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Efficient N-arylation of amines catalyzed by Cu–Fe–hydrotalcite
Catalysis Communications 8 (2007) 65–68 www.elsevier.com/locate/catcom
Efficient N-arylation of amines catalyzed by Cu–Fe–hydrotalcite Vinod H. Jadhav, Deepa K. Dumbre, Vilas B. Phapale, Hanumant B. Borate, Radhika D. Wakharkar * Division of Organic Chemistry Technology, National Chemical Laboratory, Dr. Homi Bhabha Road, Pune 411 008, Maharashtra, India Received 12 April 2006; received in revised form 15 May 2006; accepted 15 May 2006 Available online 2 June 2006
Abstract An efficient N-arylation of amines with aryl halides in presence of heterogeneous recyclable Cu–Fe–hydrotalcite catalyst has been developed. Ó 2006 Elsevier B.V. All rights reserved. Keywords: N-arylation; Amines; Aryl halides; Cu–Fe–hydrotalcite; Heterogeneous catalyst
1. Introduction N-arylation of various amines and amides has continued to attract synthetic chemists as the N-arylated products constitute the subunits of many biologically active molecules [1]. The different methods reported [2] for N-arylation include coupling of amines or isocyanates with aryl boronic acids, aryl halides, aryl triflates, etc. using copper, cuprous iodide, cupric acetate, copper-diamine complexes, palladium, cobalt, or nickel catalysts. Cu-catalyzed Ullmann coupling protocols and Ullmann type processes for C–N bond formation have been reported [2e] and amination of aryl iodides using various ligands has been extensively studied. Application of ionic liquids [3] or microwave [4] for N-arylation has been reported recently. Some of these methods involve use of expensive chemicals, tedious work up or sensitive catalysts/ligands, therefore it has been recognized that developing clean N-arylation is one of the most important challenges in green chemistry. The use of heterogeneous catalysts offers the advantages such as ease of work up, recyclability and development of environmentally benign synthetic procedures. Solid supports like KF/ Al2O3 have been used for N-arylation in recent years [5].
*
Corresponding author. Tel.: +91 20 25902284; fax: +91 20 25902629. E-mail address: [email protected] (R.D. Wakharkar).
1566-7367/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.catcom.2006.05.030
In continuation of our research interest in the use of heterogeneous catalysts for organic transformations recently, we synthesized a double-layered hydrotalcite catalyst containing Cu–Fe from their corresponding nitrites, potassium hydroxide, and potassium carbonate. The catalyst contained not only HT phase but also mixed metal hydroxide/carbonate phases. Considering the requirement of basic conditions and the role of copper in such Ullmanntype C–N bond forming reactions we employed Cu–Fe– hydrotalcite for N-arylation of amines with aryl halides (Scheme 1). Cu–Fe–hydrotalcite was found to be capable of catalyzing this reaction efficiently and this environmentally friendly way for the synthesis of N-aryl-amines has been communicated herein. 2. Experimental All reactions were monitored by TLC. IR spectra were recorded on an ATI MATTSON RS-1 FT-IR spectrometer and 1H NMR spectra on a Bruker AC-200 spectrometer. 2.1. Preparation of catalyst The layered double hydroxide (LDH) and/or mixed hydroxides containing Cu(II) and Fe(III) with Cu(II)/ Fe(III) mole ratio of 3:1 (Cu–Fe–HT) was prepared by adding two aqueous solutions simultaneously, one
66
V.H. Jadhav et al. / Catalysis Communications 8 (2007) 65–68 X
R-NHR' +
R''
Cu-Fe-hydrotalcite, toluene, reflux
NRR' R''
R-NHR'=Substituted aniline, indole, cyclohexyl amine, benzyl amine X=Br, I R''=H, OMe, NO2, Cl, CHO
Scheme 1.
