SiO2: An efficient and reusable catalyst for the synthesis of oxindole derivatives

Journal of Saudi Chemical Society (2014) xxx, xxx–xxx

King Saud University

Journal of Saudi Chemical Society www.ksu.edu.sa www.sciencedirect.com

ORIGINAL ARTICLE

Nano TiO2/SiO2: An efficient and reusable catalyst for the synthesis of oxindole derivatives Maryam Haghighi, Kobra Nikoofar

*

Department of Chemistry, Alzahra University, P. O. Box 1993891176, Tehran, Iran Received 4 April 2014; revised 12 August 2014; accepted 7 September 2014

KEYWORDS Nano TiO2; Oxindole; Isatin; Indole; Reusable catalyst

Abstract Nano TiO2 supported on SiO2 (Nano TiO2/SiO2) as a solid Lewis acid, was found to be an effective and reusable catalyst for the condensation reaction of indoles with isatins to afford the corresponding bis(indolyl)oxindoles at 50 C under solvent-free conditions. The efficacy of the catalyst was also examined in the reaction of pyrrole and 3-methylindole with isatin. The catalyst has been recovered and its reusability confirmed in 5 runs. A plausible mechanism of condensation has also been suggested. ª 2014 King Saud University. Production and hosting by Elsevier B.V. All rights reserved.

1. Introduction Isatin (1-H-indole-2,3-dione) is identified as one of the most special categories of heterocyclic molecules having many notable activities including actions in the brain and offering protection against certain types of infections [1,2]. Various derivatives of isatin have been synthesized to study their chemical, biological and pharmacological activities [3]. Among these, oxindoles are noteworthy because a large number of natural products and drugs contain this heterocyclic unit [4]. They are effective as antibacterial [5], anti-inflammatory [6], antiprotozoal, laxative and new targets for cancer chemotherapy [7]. Furthermore, these heterocyclic compounds have been recently * Corresponding author. Tel./fax: +98 2188041344. E-mail addresses: [email protected], [email protected] (K. Nikoofar). Peer review under responsibility of King Saud University.

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isolated from plants [8]. The first oxindole which has been obtained from the condensation of isatin with indole is 3,3bis(indolyl)indoline-2-one that was prepared by Seidel in 1950 [9]. During recent years some methods have been reported for the condensation of some electron-rich heteroaromatics such as indoles and pyrroles with isatins to afford their oxindole derivatives. The reported procedures consist of using catalysts such as silica sulfuric acid (SSA) [10], KAl(SO4)2Æ12H2O [11], ceric ammonium nitrate (CAN) [12], phosphotungstic acid [13], montmorillonite-K10 clay [14], KSF [15], ionic liquids [16,17], Amberlyst-15 [18], prolinium triflate (ProTf) [19] and boron trifluoride supported on nano-SiO2 [20]. TiO2 (titania) is a white odourless solid which is insoluble in water and almost all organic solvents. TiO2 is chemically inert and its LD50 oral rat is upper 10,000 mg kg1 [21]. During the past decade TiO2 nanoparticles (TNPs) have received special interest due to their multiple potential applications which are widespread in industry, chemistry and medicine. Notably, it represents antibacterial effect on Escherichia coli strain [22]. Photocatalytic degradation of chlorophenols under direct solar radiation [23], catalyst support for proton exchange membrane

http://dx.doi.org/10.1016/j.jscs.2014.09.002 1319-6103 ª 2014 King Saud University. Production and hosting by Elsevier B.V. All rights reserved. Please cite this article in press as: M. Haghighi, K. Nikoofar, Nano TiO2/SiO2: An efficient and reusable catalyst for the synthesis of oxindole derivatives Journal of Saudi Chemical Society (2014), http://dx.doi.org/10.1016/j.jscs.2014.09.002

