this IL as catalyst are, the desired product obtained without any further purification and the recyclability of the catalyst was found to be up to 5 cycles. The investigation of alternatives with the help of ionic liquids to conventional organic solvents is a developing research area due to increased environmental concerns.

Herein, we are especially interested in developing the potential use of efficient, simple methodology for the ring closure reactions of chalcones using [DBU][OAc] as ionic liquids as a solvent and catalyst. Chalcones can be used to obtain various heterocyclic rings through ring closure reactions (**Figure 1**).

**Figure 1.** *General scheme of ring closure reactions of chalcones.*

#### **2. Experimental section**

#### **2.1 Materials and methods**

Melting points were recorded in open glass capillary tube using Gallenkamp melting point apparatus and are uncorrected. Checked by Thin layer chromatography (TLC) was applied to check the purity of synthesized compounds and Spots were visualized by irradiation with UV lights (254 nm) or by staining with iodine vapors. The Fourier-transform infrared (FT-IR) spectra were recorded on SHIMADZU 8400S FT-IR spectrophotometer and wave number is given in cm<sup>1</sup> . The <sup>1</sup> H NMR spectra and 13C NMR (by broad band proton decoupling technique) were recorded on JEOL AL spectrometer in CDCl3/DMSO-d6 solvents at 400 and 100 MHz and chemical shift were measured in δ ppm relative to TMS as an internal standard. The Mass (HRMS) spectra were recorded on JEOL SX 102/DA-600 using Argon/Xenon gas. The elemental analysis (C, H and N) were performed using vario-III analyzer at CDRI Lucknow.

#### **2.2 General procedure for preparation of DBU based ionic liquid**

According to the reported literature [DBUH][OAc] ILs [54] and [DBUH][Cl] ILs [55] were synthesized by the reaction of 2,3,4,6,7,8,9,10-octahydropyrimido[1,2-a] azepine (DBU) and acetic acid or hydrochloric acid, respectively.

#### **2.3 General procedure for preparation of chalcones (3a-c)**

Chalcones were synthesized according to the reported procedure with minor modification (**Figure 2**), the synthesized products were characterized by <sup>1</sup> H NMR, and physical data and compared with those reported in literature [54].

**Figure 2.** *General procedure of synthesis of chalcones (3a-c).*

#### **2.4 Model reaction for preparation of pyrazole derivative (4a)**

Chalcone derivative (1 mmol) and methylhydrazine (1 mmol) were ultrasonicated catalyzed by [DBUH][OAc] (5 ml) at 50°C for about 4 h (**Figure 3**). The crude product was refrigerated overnight. The precipitate formed was filtered off and crystallized from ethanol yielding yellow crystals of the product (4a).

**Figure 3.** *Model reaction for preparation of pyrazole derivative (4a).*

*2.4.1 Spectroscopic data of (4a)*

1 H NMR (400 MHz, DMSO-d6) δ 8.81, 7.94, 7.59, 7.47, 7.44, 7.38, 3.96; 13C NMR (100.15 MHz, DMSO-d6) δ 145.51, 133.32, 131.99, 130.37, 129.66, 128.69, 128.34, 126.78, 125.67, 123.12, 122.13, 40.57; HRMS; *m*/*z* 312.04 (M+); C16H13BrN2: calcd. C, 61.36; H, 4.18; N, 8.94; found C, 61.34; H, 4.20; N, 8.97.

#### **2.5 Model reaction for preparation of pyran derivative (5a)**

Chalcone derivative (1 mmol) mixed with *α,β*-diketone (1 mmol) was ultrasonicated in [DBUH][OAc] (5 mL) for about 45 minutes. The mixture was heated to 60°C for 2 h to complete the reaction which was monitored by TLC. The organic layer was extracted with ethyl acetate, washed with water and then dried over Na2SO4 which was followed by filtration and concentration. The crude was recrystallized from ethyl acetate and hexane mixture to give pure product (5a). The catalyst remained in the aqueous phase was reused in other reactions (**Figure 4**).

