Palladium-catalyzed efficient Suzuki–Miyaura reaction of potassium aryltrifluoroborates in water

Catalysis Communications 69 (2015) 81–85

Contents lists available at ScienceDirect

Catalysis Communications journal homepage: www.elsevier.com/locate/catcom

Short communication

Palladium-catalyzed efficient Suzuki–Miyaura reaction of potassium aryltrifluoroborates in water Chun Liu ⁎, Xinmin Li, Xinnan Wang, Zilin Jin State Key Laboratory of Fine Chemicals, Dalian University of Technology, Linggong Road 2, 116024 Dalian, China

a r t i c l e

i n f o

Article history: Received 17 April 2015 Received in revised form 26 May 2015 Accepted 29 May 2015 Available online 3 June 2015 Keywords: Palladium Suzuki–Miyaura reaction Aryltrifluoroborates Water Gram scale

a b s t r a c t An efficient and environment-friendly protocol has been developed for the palladium-catalyzed Suzuki–Miyaura reaction of potassium aryltrifluoroborates with (hetero)aryl halides in water without any additive. This method allows the preparation of a variety of biaryls and heterobiaryls in excellent yields. In addition, the cross-coupling product can be isolated in good yields and high purity by simple filtration and recrystallization as the reaction was performed on gram scale. © 2015 Elsevier B.V. All rights reserved.

1. Introduction Water, an inexpensive, nontoxic, noncorrosive and non-flammable solvent, provides remarkable advantages over common organic solvents both from economic and environmental points of view [1]. The use of water as a medium in organic reaction has received increasing attention and is currently one of the most important targets of sustainable chemistry [2]. So far, much progress has been made in this area, and the Suzuki–Miyaura reaction, which is a versatile and powerful tool for the construction of carbon–carbon bond, is one of the excellent examples [3–5]. Arylboronic acids, as a coupling partner, have been extensively applied in the Suzuki–Miyaura reaction. However, arylboronic acids are sp2-hybridized intermediates, which are subject to cyclic trimerization with loss of water [6]. Moreover, many arylboronic acids are prone to protodeboronation or homocoupling in the Suzuki– Miyaura reaction. Thus, these disadvantages of arylboronic acids limit their applications. Recently, there has been increased interest in the use of potassium organotrifluoroborates as coupling partners for the Suzuki–Miyaura reaction [7–14]. Potassium aryltrifluoroborates offer several advantages compared with arylboronic acids, being similar to arylboronic acids in functional group tolerance, but exhibiting better stability toward air and water [8]. These tetracoordinate species are more easily purified than arylboronic acids, and can be stored indefinitely without any special precautions [6]. These positive features are

⁎ Corresponding author. E-mail address: [email protected] (C. Liu).

http://dx.doi.org/10.1016/j.catcom.2015.05.025 1566-7367/© 2015 Elsevier B.V. All rights reserved.

very appealing for the pharmaceutical industry. Since the pioneering studies reported by Genêt [15,16], Xia [17] and Molander [18,19], a lot of efforts have been made by numerous groups [9,12,20,21] or companies [22,23] in the development of highly active approaches for the Suzuki–Miyaura reaction of potassium organotrifluoroborates. However, there are only a few reports on the use of pure water as the reaction medium. In 2003, Molander's group [24] reported that the Suzuki–Miyaura reaction of potassium aryltrifluoroborates and water-soluble aryl bromides bearing a –COOH or –OH group could take place in pure water with good yields. Nájera et al. [25] described that cross-couplings of potassium aryltrifluoroborates with aryl chlorides were performed smoothly in refluxing water, and a precatalyst of 4-hydroxyacetophenone oximederived palladacycle and TBAB were required in the reaction. Very recently, Liu et al. reported a Pd(OAc)2-catalyzed Suzuki–Miyaura reaction of potassium organotrifluoroborates at 80 °C in PEG/water [26] or ionic liquids/water [27], delivering the biaryl products in moderate to excellent yields. Up to now, the Suzuki–Miyaura reaction of potassium aryltrifluoroborates in water requires additives or suffers from a limited scope of substrates. In the past several years, our group has been involved in the development of green and efficient procedures for the Suzuki–Miyaura reaction [28–30]. Herein, we wish to report a simple and efficient catalytic system for the palladium-catalyzed Suzuki– Miyaura reaction of aryl/heteroaryl halides with potassium aryltrifluoroborates in pure water without any additive. This catalytic system, using Pd(OAc)2 as catalyst and (i-Pr)2NH as base, demonstrates high efficiency for a broad range of substrates. In addition, this procedure can be conveniently scaled up to gram-scale level and the desired products can be isolated in good yields by filtration and recrystallization.

82

C. Liu et al. / Catalysis Communications 69 (2015) 81–85

2. Experimental

Table 2 The effect of the palladium species and temperature on the Suzuki–Miyaura reactiona.