containing copper nitrate (38.60 g, 159.8 mmol) and ferric nitrate (21.57 g, 53.4 mmol) in deionized water (200 ml) with the required Cu/Fe ratio and second containing potassium hydroxide (30.38 g, 541.4 mmol) and potassium carbonate (5.52 g, 39.9 mmol) in deionized water (600 ml), dropwise into a flask under vigorous stirring at 40 °C, while maintaining a constant pH of 11–12. The resulting gel-like material was aged for 0.5 h, filtered, thoroughly washed with deionized water and dried at 80 °C in vacuum oven and then further heated in air oven at 200 °C for 12 h. 2.2. Typical procedure for preparation of (4-methoxyphenyl)phenylamine To a solution of aniline (0.5 g, 5.3 mmol) and 4-bromoanisole (1.0 g, 5.3 mmol) in toluene (7 mL) was added Cu– Fe–hydrotalcite (50 mg, 10% by wt of amine). The reaction mixture was stirred under reflux at 130 °C for 15 h (monitored by TLC). It was then cooled to RT, filtered, washed with toluene (10 mL) and concentrated under reduced pressure. The crude product obtained was purified by column chromatography over silica gel to afford the (4-methoxyphenyl)-phenylamine (0.85 g, 80%); IR (chloroform): m 3411, 3018, 1611, 1513, 1489, 1443 cm 1; 1H NMR (200 MHz, CDCl3 + CCl4): d 3.69 (s, 3H), 6.59 (d, J = 8 Hz, 2H), 7.40–7.55 (m, 5H), 7.85 (d, J = 8 Hz, 3H, including N–H); 13C NMR (50 MHz, CDCl3 + CCl4): d 55.2, 112.7, 115.6 (2C), 122.8 (2C), 128.9 (2C), 130.9, 132.1 (2C), 152.5, 158.6; Anal. Calc. for C13H13NO: C, 78.39%; H, 6.53%; N, 7.03%. Found: C, 78.25%; H, 6.48%; N, 7.00%. 3. Results and discussion The importance of N-aryl-amines and the advantages of heterogeneous catalysis prompted us to explore the possibility of arylation of various amines by reaction with aryl halides in the presence of Cu–Fe–hydrotalcite. The layered double hydroxide (LDH) and/or mixed hydroxides containing Cu(II) and Fe(III) with Cu(II)/ Fe(III) mole ratio of 3:1 (Cu–Fe–HT) was prepared by a known procedure [6], by adding two aqueous solutions simultaneously, one containing mixed nitrates of the divalent and trivalent metals (Cu/Fe) and second containing
potassium hydroxide and potassium carbonate in deionized water, dropwise into a flask under vigorous stirring at 40 °C, while maintaining a constant pH of 11–12. The resulting gel-like material was aged for 0.5 h, filtered, thoroughly washed with deionized water and dried at 80 °C in vacuum oven and then further heated in air oven at 200 °C for 12 h. The catalyst was characterized for the crystalline phase(s) and spacing between hydroxide layers (d(0 0 1) spacing) by XRD (using a Phillips Diffractometer (1730 series) and Cu Ka radiations). The catalyst contained not only HT phase but also mixed HT and metal hydroxide/ carbonate phases. Before carrying out the surface area measurements, the catalyst (0.1–0.5 g) was pretreated in situ in an U-shaped sample cell in a flow of moisture-free N2–He (1:3) gas mixture (30 cm3 g 1) at 200 °C for 2 h. The surface area measurement was carried out by the single point N2 adsorption method (using a Surface Area Analyser; Quanta Chrome, USA) and the observed surface area was 65.9 m2 g 1. Also for measuring the pH of the suspension in water, 0.15 g catalyst was suspended in 10 ml deionized water at room temperature and the observed pH was 7.43. The CO23 content of the catalyst (by treating the catalyst with 4.0 M HNO3 and measuring quantitatively the CO2 evolved) was observed to be 0.286 mmol g 1. Initially, aniline was reacted with one equivalent of 4-bromo-anisole in toluene at room temperature in presence of Cu–Fe–hydrotalcite (10% by weight of aniline) when there was no reaction. Increase in temperature helped the reaction to occur and it was gratifying that the desired product was obtained in 80% yield when