**Figure 4.** *Model reaction for preparation of pyran derivative (5a).*

#### *2.5.1 Spectroscopic data of (5a)*

1 H NMR (400 MHz, DMSO-d6) δ 7.45, 7.32, 7.28, 7.25, 7.01, 5.27, 3.60, 2.28, 2.21, 2.12, 2.05; 13C NMR (100.15 MHz, DMSO-d6) δ 195.02, 164.92, 142.45, 138.87, 131.92, 129.14, 128.97, 128.27, 128.12, 122.84, 107.13, 76.87, 35.62, 35.14, 27.61, 16.76; HRMS; *m*/*z* 370.01 (M+); C20H19BrO2: calcd. C, 64.72; H, 5.17; found C, 64.75; H, 5.21.

#### **2.6 Model reaction for preparation of cyanopyridine derivative (6a)**

A mixture of chalcone derivative (2 mmol) with malononitrile (2 mmol) in 5 mL of [DBUH][OAc] was ultrasonicated at atmospheric pressure at 65°C for 3 h (**Figure 5**). After completion of the reaction, the mixture was cooled to room temperature and the organic layer was concentrated. The pure product was obtained by column chromatography (n-hexane:ethyl acetate = 80:20) to afford the preferred product (6a).

**Figure 5.** *Model reaction for preparation of cyanopyridine derivative (6a).*

*2.6.1 Spectroscopic data of (6a)*

1 H NMR (400 MHz, DMSO-d6) δ 9.21, 8.40, 7.95, 7.62, 7.51, 7.44, 7.46; 13C NMR (100.15 MHz, DMSO-d6) δ 160.21, 152.79, 151.01, 138.51, 138.45, 131.34, 130.03, 129.67, 128.99, 127.91, 121.91, 120.71, 117.22, 110.19; HRMS; *m*/*z* 334.06 (M+); C18H11BrN2: calcd. C, 64.52; H, 3.35; N, 8.37; found C, 64.49; H, 3.33; N, 8.36.

#### **2.7 Model reaction for preparation of isoxazole derivative (7a)**

Chalcone derivative (1 mmol) was ultrasonicated with hydroxylamine hydrochloride (1 mmol) in catalytic influence of [DBUH][OAc] ILs (5 mL) at 70°C for 1 h (**Figure 6**). The formation of product was monitored by TLC. Isoxazole derivative was obtained by keeping the reaction mixture on ice bath, then the desired product was isolated, washed with water, and dried (7a).

**Figure 6.**

*Model reaction for preparation of isoxazole derivative (7a).*

*2.7.1 Spectroscopic data of (7a)*

1 H NMR (400 MHz, DMSO-d6) δ 8.66, 7.69, 7.57, 7.50, 7.41, 7.32; 13C NMR (100.15 MHz, DMSO-d6) δ 170.26, 154.95, 131.82, 130.67, 128.61, 128.30, 128.07, 127.55, 126.73, 125.41, 116.74; HRMS; *m*/*z* 299.04 (M+); C15H10BrNO: calcd. C, 60.01; H, 3.37; N, 4.69; found C, 60.03; H, 3.39; N, 4.71.

#### **2.8 Model reaction for preparation of pyrimidine derivative (8a)**

To the mixture of chalcone derivative (1 mmol), guanidine hydrochloride (2 mmol) was added with [DBUH][OAc] ILs was heated under ultrasonication for 2 h at 55°C. The completion of the reaction was checked by TLC (**Figure 7**). The reaction mixture poured into ice water and formed product was filtered and recrystallized from ethanol (8a).

