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Beilstein Organic Chemistry Symposium 2015


 
 

C-Arylation reactions catalyzed by CuO-nanoparticles under ligand free conditions

Mazaahir Kidwai, Saurav Bhardwaj and Roona Poddar
Green Research Laboratory, Department ofChemistry, University of Delhi, Delhi, India 110007
Email of corresponding author Corresponding author email     
Associate Editor: I. Marek
Beilstein J. Org. Chem. 2010, 6, No. 35.
doi:10.3762/bjoc.6.35
 
 
 
 

Abstract

CuO-nanoparticles were found to be an excellent heterogeneous catalyst for C-arylation of active methylene compounds using various aryl halides. The products were obtained in good to excellent yield. The catalyst can be recovered and reused for four cycles with almost no loss in activity.

Keywords: active methylene compounds; C-arylation; heterogeneous catalyst; recyclability

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Introduction

Carbon-carbon (C–C) bond formation is one of the most important reactions in organic synthesis [1-3]. The resulting compounds formed from C–C coupling are valuable synthons in organic synthesis [4-7]. However, C-arylation reactions have not been investigated to the same extent as other C–C bond forming reactions.

A great deal of attention has been focused on the development of Pd catalyzed arylation [8-11]. Another important protocol involves arylation of activated methylene compounds mediated by copper salts [12,13]. Recently, proline has also been used along with CuI for C-arylation [14]. But some of the methods suffer from serious drawbacks and limitations, for example, long reaction times [15,16], the high cost of Pd catalysts [17,18] and the need for stoichiometric amounts of copper salts. In addition to these problems, the major drawback is that the majority of catalysts cannot be reused [19]. To overcome from these problems, we have investigated a new catalytic system for C-arylation.

Nanocrystalline metal oxides find numerous applications, e.g., as active adsorbents for gases [20], the destruction of hazardous materials [21] and the oxidation of volatile organic compounds [22]. In addition, metal oxide nanoparticles have been used as heterogeneous catalysts for various organic transformations [23-28]. The high reactivity of CuO-nanoparticles (CuO-np) is due to the high surface area of nanoparticles combined with unusual reactive morphologies. Moreover, heterogeneous catalysts are easy to separate and can be recycled. This is very beneficial for industrial process in the green chemistry domain.

In continuation with our research program to explore different methodologies for the synthesis of organic compounds [29,30] and the role of transition metal nanoparticles as catalysts in organic reactions [31-33], we now report the synthesis of 3-arylpentane-2,4-diones and diethyl 2-aryl-malonates using CuO-nanoparticles as a heterogeneous catalyst.

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Results and Discussion

The reaction was carried out several times in order to establish the optimum ratio of reactants. Iodobenzene and acetylacetone were employed as model substrates in a 1:3 ratio. When the iodobenzene (1 mmol) and acetylacetone (3 mmol) were stirred with Cs2CO3 (0.5 mmol) at 80 °C in DMSO, in the presence of CuO-nanoparticles (10 mol %), 3-phenyllpentane-2,4-dione was obtained in 80% yield (Scheme 1).

[1860-5397-6-35-i1]
Scheme 1: Synthesis of 3-phenylpentane-2,4-dione using CuO-nanoparticles.

Other copper salts such as Cu(OAc)2 and ordinary CuO were found to be inferior to CuO-nanoparticles and gave low yields of 3-phenylpentane-2,4-dione. Moreover, Cu-nanoparticles which have been used for O-arylation and S-arylation [34,35], were not effective in the coupling reaction (Table 1).

Table 1: C-arylation reaction catalyzed by different Cu catalystsa.
EntryCatalystTime (h)Yieldb (%)
1Cu(OAc)21020
2Cu-np1010
3CuO1024
4CuO-np880

In addition, catalytic activity of CuO-nanoparticles was evident since no product was formed in its absence. The increased catalytic activity of CuO-nanoparticles over the commercially available bulk CuO may be attributed to the higher surface area of CuO-nanoparticles. This is thought to be due to morphological differences which have been shown in the TEM image. The number of reactive sites on the surface is small in the case of larger crystallites and considerably greater in the case of smaller crystallites (Figure 1).