2.1. General procedure for the Suzuki–Miyaura reaction. A mixture of potassium aryltrifluoroborates (0.6 mmol), aryl bromides (0.5 mmol), (i-Pr)2NH (1 mmol), Pd(OAc)2 (0.5 mol%), and H2O (1 mL) was stirred at 100 °C in air for the indicated time. The reaction mixture was added to brine (10 mL) and extracted with ethyl acetate (3 × 10 mL). The combined organic layers were concentrated in vacuo and the product was isolated by short chromatography. 3. Results and discussion To optimize reaction conditions, the effects of various parameters on the coupling reaction were explored. As reported in the literature, a base is important for promoting the Suzuki–Miyaura reaction of potassium aryltrifluoroborates [24]. Thus, we initially studied the effect of a base on the model reaction of 4-bromoanisole (0.5 mmol) with potassium phenyltrifluoroborate (0.6 mmol) in 1 mL water with 0.5 mol% Pd(OAc)2 at 100 °C. The results are summarized in Table 1. A watersoluble inorganic base such as K2CO3, Na2CO3, Cs2CO3, NaHCO3, etc., demonstrated low activity in the present protocol (Table 1, entries 1– 6). Subsequently, several organic bases were examined. For example, Et3N, a typical organic base in the palladium-catalyzed Suzuki–Miyaura reaction, provided a disappointing result (Table 1, entry 7). DABCO (1,4diazabicyclo[2.2.2]octane) gave a 43% yield (Table 1, entries 8 and 9). It is clear that the most efficient base in the present catalytic system is (i-Pr)2NH, which provided an 86% yield in 2 h (Table 1, entry 9). The next investigation was to optimize the conditions including palladium precatalysts and temperature in the same model reaction. As shown in Table 2, PdCl2, PdCl2(CH3CN)2, and Pd2(dba)3 (Table 2 entries 1–3) showed moderate catalytic activity in this system, while Pd(OAc)2 was effective and an 86% yield of the product was obtained (Table 2, entry 4). However, if the loading of Pd(OAc)2 was decreased to 0.25 mol%, only a 63% yield was observed (Table 2, entry 5). Thus, 0.5 mol% Pd(OAc)2 was chosen as the catalyst for the next study. The effect of temperature on this reaction was also evaluated. The coupling reaction performed at 80 °C provided the cross-coupled product in 59% yield (Table 2, entry 6). Thus, the optimum reaction conditions for this cross-coupling were found to be 0.5 mol% Pd(OAc)2, 2 equiv. of (iPr)2NH, and 100 °C in water. In general, various additives such as tetrabutylammonium bromide (TBAB) or cetyltrimethylammonium bromide (CTAB) are required for effective reaction progress in aqueous Suzuki–Miyaura reaction [31, 32]. Interestingly, in this catalytic system, the addition of TBAB could not promote the reaction and an 85% yield was obtained in 2 h (Table 1, entry 10). To further investigate the effect of a base, a kinetic

Entry

Catalyst

Temperature (°C)

Yieldb (%)

1 2 3 4 5 6

PdCl2 PdCl2(CH3CN)2 Pd2(dba)3 Pd(OAc)2 Pd(OAc)2 Pd(OAc)2

100 100 100 100 100 80

68 56 35 86 63c 59

a Reaction conditions: 4-bromoanisole (0.5 mmol), potassium phenyltrifluoroborate (0.6 mmol), catalyst (0.5 mol%), (i-Pr)2NH (1.0 mmol), H2O (1 mL), 100 °C, and 2 h, under air. b Isolated yield. c Pd(OAc)2 0.25 mol%.

study of the Suzuki–Miyaura reaction was performed in the presence of 0.5 mol% Pd(OAc)2 at 100 °C in water with different bases. As shown in Fig. 1 (curve a), the coupling reaction proceeded smoothly with 2.0 equiv. (i-Pr)2NH and an 86% yield was achieved in 2 h. However, only a 23% yield was observed when using 2.0 equiv. K2CO3 as base (curve c). Interestingly, a 54% yield of the coupling product could be obtained when using 2.0 equiv. K2CO3 and 0.05 equiv. (i-Pr)2NH (curve b). These results indicated that (i-Pr)2NH could promote the reaction efficiently. It is supposed that the reason for the high efficiency is that (i-Pr)2NH acts not only as a base, but also as a ligand, which has a much higher tendency to coordinate to palladium to form the active species as reported by Boykin and Tao [33,34]. With the optimized conditions in hand, we further studied the scope and limitations of substrates. Various 4-substituted aryl bromides, bearing either electron-withdrawing or electron-donating groups, provided the corresponding cross coupling products in excellent yields (Table 3, entries 1–8). For examples, 4-bromophenol was successfully coupled with potassium phenyltrifluoroborate providing a 96% yield in 30 min (Table 3, entry 7), which was more effective compared with the reported method [24]. The cross-coupling of 1-bromo-4-methylbenzene and potassium phenyltrifluoroborate gave the product an 86% isolated yield in 90 min (Table 3, entry 8). 3-Bromonitrobenzene could also couple with potassium phenyltrifluoroborate, resulting in a 94% yield in 60 min (Table 3, entry 9). These results showed that this catalytic system could tolerate aryl bromides with both hydrophilic groups and hydrophobic groups, and the electronic effect had little influence on the reactivity of the aryl bromides. The cross-coupling reaction proceeded

Table 1 The effect of base on the Suzuki–Miyaura reactiona.