**Figure 7.** *Model reaction for preparation of pyrimidine derivative (8a).*

*2.8.1 Spectroscopic data of (8a)*

1 H NMR (400 MHz, DMSO) δ 7.77, 7.64, 7.47, 7.41, 7.15, 2.29; 13C NMR (100.15 MHz, DMSO-d6) δ 160.02, 158.70, 138.09, 136.17, 132.01, 131.05, 130.28,

#### **Figure 8.**

*General representation of preparation of chalcone derivatives (4-8a-c).*

129.20, 128.35, 125.47, 112.89; HRMS; *m*/*z* 325.05 (M+); C16H12BrN3: calcd. C, 58.93; H, 3.72; N, 12.90; found C, 58.97; H, 3.70; N, 12.91 (see **Figure 8**).

#### **3. Results and discussion**

In this chapter, the ring closure reaction of chalcone derivatives in the presence of basic ionic liquid [DBUH]OAc to afford the several derivatives like pyrazoles, pyrans, pyrimidines, isoxazoles, and cyanopyridines*.* Different catalytic systems were used to optimize the reaction conditions on the set of model reactions.

#### **3.1 Optimization of reaction conditions**

The reaction conditions were optimized on the respective model reactions, further these optimized reaction conditions were used to produce corresponding derivatives of chalcones (**Table 1**).

We have carried out the synthesis of a number of chalcone derivatives (4-8a,b,c) under different reaction conditions. The optimized conditions for all the ring closure reactions of chalcones involved use of [DBUH]OAc ILs as catalyst under sonication for appropriate time at adequate temperature (**Table 2**, Entry 6).

*Green Synthesis of Chalcone Derivatives Using Chalcones as Precursor DOI: http://dx.doi.org/10.5772/intechopen.103959*

*Green Synthesis of Chalcone Derivatives Using Chalcones as Precursor DOI: http://dx.doi.org/10.5772/intechopen.103959*



**Table 2.**

*Optimization of reaction conditions.*

#### **3.2 Reusability of ionic liquids**

The catalytic reusability of ILs was observed during optimized reaction conditions. The ILs were easily recovered as filtration after the completion of reaction. The recovered ILs were used four times without remarkable loss in activity but after that there is sudden decrease (**Figure 9**) in yield of products.

**Figure 9.** *Reusability and recyclability of [DBUH]OAc ILs.*

#### **4. Conclusion**

In Summary, we developed a simple and efficient catalytic system that can effectively promote the conversion of chalcones into different derivatives viz.; Pyrazoles, Pyrans, Cyanopyridines, isoxazoles and pyrimidines *via* [DBU][OAc] IL catalyzed ring closure reactions under mild conditions. A series of functional ILs was screened and [DBU][OAc] was determined as the optimal catalyst. This mild and environmental friendly synthetic methodology permitted us to synthesize products in good to excellent yields. There are many merits of the used protocol like, low cost of green catalyst, operational simplicity, obtaining products in high yield, and the catalyst can be reused without any significant loss of catalytic property up to five catalytic cycles.

*Green Synthesis of Chalcone Derivatives Using Chalcones as Precursor DOI: http://dx.doi.org/10.5772/intechopen.103959*

#### **Author details**

Surbhi Dhadda<sup>1</sup> , Prakash Giri Goswami<sup>2</sup> and Himanshu Sharma<sup>3</sup> \*

1 Department of Chemistry, Vedic Kanya P.G. College, Jaipur, Rajasthan, India

2 Department of Chemistry, University of Rajasthan, Jaipur, Rajasthan, India

3 Department of Chemistry, Mohanlal Sukhadiya University, UCOS, Microwave Chemistry Lab, Udaipur, Rajasthan, India

\*Address all correspondence to: himanshu@mlsu.ac.in

© 2022 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

## **References**

[1] Hua Y, Zou Y, Wu H, Shi D. A facile and efficient ultrasound-assisted synthesis of novel dispiroheterocycles through 1, 3-dipolar cycloaddition reactions. Ultrasonics Sonochemistry. 2012;**19**:264-269

[2] Zbancioc G, Florea O, Jones PG, Mangalagiu II. An efficient and selective way to new highly functionalized coronands or spiro derivatives using ultrasonic irradiation. Ultrasonics Sonochemistry. 2012;**19**:399-403