[1860-5397-6-35-1]
Figure 1: Powder X-ray diffraction pattern and TEM image of nano CuO (fresh).

To investigate further the surface morphology of CuO-nanoparticles, powder XRD and TEM images were taken. Figure 1 shows the XRD pattern of CuO-nanoparticles in which diffraction peaks can be indexed to a monoclinic structure. The intense diffraction peak at an angle 38.4 shows index plane (111) which contains more basic sites with higher density as compared to bulk CuO.

During optimization of reaction conditions, the model reaction was carried out in different solvents. It was found that DMSO was the most effective solvent compared to the other solvents used as shown in Table 2. This is not surprising in view of the fact that the reaction intermediate is a carbanion and therefore will have a greater stability in a polar solvent.

Table 2: CuO-nanoparticles catalyzed coupling reaction of acetylacetone and iodobenzene in various solventsa.
EntrySolventTime (h)Yieldb (%)
1DMSO880
2Toluene158
3THF1512
4Acetonitrile1532

Moreover, the advantage of the nanoparticles is that, unlike other catalysts, their use is not restricted by their solubility, as the nanoparticles can be dispersed in the desired solvent by agitation or slight sonication.

When an equimolar mixture of chlorobenzene and iodobenzene was treated with acetylacetone under similar reaction conditions, the chlorobenzene was largely unreactive. This shows that the reaction is highly selective towards the halogen present in the aryl halide (Scheme 2).

[1860-5397-6-35-i2]
Scheme 2: Synthesis of 3-phenylpentane-2,4-dione using CuO-nanoparticles.

To study the scope of this procedure, acetylacetone was reacted with various aryl halides and gave the corresponding products in 78–83% yield. It was observed that aryl halides having electron withdrawing groups showed greater reactivity and gave good yield of products compared to aryl halides having electron donating groups. All these results are summarized in Table 3.

Table 3: C-arylation of acetylacetone using different aryl halidesa
EntryAryl halideProductTime (h)Yieldb (%)
1iodobenzene3-phenylpentane-2,4-dione880
2bromobenzene3-phenylpentane-2,4-dione1079
3p-nitroiodobenzene3-(4-nitrophenyl)-pentane-2,4-dione683
4p-methyliodobenzene3-p-tolylpentane-2,4-dione1078
5m-trifluoromethyliodobenzene3-(3-trifluromethyl-phenyl)-pentane-2,4-dione781
61-iodo-2-methylbenzene3-o-tolyl-pentane-2,4-dione1176
71-iodo-4-methoxybenzene3-(4-methoxy-phenyl)-pentane-2,4-dione1275

The above results encouraged us to investigate further reactions. Under similar reaction conditions, diethyl malonate was treated with iodobenzene to give the desired product in 78% yield (Scheme 3). The reaction was then repeated with a variety of aryl halides. The results are summarized in Table 4.

[1860-5397-6-35-i3]
Scheme 3: Synthesis of diethyl 2-aryl-malonate using CuO-nanoparticles.
Table 4: C-arylation of diethyl malonate using different aryl halidesa.
EntryAryl halideProductTime (h)Yieldb (%)
1iodobenzene2-phenylmalonic acid diethylester978
2bromobenzene2-phenylmalonic acid diethylester1176
3p-nitroiodobenzene2-(4-nitrophenyl)-malonic acid diethylester681
4p-methyliodobenzene2-p-tolylmalonic acid diethylester1276
5m-trifluoromethyliodobenzene2-(3-trifluromethyl-phenyl)-malonic acid diethylester780
61-iodo-2-methylbenzene2-o-tolylmalonic acid diethylester1375
71-iodo-4-methoxybenzene3-(4-methoxy-phenyl)-malonic acid diethylether1474

The observed decrease in reactivity in the order p-nitroiodobenzene > iodobenzene > p-methyliodobenzene > 1-iodo-4-methoxybenzene suggests that the reaction proceeds by oxidative addition followed by reductive elimination. In addition to this, the order of reactivity suggests that aryl halides having electron withdrawing groups stabilize the transition state which corresponds to good yields with a short reaction time in comparison to aryl halides having electron donating groups (Figure 2).