the reaction mixture was refluxed for 15 h. Absence of product in a similar reaction without catalyst confirmed the role of the catalyst. When aniline was reacted with 4-iodoanisole, 85% product was obtained in 12 h. A number of amines were reacted with different aryl halides to study the scope and limitations of the reaction and the results are shown in Table 1. When the catalyst used in the reaction (entry no. 1), was reused, the product yield in the second and third reuse of the catalyst for the same reaction was 79% and 77%, respectively. This newly developed Cu–Fe–hydrotalcite catalyzed N-arylation protocol was applied to substituted anilines like 2-methoxy-aniline, 4-methoxy-2-nitroaniline and indole, cyclohexyl amine and benzyl amine which were reacted with 4-bromo-anisole to afford the corresponding products in 74–87% yields. Bromobenzene, iodobenzene, 4-bromo-chloro-benzene, and 4-bromo-benzaldehyde were used as the variants on aryl halide side and it was observed that they efficiently transformed to the corresponding products in excellent yield. To our surprise when 4bromo-benzaldehyde was subjected to this transformation with aniline no traces of Schiffs base product was observed and the reaction was highly selective for the desired transformation. It is noteworthy that the reaction was selective for primary amines and did not yield further arylation to give triarylamines. Diarylamine was separately treated with iodoanisole to confirm this observation when the starting
V.H. Jadhav et al. / Catalysis Communications 8 (2007) 65–68
67
Table 1 N-arylation of amines catalyzed by Cu–Fe–hydrotalcite Ent. No.
Amine
Halide
1
Aniline
4-Bromo-anisole
2
Aniline
4-Iodoanisole
3
Aniline
Bromobenzene
4
Aniline
Iodobenzene
5
2-Methoxy-aniline
4-Bromo-anisole
Product
2-Methoxy-aniline
OMe
15
80
N H
OMe
12
82
14
79
12
81
12
76
12
75
16
77
16
74
12
85
12
87
12
81
12
80
12
79
12
81
12
76
12
79
N H N H
OMe
Bromobenzene
% Yield
N H
OMe
N H
6
Time in h
OMe N H
7
4-Methoxy-2-nitroaniline
Bromobenzene
NO 2 MeO
8
4-Methoxy-2-nitroaniline
N H
4-Bromo-anisole
NO2 MeO
9
Indole
Bromobenzene
10
Indole
4-Bromo-anisole
11
Cyclohexylamine
Bromobenzene
12
Cyclohexylamine
4-Bromo-anisole
13
Benzylamine
Bromobenzene
N H
OMe
N
N
OMe
N H
OMe
N H
N H
14
Benzylamine
4-Bromo-anisole
15
Aniline
4-Bromo-chloro-benzene
16
Aniline
4-Bromo-benzaldehyde
materials remained unchanged. Although this catalyst worked well with primary amines and indole when other heterocycles such as imidazole, triazole, benzimidazole, and substituted indole derivatives were employed as substrates, the reaction did not proceed to give the expected products which indicated the high selectivity of the catalyst towards primary amines. When the Cu–Al hydrotalcite and Mg–Fe–hydrotalcite catalysts [7] were used instead of the Cu–Fe–hydrotalcite, the yield of (4-methoxyphenyl)-phenyl amine in the reaction between aniline and 4-bromo-anisole in 15 h was 25% and 10%, respectively. The presence of Cu and Fe in the Cu–Fe–hydrotalcite seems to have synergetic effect on the C–N coupling reaction.
N H
OMe
N H
Cl
N H
CHO
4. Conclusion We have developed an efficient useful greener method for N-arylation of amines by reaction of different amines with aryl halides in presence of Cu–Fe–hydrotalcite. The reaction conditions are mild and various functional groups are tolerated. In comparison with reported protocols this method avoids the use of difficult to separate and expensive catalysts and ligands, excess of amines or use of base and instead employs a heterogeneous catalyst that is easily removed from the product simply by filtration and can be recycled/reused. Selective N-arylation of primary amines is possible in case of amino benzaldehyde without formation of Schiffs base.