[3] Wang SY, Ji SJ, Loh TP. The Michael addition of indole to α,β-unsaturated ketones catalyzed by iodine at room temperature. Synlett. 2003;**15**:2377-2379

[4] Dandia H, Singh R, Bhaskaran S. Ultrasound promoted greener synthesis of spiro[indole-3,5<sup>0</sup> -[1,3]oxathiolanes] in water. Ultrasonics Sonochemistry. 2010; **17**:399-402

[5] Nair V, Rajesh C, Vinod AU, Bindu S, Sreekanth AR, Mathen JS, et al. Strategies for heterocyclic construction via novel multicomponent reactions based on isocyanides and nucleophilic carbenes. Accounts of Chemical Research. 2003;**36**:899-907

[6] Dömling A. Recent advances in isocyanide-based multicomponent chemistry. Current Opinion in Chemical Biology. 2002;**6**(3):306-313

[7] Babu AS, Raghunathan R. Ultrasonic assisted-silica mediated [3+ 2] cycloaddition of azomethine ylides—A facile multicomponent one-pot synthesis of novel dispiroheterocycles. Tetrahedron Letters. 2007;**48**(38): 6809-6813

[8] Ni L, Meng CQ, Sikorski JA. Recent advances in therapeutic chalcones.

Expert Opinion on Therapeutic Patents. 2004;**14**(12):1669-1691

[9] Sahu NK, Balbhadra SS, Choudhary J, Kohli DV. Exploring pharmacological significance of chalcone scaffold: A review. Current Medicinal Chemistry. 2012;**19**:209-225

[10] El-Hashah MA, El-Kady M, Saiyed MA, Elaswy AA. Arylidene derivatives as synthons heterocyclic synthesis. Egyptian Journal of Chemistry. 1985;**27**:715

[11] Crawley LS, Fanshawe WJ. Neighboring group participation in cyclodehydration. A regiospecific isoxazole synthesis. Journal of Heterocyclic Chemistry. 1977;**14**(3): 531-534

[12] Taylor EC, Morrison RW Jr. An unusual molecular rearrangement of an N-aminopyrimidine. The Journal of Organic Chemistry. 1967;**32**(8):2379-2382

[13] Utale PS, Raghuwanshi PB, Doshi AG. Synthesis of some new 1- Carboxamido-3-(substituted-2-hydroxy phenyl)-5-aryl-[delta] 2-pyrazolines. Asian Journal of Chemistry. 1998;**10**(3): 597-599

[14] Kidwai M, Misra P. Ring closure reactions of chalcones using microwave technology. Synthetic Communications. 1999;**29**(18):3237-3250

[15] Le ZG, Chen ZC, Hu Y, Zheng QG. Organic reactions in ionic liquids: A simple and highly regioselective Nsubstitution of pyrrole. Synthesis. 2004; **12**:1951-1954

[16] Nara SJ, Naik PU, Harjani JR, Salunkhe MM. Potential of ionic liquids in greener methodologies involving

*Green Synthesis of Chalcone Derivatives Using Chalcones as Precursor DOI: http://dx.doi.org/10.5772/intechopen.103959*

biocatalysis and other synthetically important transformations. Indian Journal of Chemistry. 2006;**45B**: 2257-2269

[17] Catal KN. Rev. synthesis of fivemembered N-heterocycles fused with other heterocycles. Catalysis Reviews. 2015;**57**(1):1-78

[18] Kaur N, Kishore D, Kaur N, Kishore D. Microwave-assisted synthesis of six-membered O-heterocycles. Synthetic Communications. 2014; **44**(21):3047-3081

[19] Kaur N, Dwivedi J, Kishore D, Kaur N, Dwivedi J, Kishore D. Solidphase synthesis of nitrogen-containing five-membered heterocycles. Synthetic Communications. 2014;**44**(12): 1671-1729

[20] Nair V, Vellalath S, Poonoth M, Suresh E, Viji S. N-heterocyclic carbene catalyzed reaction of enals and diaryl-1, 2 diones via homoenolate: Synthesis of 4, 5, 5-trisubstituted γ-butyrolactones. Synthesis. 2007;**20**:3195-3200