[1860-5397-6-35-2]
Figure 2: Proposed reaction pathway for the CuO-nanoparticles catalyzed C–C coupling reaction.

The reaction was then carried out with recycled catalyst. The CuO-nanoparticles were recovered by centrifugation of the reaction mixture and washed thoroughly with ethyl acetate. The resulting nanoparticles could be reused for several cycles without any significant loss of activity. In our study, we used same nanoparticles three times and the results are summarized below (Table 5). The TEM and XRD analysis of recycled CuO-nanoparticles, after the fourth run showed that particles are identical in shape and size, hence CuO-nanoparticles are unchanged during the reaction (Figure 3).

Table 5: Recycle studies of nano-CuO for C-arylation reactiona.
RunTime (h)Yieldb (%)
1880
2878
3877
4876
[1860-5397-6-35-3]
Figure 3: Powder X-ray diffraction pattern and TEM image of recycled CuO-nanoparticles.
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Conclusion

An efficient, facile and economical method for synthesis of 3-arylpentane-2,4-diones (Table 3) and diethyl 2-aryl-malonates (Table 4) has been developed using CuO-nanoparticles as the catalyst. The products were obtained in moderate to good yields and the catalyst can be recycled up to four cycles with almost consistent activity. The present protocol represents a simple and remarkably active catalytic system to catalyze Ullmann-type C–C bond formation, which potentially offers an efficient protocol for accessing a variety of α-arylated dicarbonyl compounds.

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Experimental

General

The materials were purchased from Sigma-Aldrich and Merck and were used without further purification. Mass spectra were recorded in a TOF-mass spectrometer model no. KC455. 1H NMR and 13C NMR spectra were recorded on a Bruker spectrospin at 300 MHz and 75 MHz, respectively. All 1H NMR and 13C NMR spectra were run in CDCl3 and chemical shifts are expressed as ppm relative to internal Me4Si. Elemental analyses were performed using Heraeus CHN-Rapid Analyzer. Powder X-ray diffraction measurements were carried out on a Bruker D8 Discover HR-XRD instrument using Cu Kα radiation (λ = 1.54184 Å).

Experimental Section

CuO-nanoparticles (10 mol %) were added to the mixture of iodobenzene (1 mmol), acetylactone (3 mmol) and (0.5 mmol) of Cs2CO3 in DMSO (2 ml) under nitrogen atmosphere. The resulting reaction mixture was stirred at 80 °C for 8 h. Progress of the reaction was continuously monitored by TLC. After completion of reaction, the catalyst was recovered by centrifugation. The nanoparticles, were first washed with distilled methanol to remove some of the Cs2CO3, then several times with ethyl acetate and dried in an oven overnight at 150 °C. The filtrate was poured into 1N HCl and extracted with EtOAc. The combined organic layers were washed with brine, dried over anhydrous Na2SO4 and concentrated at reduced pressure. The residue was chromatographed to afford pure 3-phenyl-2,4-pentadione (Entry 1, Table 3). From the spectral data it was observed that some products show 1,3-keto-enol tautomerism. The structures of all the products were unambiguously established on the basis of their spectral properties (1H NMR, MS and 13C NMR).

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Supporting Information

Supporting Information File 1: Typical procedure and characterization data of prepared compounds
Format: PDF   Size: 41.7 KB   Download

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Acknowledgements

Saurav Bhardwaj and Roona Poddar thank CSIR, New Delhi for providing a fellowship.