Entry

Base

Yieldb(%)

1 2 3 4 5 6 7 8 9 10

K2CO3 Na2CO3 NaHCO3 Cs2CO3 NaOH K3PO4·3H2O Et3N DABCO (i-Pr)2NH (i-Pr)2NH

23 25 20 21 14 19 53 43 86 85c

a Reaction conditions: 4-bromoanisole (0.5 mmol), potassium phenyltrifluoroborate (0.6 mmol), base (1.0 mmol), Pd(OAc)2 (0.5 mol%), H2O (1 mL), 100 °C, and 2 h, under air. b Isolated yield. c TBAB (0.25 mmol), 2 h.

Fig. 1. Isolated yield vs. time curves of the Suzuki–Miyaura reaction of 4-bromoanisole (0.5 mmol) with potassium phenyltrifluoroborate (0.6 mmol) in water at 100 °C with 0.5 mol% Pd(OAc)2 in the presence of different bases. (a) (i-Pr)2NH (1.0 mmol), (b) K2CO3 (1.0 mmol) and (i-Pr)2NH (0.05 equiv.), and (c) K2CO3 (1.0 mmol).

C. Liu et al. / Catalysis Communications 69 (2015) 81–85

83

Table 3 The Suzuki–Miyaura reaction of aryl halides with potassium aryltrifluoroboratea.

Entry

Ar–Br

Ar–BF3K

Time (min)

Yieldb (%)

1

30

96

2

60

96

3

60

95

4

60

94

5

90

93

6

120

86

7

30

96

8

90

86

9

60

94

10

30

95

11

90

93

12

90

84

13

30

95

14

60

94

15

20

96

16

60

92

17

30

95

18

60

96

19

60

92

20

60

94

21

60

92

22

120

95

23

120

82

24

120

65c

a b c

Reaction conditions: aryl halides (0.5 mmol), potassium aryltrifluoroborate (0.6 mmol), (i-Pr)2NH (1.0 mmol), Pd(OAc)2 (0.5 mol%), H2O (1 mL), and 100 °C, under air. Isolated yields. Pd(OAc)2 (2 mol%).

also smoothly even increasing the steric effect of aryl bromides (Table 3, entries 10–12). To further investigate the catalytic activity of this system, we chose the potassium aryltrifluoroborates containing an electron-donating or electron-withdrawing group as coupling partners. The crosscoupling reactions of aryl bromides with electron-rich potassium aryltrifluoroborate proceeded smoothly (Table 3, entries 13–17). The potassium 3-methylphenyltrifluoroborate also underwent the Suzuki– Miyaura reaction readily (Table 3, entries 18 and 19). Besides, this system tolerated the functional groups in the ortho position of the potassium aryltrifluoroborates. In comparison with the non-sterically hindered potassium aryltrifluoroborates, the ortho-substituted substrates gave almost the same yields (Table 3, entries 20 and 21). However, potassium aryltrifluoroborate with electron-withdrawing groups showed a slightly lower reactivity. Potassium 4-cyanophenyltrifluoroborate completed the coupling reaction in 120 min (Table 3, entries 22 and 23). The coupling reaction of 4-chloronitrobenzene with potassium phenyltrifluoroborate afforded a 65% yield of the product using 2 mol% Pd(OAc)2 in 120 min (Table 3, entry 24). Heterobiaryls are ubiquitous in natural products, pharmacologically active compounds, polymers, and other functional materials. Thus, we next investigated the Suzuki–Miyaura reaction of heteroaryl bromides with potassium aryltrifluoroborate in this system. The results are