[21] Potewar TM, Siddiqui SA, Lahoti RJ, Srinivasan KV. Efficient and rapid synthesis of 1-substituted-1H-1, 2, 3, 4 tetrazoles in the acidic ionic liquid 1-nbutylimidazolium tetrafluoroborate. Tetrahedron Letters. 2007;**48**(10): 1721-1724

[22] Xu JM, Qian C, Liu BK, Wu Q, Lin XF. A fast and highly efficient protocol for Michael addition of Nheterocycles to α, β-unsaturated compound using basic ionic liquid [bmIm] OH as catalyst and green solvent. Tetrahedron. 2007;**63**(4): 986-990

[23] Hutka M, Toma S. Hydrogentransfer reduction of aromatic ketones in basic ionic liquids. Monatshefte für

Chemie-Chemical Monthly. 2009; **140**(10):1189-1194

[24] Syamala M. Recent progress in three-component reactions. An update. Organic Preparations and Procedures International. 2009;**41**(1):1-68

[25] Wasserscheid P, Keim W. Ionic liquids—New "solutions" for transition metal catalysis. Angewandte Chemie International Edition. 2000;**39**:3772-3789

[26] Frizzo CP, Tier AZ, Bender CR, Gindri IM, Villetti MA, Zanatta N, et al. Structural and Physical Aspects of Ionic Liquid Aggregates in Solution. InIonic Liquids-Current State of the Art Rijeka. London, UK: InTech; 2015. pp. 161-198

[27] Berthod A, Ruiz-Angel MJ, Carda-Broch S. Recent advances on ionic liquid uses in separation techniques. Journal of Chromatography A. 2018;**1559**:2-16

[28] Javed MN, Muhammad S, Hashmi IA, Bari A, Musharraf SG, Ali FI. Newly designed pyridine and piperidine based ionic liquids: Aggregation behavior in ESI-MS and catalytic activity in CC bond formation reactions. Journal of Molecular Liquids. 2018;**272**: 84-91

[29] Kaur N. Environmentally benign synthesis of five-membered 1, 3-N, Nheterocycles by microwave irradiation. Synthetic Communications. 2015;**45**(8): 909-943

[30] Kaur N. Advances in microwaveassisted synthesis for five-membered N-heterocycle synthesis. Synthetic Communications. 2015;**45**(4): 432-457

[31] Kaur N. Microwave-assisted synthesis of five-membered Sheterocycles. Journal of the Iranian Chemical Society. 2014;**11**(2):523-564 [32] Kaur N. Review on the synthesis of six-membered N, N-heterocycles by microwave irradiation. Synthetic Communications. 2015;**45**(10):1145-1182

[33] Kaur N. Greener and expeditious synthesis of fused six-membered N, Nheterocycles using microwave irradiation. Synthetic Communications. 2015;**45**(13):1493-1519

[34] Kaur N. Applications of microwaves in the synthesis of polycyclic sixmembered N. N-heterocycles. Synthetic Communications. 2015;**45**(14):1599-1631

[35] Kaur N. Synthesis of five-membered N, N, N-and N, N, N, N-heterocyclic compounds: Applications of microwaves. Synthetic Communications. 2015;**45**(15):1711-1742

[36] Bao Q, Qiao K, Tomida D, Yokoyama C. Preparation of 5 hydroymethylfurfural by dehydration of fructose in the presence of acidic ionic liquid. Catalysis Communications. 2008; **9**(6):1383-1388

[37] Shen J, Wang H, Liu H, Sun Y, Liu Z. Brønsted acidic ionic liquids as dual catalyst and solvent for environmentally friendly synthesis of chalcone. Journal of Molecular Catalysis A: Chemical. 2008; **280**(1–2):24-28

[38] Wang W, Shao L, Cheng W, Yang J, He M. Brønsted acidic ionic liquids as novel catalysts for Prins reaction. Catalysis Communications. 2008;**9**(3): 337-341