2

M. Haghighi, K. Nikoofar

fuel cells [24], producing high capacity films due to its strong light scattering [21], ingredient of printing ink [25], usage in ferrotitanium alloy and metallurgical industry [26], catalyst for Rhodamine B degradation [27], self-cleaning glass [28], usage in photovoltaic devices, sensors, and white pigment in paints [29] and filler in rubber and plastics [21] are some examples of industrial and photocatalytic activities of TNPs. Nano-TiO2 has been proved to be a good catalyst in organic chemistry because of its high activity, non-toxicity, easy availability, reusability, strong oxidizing power, Lewis acidity and long-term stability [30,31]. Some catalytic activity of titania nanoparticles has been reported in Hantzsch ester and polyhydroquinoline derivative synthesis [32], Friedel– Crafts alkylation of indoles with nitroalkanes [33], xanthene derivative synthesis [34], a-acetamido ketone [35] and bis(indolyl)methane synthesis [36], regioselective alkylation of indoles with epoxides [37], and preparation of quinoxalines [38], imines [39] and Quinazolinone derivatives [40]. Utilizing binary supporting catalysts is a great demanding necessity for organic chemists due to their expanding surface area. SiO2 (silica) is a common support for this purpose. Nano TiO2 supported on silica has recently been used for photodegradation of new Fuchsin (C.I. 42520) and Amaranth (C.I. 16185) [41] and Photocatalytic oxidation of trinitrotoluene (TNT) [42]. In continuation of our research activities on indole/isatin heterocycles [43–47] herein we report the catalytic activity of Nano TiO2/SiO2 as an impressive, inexpensive and easily handling solid Lewis acid in the synthesis of oxindole derivatives from condensation of indoles with isatins at 50 C under solvent-free conditions (Scheme 1). 2. Experimental 2.1. General Chemicals and solvents were purchased from Merck and Aldrich and used without further purifications. Commercial Nano TiO2 (APS: 10–25 nm, Purity: 99%, SSA: 200–240 m2/ gr and Bulk density: 0.24 g/cm3) in anatase phase was purchased from Nanosany corporation. N-Benzylisatin is synthesized from isatin according to the reported procedure [48]. Melting points were determined using a Stuart Scientific apparatus and are uncorrected. IR spectra (KBr disks, 500– 4000 cm1) were recorded using a Bruker FT-IR model Tensor 27 spectrometer. 1H NMR spectra were recorded in CDCl3 solvent on a Brucker 500 MHz spectrometer. Mass spectra were obtained on Platform II spectrometer from Micromass;

Figure 1 FT-IR spectra of SiO2 (a), nano TiO2 (b) and nano TiO2/SiO2 (c).

EI mode at 70 eV. Preparative layer chromatography (PLC) was carried out on 20 · 20 cm2 plates, coated with a 1 mm layer of Merck silica gel PF254, prepared by applying silica as slurry and drying in air. The scanning electron microscope P (SEM, model IJMA) was used to characterize the nano structures. 2.2. Preparation of Nano TiO2/SiO2 To a mixture of SiO2 60 (for column chromatography, mesh 70–230, 0.06–0.2 mm, 2 g) in 50 mL CHCl3, nano TiO2 (Anatase phase, 10–25 nm, 2 g) was added. The mixture was stirred at room temperature for 90 min. The solvent was evaporated at room temperature overnight to obtain a white solid of 50% (W/W) nano TiO2/SiO2. The catalyst was characterized by IR spectra (Fig. 1) and SEM image (Fig. 2).

R3

R5 R4

N

O

R2

N

Scheme 1

N

R4

R5 O +

R4 N

R1 1a-e

R3

R3 2a-d

R2 Nano TiO2/ SiO2 (0.04 g) Solvent-free, 50 oC

O N

R5

R1 3a-k

Synthesis of oxindole derivatives (3a-k) via condensation of indoles and isatins catalyzed by nano TiO2/SiO2.