68
V.H. Jadhav et al. / Catalysis Communications 8 (2007) 65–68
Acknowledgement V.H.J. thanks Lady Tata Memorial Trust, Mumbai for Junior Research Fellowship. References [1] (a) S., Alexander, W.K., Geoffery, G., Zheng, Eur. Pat. Appl. E.P. 13144 (9 July 1980), 96pp; (b) E. Moshe, Eur. J. Med. Chem. Chim. Ther. 16 (1981) 199–206. [2] (a) D.T. Chan, K.L. Monaco, R.-U. Wang, M.P. Winters, Tetrahedron Lett. 39 (1998) 2933–2936; (b) P.Y.S. Lam, C.G. Clark, S. Saubern, J. Adams, M.P. Winters, D.M.T. Chan, A. Combs, Tetrahedron Lett. 39 (1998) 2941–2944;
[3] [4] [5] [6] [7]
(c) J.P. Collman, M. Zhong, Org. Lett. 2 (2000) 1233–1236; (d) W.W.K.R. Mederski, M. Lefort, M. Germann, D. Kux, Tetrahedron 55 (1999) 12757–12770; (e) F.Y. Kwong, S.L. Buchwald, Org. Lett. 5 (2003) 793–796, and references cited therein; (f) B. Sezen, D. Sames, J. Am. Chem. Soc. 125 (2003) 5274–5275; (g) A. Kuwahara, K. Nakano, K. Nozaki, J. Org. Chem. 70 (2005) 413–419. F.Y. Wang, Z.C. Chen, Q.G. Zheng, J. Chem. Res. 3 (2004) 206–207. P. Das, B. Basu, Syn. Commun. 34 (2004) 2177–2184. W.J. Smith, J.S. Sawyer, Tetrahedron Lett. 37 (1996) 299–302. V.R. Choudhary, D.K. Dumbre, B.S. Uphade, V.S. Narkhede, J. Mol. Catal. A 215 (2004) 129–135. V.R. Choudhary, P.A. Choudhary, V.S. Narkhede, Catal. Commun. 4 (2003) 171.
Efficient N-arylation of amines catalyzed by Cu–Fe–hydrotalcite Vinod H. Jadhav, Deepa K. Dumbre, Vilas B. Phapale, Hanumant B. Borate, Radhika D. Wakharkar * Division of Organic Chemistry Technology, National Chemical Laboratory, Dr. Homi Bhabha Road, Pune 411 008, Maharashtra, India Received 12 April 2006; received in revised form 15 May 2006; accepted 15 May 2006 Available online 2 June 2006
Abstract An efficient N-arylation of amines with aryl halides in presence of heterogeneous recyclable Cu–Fe–hydrotalcite catalyst has been developed. Ó 2006 Elsevier B.V. All rights reserved. Keywords: N-arylation; Amines; Aryl halides; Cu–Fe–hydrotalcite; Heterogeneous catalyst
1. Introduction N-arylation of various amines and amides has continued to attract synthetic chemists as the N-arylated products constitute the subunits of many biologically active molecules [1]. The different methods reported [2] for N-arylation include coupling of amines or isocyanates with aryl boronic acids, aryl halides, aryl triflates, etc. using copper, cuprous iodide, cupric acetate, copper-diamine complexes, palladium, cobalt, or nickel catalysts. Cu-catalyzed Ullmann coupling protocols and Ullmann type processes for C–N bond formation have been reported [2e] and amination of aryl iodides using various ligands has been extensively studied. Application of ionic liquids [3] or microwave [4] for N-arylation has been reported recently. Some of these methods involve use of expensive chemicals, tedious work up or sensitive catalysts/ligands, therefore it has been recognized that developing clean N-arylation is one of the most important challenges in green chemistry. The use of heterogeneous catalysts offers the advantages such as ease of work up, recyclability and development of environmentally benign synthetic procedures. Solid supports like KF/ Al2O3 have been used for N-arylation in recent years [5].