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Top
Figure 1: Powder X-ray diffraction pattern and TEM image of nano CuO (fresh). Move  Close
Figure 2: Proposed reaction pathway for the CuO-nanoparticles catalyzed C–C coupling reaction. Move  Close
Figure 3: Powder X-ray diffraction pattern and TEM image of recycled CuO-nanoparticles. Move  Close
Scheme 1: Synthesis of 3-phenylpentane-2,4-dione using CuO-nanoparticles. Move  Close
Scheme 2: Synthesis of 3-phenylpentane-2,4-dione using CuO-nanoparticles. Move  Close
Scheme 3: Synthesis of diethyl 2-aryl-malonate using CuO-nanoparticles. Move  Close
Table 1: C-arylation reaction catalyzed by different Cu catalystsa. Move  Close
EntryCatalystTime (h)Yieldb (%)
1Cu(OAc)21020
2Cu-np1010
3CuO1024
4CuO-np880
Table 2: CuO-nanoparticles catalyzed coupling reaction of acetylacetone and iodobenzene in various solventsa. Move  Close
EntrySolventTime (h)Yieldb (%)
1DMSO880
2Toluene158
3THF1512
4Acetonitrile1532
Table 3: C-arylation of acetylacetone using different aryl halidesa Move  Close
EntryAryl halideProductTime (h)Yieldb (%)
1iodobenzene3-phenylpentane-2,4-dione880
2bromobenzene3-phenylpentane-2,4-dione1079
3p-nitroiodobenzene3-(4-nitrophenyl)-pentane-2,4-dione683
4p-methyliodobenzene3-p-tolylpentane-2,4-dione1078
5m-trifluoromethyliodobenzene3-(3-trifluromethyl-phenyl)-pentane-2,4-dione781
61-iodo-2-methylbenzene3-o-tolyl-pentane-2,4-dione1176
71-iodo-4-methoxybenzene3-(4-methoxy-phenyl)-pentane-2,4-dione1275
Table 4: C-arylation of diethyl malonate using different aryl halidesa. Move  Close
EntryAryl halideProductTime (h)Yieldb (%)
1iodobenzene2-phenylmalonic acid diethylester978
2bromobenzene2-phenylmalonic acid diethylester1176
3p-nitroiodobenzene2-(4-nitrophenyl)-malonic acid diethylester681
4p-methyliodobenzene2-p-tolylmalonic acid diethylester1276
5m-trifluoromethyliodobenzene2-(3-trifluromethyl-phenyl)-malonic acid diethylester780
61-iodo-2-methylbenzene2-o-tolylmalonic acid diethylester1375
71-iodo-4-methoxybenzene3-(4-methoxy-phenyl)-malonic acid diethylether1474
Table 5: Recycle studies of nano-CuO for C-arylation reactiona. Move  Close
RunTime (h)Yieldb (%)
1880
2878
3877
4876
19.Li, P.; Wang, L.; Li, H. Tetrahedron 2005, 61, 8633–8640. doi:10.1016/j.tet.2005.07.013
Go to reference 19
20.Okuro, K.; Furuune, M.; Miura, M.; Nomura, M. J. Org. Chem. 1993, 58, 7606–7607. doi:10.1021/jo00078a053
Go to reference 20
15.Jiang, Y.; Wu, N.; Wu, H.; He, M. Synlett 2005, 2731–2734. doi:10.1055/s-2005-918921
16.Yip, S. F.; Cheung, H. Y.; Zhou, Z.; Kwong, F. Y. Org. Lett. 2007, 9, 3469–3472. doi:10.1021/ol701473p
Go to references 15,16
17.Fox, J. M.; Huang, X.; Chieffi, A.; Buchwald, S. L. J. Am. Chem. Soc. 2000, 122, 1360–1370. doi:10.1021/ja993912d