Please cite this article in press as: M. Haghighi, K. Nikoofar, Nano TiO2/SiO2: An efficient and reusable catalyst for the synthesis of oxindole derivatives Journal of Saudi Chemical Society (2014), http://dx.doi.org/10.1016/j.jscs.2014.09.002

Synthesis of oxindole derivatives using nano TiO2/SiO2 2.3. General procedure for the synthesis of 3,3-bis(indolyl) oxindoles (3a-m) by nano TiO2/SiO2 under solvent-free condition A mixture of isatins 1a-e (1 mmol) and indoles 2a-e or pyrrole 4 (2 mmol) and nano TiO2/SiO2 (0.04 g) was stirred at 50 C. The progress of the reaction was monitored by TLC. After completion (15–120 min), ethylacetate (20 mL) was added and filtered. The solid residue was washed with ethylacetate (2 · 10 mL). The solvent was evaporated and the residue purified by chromatography on silica gel using n-hexane/ethyl acetate (1:1) to afford the pure products 3a-m (70–93%, Table 2, Scheme 1). All the products were characterized by comparison of their spectroscopic data (IR, 1H NMR and Mass spectra) with those of the authentic samples in the literature. 2.3.1. 3,3-Bis(2-pyrrolyl)-oxindole (3l) m.p. 173-175 C; IR (KBr): t 3351 (NH), 3261 (NH), 1710 (CO), 1618, 1462, 1078, 738 (N-H) Cm1; 1H NMR (CDCl3): d 6.02 (br s, 2H, Ar-H), 6.13-6.14 (m, 2H, Ar-H), 6.75 (s, 2H, NH), 6.94 (d, J = 7.74 Hz, 1H, Ar-H), 7.14 (t, J = 7.56 Hz, 1H, Ar-H), 7.28 (br s, 1H, NH), 7.29 (t, J = 7.88 Hz, 1H, Ar-H), 7.49 (d, J = 7.45 Hz, 1H, Ar-H), 8.67 (br s, 2H, NH) ppm; MS m/z (%) 263 (M+, 53), 220 (M+-CO and NH, 25), 153 (M+-HCO and NH and pyrrolyl, 17), 65 (pyrrolyl+, 100). 2.3.2. 3,3-Bis(3-methylindolyl)-oxindole (3m) m.p. 255–258 C; IR (KBr): t 3325 (NH), 1712 (CO), 1618, 1475, 1198, 676 (N-H) Cm1; 1H NMR (CDCl3): d 2.05 (s,

Figure 2

Table 1

3 6H, 2CH3), 6.97 (d, J = 7.35 Hz, 1H, Ar-H), 7.07–7.35 (m, 9H, Ar-H), 7.55 (d, J = 7.55 Hz, 2H, Ar-H), 8.13 (br s, 2H, NH), 8.21 (br s, 1H, NH) ppm; MS m/z (%) 391 (M+, 18), 376 (M+-CH3, 13), 348 (M+-CO and NH, 15), 332 (M+HCO and NH and CH3, 4), 261 (M+-3-methylindolyl, 20), 232 (M+-3-methylindolyl and CHO, 20), 130 (3-methylindolyl+, 100). 3. Results and discussion First, the solid catalyst nano TiO2/SiO2 has been characterized by FT-IR spectra and SEM technique. The FT-IR spectra of SiO2 (Fig. 1a), nano TiO2 (Fig. 1b) and the catalyst (Fig. 1c) have been shown. From these spectra nano TiO2/SiO2 formation was confirmed by Si–O strong vibration at 1099 cm1, Ti– O–Ti stretching vibration at 706 cm1 and weak Si–O–Ti vibration at 963 cm1 [49]. Comparison of SEM images of nano TiO2 (Fig. 2a) with those of nano TiO2/SiO2 (Fig. 2b) revealed that TiO2 nanoparticles have been supported on SiO2. To investigate the optimized reaction condition, preparation of compound 3a was performed as a model. The results are summarized in Table 1. Optimization of the temperature effect, confirmed that 50 C is appropriate (entries 1, 2 and 3). By checking various amounts of catalyst, we found that 0.04 g afforded the best results (entries 2, 4 and 5). The effect of solvent has also been examined. The data showed that solvent-free conditions are more effective (entries 4, 6 and 7). In order to be sure that the solid catalyst is more efficient than SiO2 and nano TiO2, the model reaction was verified in the

SEM image of nano TiO2/SiO2 (a) and TiO2 nanoparticles (b).