*
Corresponding author. Tel.: +91 20 25902284; fax: +91 20 25902629. E-mail address: [email protected] (R.D. Wakharkar).
1566-7367/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.catcom.2006.05.030
In continuation of our research interest in the use of heterogeneous catalysts for organic transformations recently, we synthesized a double-layered hydrotalcite catalyst containing Cu–Fe from their corresponding nitrites, potassium hydroxide, and potassium carbonate. The catalyst contained not only HT phase but also mixed metal hydroxide/carbonate phases. Considering the requirement of basic conditions and the role of copper in such Ullmanntype C–N bond forming reactions we employed Cu–Fe– hydrotalcite for N-arylation of amines with aryl halides (Scheme 1). Cu–Fe–hydrotalcite was found to be capable of catalyzing this reaction efficiently and this environmentally friendly way for the synthesis of N-aryl-amines has been communicated herein. 2. Experimental All reactions were monitored by TLC. IR spectra were recorded on an ATI MATTSON RS-1 FT-IR spectrometer and 1H NMR spectra on a Bruker AC-200 spectrometer. 2.1. Preparation of catalyst The layered double hydroxide (LDH) and/or mixed hydroxides containing Cu(II) and Fe(III) with Cu(II)/ Fe(III) mole ratio of 3:1 (Cu–Fe–HT) was prepared by adding two aqueous solutions simultaneously, one
66
V.H. Jadhav et al. / Catalysis Communications 8 (2007) 65–68 X
R-NHR' +
R''
Cu-Fe-hydrotalcite, toluene, reflux
NRR' R''
R-NHR'=Substituted aniline, indole, cyclohexyl amine, benzyl amine X=Br, I R''=H, OMe, NO2, Cl, CHO
Scheme 1.
containing copper nitrate (38.60 g, 159.8 mmol) and ferric nitrate (21.57 g, 53.4 mmol) in deionized water (200 ml) with the required Cu/Fe ratio and second containing potassium hydroxide (30.38 g, 541.4 mmol) and potassium carbonate (5.52 g, 39.9 mmol) in deionized water (600 ml), dropwise into a flask under vigorous stirring at 40 °C, while maintaining a constant pH of 11–12. The resulting gel-like material was aged for 0.5 h, filtered, thoroughly washed with deionized water and dried at 80 °C in vacuum oven and then further heated in air oven at 200 °C for 12 h. 2.2. Typical procedure for preparation of (4-methoxyphenyl)phenylamine To a solution of aniline (0.5 g, 5.3 mmol) and 4-bromoanisole (1.0 g, 5.3 mmol) in toluene (7 mL) was added Cu– Fe–hydrotalcite (50 mg, 10% by wt of amine). The reaction mixture was stirred under reflux at 130 °C for 15 h (monitored by TLC). It was then cooled to RT, filtered, washed with toluene (10 mL) and concentrated under reduced pressure. The crude product obtained was purified by column chromatography over silica gel to afford the (4-methoxyphenyl)-phenylamine (0.85 g, 80%); IR (chloroform): m 3411, 3018, 1611, 1513, 1489, 1443 cm 1; 1H NMR (200 MHz, CDCl3 + CCl4): d 3.69 (s, 3H), 6.59 (d, J = 8 Hz, 2H), 7.40–7.55 (m, 5H), 7.85 (d, J = 8 Hz, 3H, including N–H); 13C NMR (50 MHz, CDCl3 + CCl4): d 55.2, 112.7, 115.6 (2C), 122.8 (2C), 128.9 (2C), 130.9, 132.1 (2C), 152.5, 158.6; Anal. Calc. for C13H13NO: C, 78.39%; H, 6.53%; N, 7.03%. Found: C, 78.25%; H, 6.48%; N, 7.00%. 3. Results and discussion The importance of N-aryl-amines and the advantages of heterogeneous catalysis prompted us to explore the possibility of arylation of various amines by reaction with aryl halides in the presence of Cu–Fe–hydrotalcite. The layered double hydroxide (LDH) and/or mixed hydroxides containing Cu(II) and Fe(III) with Cu(II)/ Fe(III) mole ratio of 3:1 (Cu–Fe–HT) was prepared by a known procedure [6], by adding two aqueous solutions simultaneously, one containing mixed nitrates of the divalent and trivalent metals (Cu/Fe) and second containing