18.Culkin, D. A.; Hartwig, J. F. J. Am. Chem. Soc. 2001, 123, 5816–5817. doi:10.1021/ja015732l
Go to references 17,18
12.Thathagar, M. B.; Beckers, J.; Rothenberg, G. Green Chem. 2004, 6, 215–218. doi:10.1039/b401586j
13.Suzuki, H.; Kobayashi, T.; Osuka, A. Chem. Lett. 1983, 12, 589–590. doi:10.1246/cl.1983.589
Go to references 12,13
14.Setsune, J.-I.; Matsukawa, K.; Wakemoto, H.; Kitao, T. Chem. Lett. 1981, 10, 367–370. doi:10.1246/cl.1981.367
Go to reference 14
4.Ramthoul, Y. K.; Chartrand, A. Org. Lett. 2007, 9, 1029–1032. doi:10.1021/ol063057k
5.Masselot, D.; Charmant, J. P. H.; Gallagher, T. J. Am. Chem. Soc. 2006, 128, 694–695. doi:10.1021/ja056964d
6.Wu, J. Y.; Nie, L.; Luo, J.; Dai, W.-M. Synlett 2007, 2728–2732. doi:10.1055/s-2007-991053
7.Kamikawa, K.; Takemoto, I.; Takemoto, S.; Matsuzaka, H. J. Org. Chem. 2007, 72, 7406–7408. doi:10.1021/jo0711586
Go to references 4-7
8.Wright, J. B. J. Org. Chem. 1964, 29, 1905–1909. doi:10.1021/jo01030a059
9.Beare, N. A.; Hartwig, J. F. J. Org. Chem. 2002, 67, 541–555. doi:10.1021/jo016226h
10.You, J.; Verkade, J. G. Angew. Chem. 2003, 42, 5051–5053. doi:10.1002/anie.200351954
11.Thathagar, M. B.; Rothenberg, G. Org. Biomol. Chem. 2006, 4, 111–115. doi:10.1039/b513450a
Go to references 8-11
1.Ren, T. Chem. Rev. 2008, 108, 4185–4207. doi:10.1021/cr8002592
2.Hart, D. J. Science 1984, 223, 883–887. doi:10.1126/science.223.4639.883
3.Iwama, T.; Rawal, V. H. Org. Lett. 2006, 8, 5725–5728. doi:10.1021/ol062093g
Go to references 1-3
29.Kidwai, M.; Poddar, R.; Mothsra, P. Beil. J. Org. Chem. 2009, 5, No. 10. doi:10.3762/bjoc.5.10
30.Kidwai, M.; Poddar, R.; Diwaniyan, S.; Kuhad, R. C. Adv. Synth. Catal. 2009, 351, 589–595. doi:10.1002/adsc.200800611
Go to references 29,30
31.Kidwai, M.; Bhatnagar, D.; Mishra, N. K.; Bansal, V. Catal. Commun. 2008, 9, 2547–2549. doi:10.1016/j.catcom.2008.07.010
32.Kidwai, M.; Bhardwaj, S.; Mishra, N. K.; Bansal, V.; Kumar, A.; Mozumdar, S. Catal. Commun. 2009, 10, 1514–1517. doi:10.1016/j.catcom.2009.04.006
33.Kidwai, M.; Bansal, V.; Kumar, A.; Mozumdar, S. Green Chem. 2007, 9, 742–745. doi:10.1039/b702287e
Go to references 31-33
34.Kidwai, M.; Mishra, N. K.; Bansal, V.; Kumar, A.; Mozumdar, S. Tetrahedron Lett. 2007, 48, 8883–8887. doi:10.1016/j.tetlet.2007.10.050
35.Gonzalez-Arellano, C.; Luque, G.; Macquarrie, D. J. Chem. Commun. 2009, 1410–1412. doi:10.1039/b818767c
Go to references 34,35
21.Lucas, E.; Decker, S.; Khaleel, A.; Seitz, A.; Fultz, S.; Ponce, A.; Li, W.; Carnes, C.; Klabunde, K. J. Chem.–Eur. J. 2001, 7, 2505–2510. doi:10.1002/1521-3765(20010618)7:12<2505::AID-CHEM25050>3.0.CO;2-R
Go to reference 21
22.Jiang, Y.; Decker, S.; Mohs, C.; Klabunde, K. J. J. Catal. 1998, 180, 24–35. doi:10.1006/jcat.1998.2257
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