Optimization of 3,3-bis(indolyl)oxindole (3a) synthesis by nano TiO2/SiO2.a

Entry

Condition

Temp. (C)

Time (min)

Yield (%)c

1 2 3 4 5 6 7 8 9

Nano TiO2/SiO2 (0.05 g)/solvent-free Nano TiO2/SiO2 (0.05 g)/solvent-free Nano TiO2/SiO2 (0.05 g)/solvent-free Nano TiO2/SiO2 (0.04 g)/solvent-free Nano TiO2/SiO2 (0.03 g)/solvent-free Nano TiO2/SiO2 (0.04 g)/MeOH Nano TiO2/SiO2 (0.04 g)/CHCl3 Nano TiO2 (0.3 mmol)/solvent-free SiO2 (0.3 mmol)/solvent-free

80 50 r.t. 50 50 50 50 50 50

60 60 60 30 50 60 60 60 60

–b –b 72 85 80 60 55 70 60

a b c

Isatin (1 mmol) and indole (2 mmol) were used. Different products were obtained. Isolated yield.

Please cite this article in press as: M. Haghighi, K. Nikoofar, Nano TiO2/SiO2: An efficient and reusable catalyst for the synthesis of oxindole derivatives Journal of Saudi Chemical Society (2014), http://dx.doi.org/10.1016/j.jscs.2014.09.002

4

M. Haghighi, K. Nikoofar Table 2

Synthesis of oxindole derivatives (3a-k) by nano TiO2/SiO2 (0.04 g).a

Productb

R1

R2

R3

R4

R5

Time (min)

Yield (%)c

m.p. (C) found

m.p. (C) reported [Refs.]

3a 3b 3c 3d 3e 3f 3g 3h 3i 3j 3k

H H H H CH3 CH3 PhCH2 PhCH2 H H H

H H H H H H H H Br NO2 NO2

H CH3 H H H H H H H H CH3

H H CH3 H H CH3 H CH3 H H H

H H H Br H H H H H H H

30 20 15 70 40 60 120 80 90 90 100

85,83,80,80,78d 84 93 72 80 84 75 82 74 85 78

313–315 329–331 295–297 300–302 287–289 266–268 282–284 208–210 312–314 300–301 312–314

312–314 [50] 330–332 [50] 300–303 [16] 298–300 [15] 291–293 [18] 271–273 [16] 288–289 [18] 211–213 [18] 31–311 [10] 298–299 [11] >300 [17]

a b c d

Isatins (1 mmol) and indoles (2 mmol) at 50 C under solvent-free condition. All products were characterized by comparison of their spectroscopic data (FT-IR, 1H NMR) with those reported in the literature. Isolated yield. The yields of 5 runs for the catalyst reusability.

HN N H

O O +

N H

N H

Nano TiO2/ SiO2 (0.04 g) solvent-free, 50 oC

3l (120 min, 70%)

4

1a

O N H

CH3 HN O

N H 1a

Scheme 2

N H

CH3 Nano TiO2/ SiO2 (0.04 g)

O + N H

solvent-free, 50

2e

oC

O

CH3

N H 3m (70 min, 75%)

Condensation reaction of isatin (1a) with pyrrole (4) and skatole (2e) to afford oxindoles 3l and 3m.