potassium hydroxide and potassium carbonate in deionized water, dropwise into a flask under vigorous stirring at 40 °C, while maintaining a constant pH of 11–12. The resulting gel-like material was aged for 0.5 h, filtered, thoroughly washed with deionized water and dried at 80 °C in vacuum oven and then further heated in air oven at 200 °C for 12 h. The catalyst was characterized for the crystalline phase(s) and spacing between hydroxide layers (d(0 0 1) spacing) by XRD (using a Phillips Diffractometer (1730 series) and Cu Ka radiations). The catalyst contained not only HT phase but also mixed HT and metal hydroxide/ carbonate phases. Before carrying out the surface area measurements, the catalyst (0.1–0.5 g) was pretreated in situ in an U-shaped sample cell in a flow of moisture-free N2–He (1:3) gas mixture (30 cm3 g 1) at 200 °C for 2 h. The surface area measurement was carried out by the single point N2 adsorption method (using a Surface Area Analyser; Quanta Chrome, USA) and the observed surface area was 65.9 m2 g 1. Also for measuring the pH of the suspension in water, 0.15 g catalyst was suspended in 10 ml deionized water at room temperature and the observed pH was 7.43. The CO23 content of the catalyst (by treating the catalyst with 4.0 M HNO3 and measuring quantitatively the CO2 evolved) was observed to be 0.286 mmol g 1. Initially, aniline was reacted with one equivalent of 4-bromo-anisole in toluene at room temperature in presence of Cu–Fe–hydrotalcite (10% by weight of aniline) when there was no reaction. Increase in temperature helped the reaction to occur and it was gratifying that the desired product was obtained in 80% yield when the reaction mixture was refluxed for 15 h. Absence of product in a similar reaction without catalyst confirmed the role of the catalyst. When aniline was reacted with 4-iodoanisole, 85% product was obtained in 12 h. A number of amines were reacted with different aryl halides to study the scope and limitations of the reaction and the results are shown in Table 1. When the catalyst used in the reaction (entry no. 1), was reused, the product yield in the second and third reuse of the catalyst for the same reaction was 79% and 77%, respectively. This newly developed Cu–Fe–hydrotalcite catalyzed N-arylation protocol was applied to substituted anilines like 2-methoxy-aniline, 4-methoxy-2-nitroaniline and indole, cyclohexyl amine and benzyl amine which were reacted with 4-bromo-anisole to afford the corresponding products in 74–87% yields. Bromobenzene, iodobenzene, 4-bromo-chloro-benzene, and 4-bromo-benzaldehyde were used as the variants on aryl halide side and it was observed that they efficiently transformed to the corresponding products in excellent yield. To our surprise when 4bromo-benzaldehyde was subjected to this transformation with aniline no traces of Schiffs base product was observed and the reaction was highly selective for the desired transformation. It is noteworthy that the reaction was selective for primary amines and did not yield further arylation to give triarylamines. Diarylamine was separately treated with iodoanisole to confirm this observation when the starting
V.H. Jadhav et al. / Catalysis Communications 8 (2007) 65–68
67
Table 1 N-arylation of amines catalyzed by Cu–Fe–hydrotalcite Ent. No.