[39] Kaur N. Role of microwaves in the synthesis of fused five-membered heterocycles with three N-heteroatoms. Synthetic Communications. 2015;**45**(4): 403-431

[40] Kaur N. Recent impact of microwave-assisted synthesis on benzo derivatives of five-membered Nheterocycles. Synthetic Communications. 2015;**45**(5):539-568

[41] Kaur N, Kishore D. Microwaveassisted synthesis of seven-and highermembered N-heterocycles. Synthetic Communications. 2014;**44**(18): 2577-2614

[42] Kaur N, Kishore D. Microwaveassisted synthesis of six-membered Sheterocycles. Synthetic Communications. 2014;**44**(18): 2615-2644

[43] Kaur N, Kishore D. Microwaveassisted synthesis of seven-and highermembered O-heterocycles. Synthetic Communications. 2014;**44**(19): 2739-2755

[44] Luo S, Mi X, Zhang L, Liu S, Xu H, Cheng JP. Functionalized ionic liquids catalyzed direct aldol reactions. Tetrahedron. 2007;**63**(9):1923-1930

[45] Carvalho PJ, Álvarez VH, Marrucho IM, Aznar M, Coutinho JA. High pressure phase behavior of carbon dioxide in 1-butyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide and 1-butyl-3- methylimidazolium dicyanamide ionic liquids. The Journal of Supercritical Fluids. 2009;**50**(2):105-111

[46] Holbrey JD, Reichert WM, Reddy R, Rogers R. Ionic Liquids as Green Solvents: Progress and Prospects, ACS Symposium Series. Washington, DC: American Chemical Society; 2003. pp. 121-133

[47] Cevasco G, Chiappe C. Are ionic liquids a proper solution to current environmental challenges. Green Chemistry. 2014;**16**:2375-2385

[48] Yang Z, Pan W. Ionic liquids: Green solvents for nonaqueous biocatalysis.

*Green Synthesis of Chalcone Derivatives Using Chalcones as Precursor DOI: http://dx.doi.org/10.5772/intechopen.103959*

Enzyme and Microbial Technology. 2005;**37**(1):19-28

[49] Mecerreyes D. Polymeric ionic liquids: Broadening the properties and applications of polyelectrolytes. Progress in Polymer Science. 2011;**36**(12): 1629-1648

[50] Mishra N, Arora P, Kumar B, Mishra LC, Bhattacharya A, Awasthi SK, et al. Synthesis of novel substituted 1, 3 diaryl propenone derivatives and their antimalarial activity in vitro. European Journal of Medicinal Chemistry. 2008; **43**(7):1530-1535

[51] Awasthi SK, Mishra N, Kumar B, Sharma M, Bhattacharya A, Mishra LC, et al. Potent antimalarial activity of newly synthesized substituted chalcone analogs in vitro. Medicinal Chemistry Research. 2009;**18**(6):407-420

[52] Hajipour AR, Rafiee F. Basic ionic liquids. A short review. Journal of the Iranian Chemical Society. 2009;**6**(4): 647-678

[53] Ying AG, Liu L, Wu GF, Chen G, Chen XZ, Ye WD. Aza-Michael addition of aliphatic or aromatic amines to α, βunsaturated compounds catalyzed by a DBU-derived ionic liquid under solventfree conditions. Tetrahedron Letters. 2009;**50**(14):1653-1657

[54] Tolstikova LL, Shainyan BA. Ionic liquids on the basis of 2, 3, 4, 6, 7, 8, 9, 10-octahydropyrimido-[1, 2-a] azepine (1, 8-diazabicyclo [5.4. 0] undec-7-ene). Russian Journal of Organic Chemistry. 2006;**42**:1068-1074

[55] Li J, Zhuang R, Qian Y. Synthesis of novel Chalcone derivatives by organic catalysis. Materials Physics and Chemistry. 2019;**1**(1):1-564

#### **Chapter 4**