presence of 0.03 mmol of each catalyst separately (entries 8 and 9). Comparison of the results with nano TiO2/SiO2 affirmed the particular catalytic activity of our catalyst. Therefore, performing the reaction of isatins (1 mmol), indoles (2 mmol) and nano TiO2/SiO2 (0.04 g) at 50 C under solvent-free condition has been chosen as the optimized situation for our procedure. Under optimized conditions, the reactions of various isatins (1a-e) with indoles (2a-d) were carried out until maximum progression of the reactions (Scheme 1). The results are given in Table 2. As can be seen different indole and isatin containing electron donating and withdrawing groups accomplished the condensation in good to excellent yields (70–93%) within a short reaction time (15–120 min). In the next step, we used pyrrole (4) and 3-methylindole (2e) as another sort of N-bearing heterocycles which underwent condensation reaction with isatin. It is worth mentioning that the corresponding 3,3-bis(2-pyrrolyl)oxindole (3l) and 2,2-bis(3-methylindolyl)oxindole (3m) were obtained in good

yields (Scheme 2). The result revealed the efficacy of the solid catalyst. In order to show the reusability, the model condensation of isatin (1a) with indole (2a) has been performed within 5 runs. In each step after completion of the reaction, the catalyst was filtered and washed with ethylacetate. Overnight drying at room temperature under atmosphere made the recovered solid nano TiO2/SiO2 ready for another run. The results shown in Table 2 (entry 1), confirmed that the catalyst can improve the condensation of 3a within 5 runs without decreasing the activity. On the basis of forgoing results we reported a plausible mechanism for this condensation. Nano TiO2/SiO2 activates the 3-position carbonyl group of isatin (1a) to form 5. Nucleophilic attack of indole (2a) to this structure gave the intermediate 6 that dehydrated to 7. Subsequent nucleophilic addition of another indole (2a) to 7 form 3,3-bis(indolyl)oxindole (3a) as the main product. The solid catalyst enters another condensation cycle (Scheme 3).

Please cite this article in press as: M. Haghighi, K. Nikoofar, Nano TiO2/SiO2: An efficient and reusable catalyst for the synthesis of oxindole derivatives Journal of Saudi Chemical Society (2014), http://dx.doi.org/10.1016/j.jscs.2014.09.002

Synthesis of oxindole derivatives using nano TiO2/SiO2

5

O O O N H

O

1a 5

N H

N H 2a

H N nano TiO2/SiO2

O 6

HN

+ NH

O 3a

O N H

H N

7

N H N 2a H

Scheme 3

O N H

H2O

The proposed mechanism for oxindole derivative synthesis.

4. Conclusion In this paper we have developed an efficient method for the synthesis of symmetrical oxindole derivatives using nano TiO2 supported on SiO2 as a heterogeneous, readily available, reusable and eco-friendly solid acid catalyst at ambient temperature under solvent-free conditions. Simple experimental procedure associated with high yield and short reaction times makes this protocol interesting for organic chemists. The reusability of the catalyst is a highlight point in the reported method. Acknowledgments The authors are grateful to the Research Council of Alzahra University for the financial support of this work. References [1] S.N. Pandeya, S. Smitha, M. Jyoti, S.K. Sridhar, Biological activities of isatin and its derivatives, Acta Pharm. 55 (2005) 27– 46. [2] K.L. Viene, L. Matesic, J.M. Locke, M. Ranson, D. Skropeta, Cytotoxic and anticancer activities of isatin and its derivatives: a comprehensive review from 2000–2008, Anticancer Agents 9 (2009) 397–414. [3] T.-H. Kang, K. Matsumoto, M. Tohda, Y. Murakami, H. Takayama, M. Kitajima, N. Aimi, H. Watanabe, Pteropodine and isopteropodine positively modulate the function of rat muscarinic M1 and 5-HT2 receptors expressed in Xenopus oocyte, Eur. J. Pharmacol. 444 (2002) 39–45. [4] S.J. Garden, J.C. Torres, A.A. Ferreira, R.B. Silva, A.C. Pinto, A modified sandmeyer methodology and the synthesis of (±)convolutamydine, Tetrahedron Lett. 38 (1997) 1501–1504.

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Please cite this article in press as: M. Haghighi, K. Nikoofar, Nano TiO2/SiO2: An efficient and reusable catalyst for the synthesis of oxindole derivatives Journal of Saudi Chemical Society (2014), http://dx.doi.org/10.1016/j.jscs.2014.09.002