Amine
Halide
1
Aniline
4-Bromo-anisole
2
Aniline
4-Iodoanisole
3
Aniline
Bromobenzene
4
Aniline
Iodobenzene
5
2-Methoxy-aniline
4-Bromo-anisole
Product
2-Methoxy-aniline
OMe
15
80
N H
OMe
12
82
14
79
12
81
12
76
12
75
16
77
16
74
12
85
12
87
12
81
12
80
12
79
12
81
12
76
12
79
N H N H
OMe
Bromobenzene
% Yield
N H
OMe
N H
6
Time in h
OMe N H
7
4-Methoxy-2-nitroaniline
Bromobenzene
NO 2 MeO
8
4-Methoxy-2-nitroaniline
N H
4-Bromo-anisole
NO2 MeO
9
Indole
Bromobenzene
10
Indole
4-Bromo-anisole
11
Cyclohexylamine
Bromobenzene
12
Cyclohexylamine
4-Bromo-anisole
13
Benzylamine
Bromobenzene
N H
OMe
N
N
OMe
N H
OMe
N H
N H
14
Benzylamine
4-Bromo-anisole
15
Aniline
4-Bromo-chloro-benzene
16
Aniline
4-Bromo-benzaldehyde
materials remained unchanged. Although this catalyst worked well with primary amines and indole when other heterocycles such as imidazole, triazole, benzimidazole, and substituted indole derivatives were employed as substrates, the reaction did not proceed to give the expected products which indicated the high selectivity of the catalyst towards primary amines. When the Cu–Al hydrotalcite and Mg–Fe–hydrotalcite catalysts [7] were used instead of the Cu–Fe–hydrotalcite, the yield of (4-methoxyphenyl)-phenyl amine in the reaction between aniline and 4-bromo-anisole in 15 h was 25% and 10%, respectively. The presence of Cu and Fe in the Cu–Fe–hydrotalcite seems to have synergetic effect on the C–N coupling reaction.
N H
OMe
N H
Cl
N H
CHO
4. Conclusion We have developed an efficient useful greener method for N-arylation of amines by reaction of different amines with aryl halides in presence of Cu–Fe–hydrotalcite. The reaction conditions are mild and various functional groups are tolerated. In comparison with reported protocols this method avoids the use of difficult to separate and expensive catalysts and ligands, excess of amines or use of base and instead employs a heterogeneous catalyst that is easily removed from the product simply by filtration and can be recycled/reused. Selective N-arylation of primary amines is possible in case of amino benzaldehyde without formation of Schiffs base.
68
V.H. Jadhav et al. / Catalysis Communications 8 (2007) 65–68
Acknowledgement V.H.J. thanks Lady Tata Memorial Trust, Mumbai for Junior Research Fellowship. References [1] (a) S., Alexander, W.K., Geoffery, G., Zheng, Eur. Pat. Appl. E.P. 13144 (9 July 1980), 96pp; (b) E. Moshe, Eur. J. Med. Chem. Chim. Ther. 16 (1981) 199–206. [2] (a) D.T. Chan, K.L. Monaco, R.-U. Wang, M.P. Winters, Tetrahedron Lett. 39 (1998) 2933–2936; (b) P.Y.S. Lam, C.G. Clark, S. Saubern, J. Adams, M.P. Winters, D.M.T. Chan, A. Combs, Tetrahedron Lett. 39 (1998) 2941–2944;
[3] [4] [5] [6] [7]
(c) J.P. Collman, M. Zhong, Org. Lett. 2 (2000) 1233–1236; (d) W.W.K.R. Mederski, M. Lefort, M. Germann, D. Kux, Tetrahedron 55 (1999) 12757–12770; (e) F.Y. Kwong, S.L. Buchwald, Org. Lett. 5 (2003) 793–796, and references cited therein; (f) B. Sezen, D. Sames, J. Am. Chem. Soc. 125 (2003) 5274–5275; (g) A. Kuwahara, K. Nakano, K. Nozaki, J. Org. Chem. 70 (2005) 413–419. F.Y. Wang, Z.C. Chen, Q.G. Zheng, J. Chem. Res. 3 (2004) 206–207. P. Das, B. Basu, Syn. Commun. 34 (2004) 2177–2184. W.J. Smith, J.S. Sawyer, Tetrahedron Lett. 37 (1996) 299–302. V.R. Choudhary, D.K. Dumbre, B.S. Uphade, V.S. Narkhede, J. Mol. Catal. A 215 (2004) 129–135. V.R. Choudhary, P.A. Choudhary, V.S. Narkhede, Catal. Commun. 4 (2003) 171.