summarized in Table 4. 2-Bromopyridine and 6-substituted 2bromopyridine all performed the Suzuki–Miyaura reaction smoothly and delivered the desired products in good yields in 2 h (Table 4, entries 1–3). 3-Bromopyridine and 5-bromo-2-methoxypyridine were coupled with potassium phenyltrifluoroborate to afford the desired products with 83% and 94% yields, respectively (Table 4, entries 4 and 5). 5-Bromopyrimidine could also couple with potassium phenyltrifluoroborate and afforded the target product a 96% yield in 2 h (Table 4, entry 6). It is noteworthy that the coupling reaction of potassium phenyltrifluoroborate with 2-bromoquinoline or 3bromoquinoline proceeded well to provide the cross-coupled products in excellent yields (Table 4, entries 7 and 8). The Suzuki– Miyaura reactions of 2-bromothiophene or 3-bromothiophene with potassium phenyltrifluoroborate were also studied in this system. 3-Bromothiophene provided the product in higher yield than 2bromothiophene, and the isolated yields were 65% and 43%, respectively (Table 4, entries 9 and 10). The reaction of 5-bromopyrimidine with electron-rich potassium 4-methylphenyltrifluoroborate or electron-poor potassium 4-fluorophenyltrifluoroborate provided the heterobiaryl products with more than 90% isolated yields (Table 4, entries 11 and 12). In addition, the cross-coupling involving potassium heteroaryltrifluoroborates were also performed in this

84

C. Liu et al. / Catalysis Communications 69 (2015) 81–85

Table 4 The Suzuki–Miyaura reaction of heteroaryl halides with potassium aryltrifluoroboratea. PdðOAC Þ2

Heteroaryl halides þ Ar−B F3 K →H2 O Entry

Heteroaryl−Ar Heteroaryl halides

Ar–BF3K

Yieldb (%)

1

85

2

91

3

95

4

83

5

94

6

96

7

92

8

90

9

65

10

43

11

95

12

94

13

90c

14

Tracec

15

60

16

78

17

90c

18

78c

a b c

Reaction conditions: heteroaryl halides (0.5 mmol), potassium aryltrifluoroborate (0.6 mmol), (i-Pr)2NH (1.0 mmol), Pd(OAc)2 (2 mol%), H2O (1 mL), 100 °C, and 2 h, under air. Isolated yields. 12 h.

system. 5-Bromopyrimidine coupled with potassium 2thiophenetrifluoroborate gave the desired product in 90% yield (Table 4, entry 13). However, the coupling reactions involving potassium 4-pyridyltrifluoroborate provided a trace of the product (Table 4, entry 14). In further studies, heteroaryl chlorides were chosen as the coupling partner. The cross-coupling between potassium phenyltrifluoroborate and 2-chloropyridine or 5-chloropyrimidine

afforded the corresponding product moderate yields (Table 4, entries 15 and 16). The coupling reactions involving potassium thiophenetrifluoroborate provided the desired products in 90% and 78% yields, respectively (Table 4, entries 17 and 18). The drug of valsartan (Diovan) is therapeutically useful in treating congestive heart failure and high blood pressure [35]. The common structural element, a biphenyl unit of 2-cyano-4′-methylbiphenyl, is essential

Scheme 1. Simple isolation of biaryl compounds by filtration and recrystallization.

C. Liu et al. / Catalysis Communications 69 (2015) 81–85

for the binding affinity to the receptor and for the oral bioavailability. Thus, it is highly desirable to develop a simple and efficient method for prepare 2-cyano-4′-methylbiphenyl. As shown in Scheme 1, the present procedure was conveniently scaled up to gram scales to prepare 2-cyano4′-methylbiphenyl. More interestingly, the product of 2-cyano-4′methylbiphenyl (1.2 g, 80% yield) was successfully isolated with high purity by simple filtration and recrystallization from 20 mL petroleum ether. This method avoids the use of a large amount of organic solvent during the separation process, which would be more favorable from a safe and environmental perspective. In addition, 1.05 g 5-(p-tolyl)pyrimidine was also prepared by this method and good purity was confirm by 1H NMR (see Supplementary data). 4. Conclusions

References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15]

In conclusion, we have developed a simple and green protocol for the Suzuki–Miyaura reaction of potassium aryltrifluoroborates in pure water without any additive. This catalytic system demonstrates high efficiency toward a wide range of (hetero)aryl halides, and the base of (i-Pr)2NH could promote the reaction efficiently. Further work to explore the exact function of (i-Pr)2NH in the system is currently under investigation in our laboratory. Acknowledgements The authors thank the financial support from the National Natural Science Foundation of China (21276043 and 21076034). Appendix A. Supplementary data Supplementary data to this article can be found online at http://dx. doi.org/10.1016/j.catcom.2015.05.025.

85

[16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35]

C.-J. Li, L. Chen, Chem. Soc. Rev. 35 (2006) 68–82. C.I. Herrerías, X. Yao, Z. Li, C.-J. Li, Chem. Rev. 107 (2007) 2546–2562. C.-J. Li, Chem. Rev. 105 (2005) 3095–3166. N. Miyaura, A. Suzuki, Chem. Rev. 95 (1995) 2457–2483. V. Polshettiwar, A. Decottignies, C. Len, A. Fihri, ChemSusChem 3 (2010) 502–522. D.G. Hall, Boronic Acids: Preparation and Applications in Organic Synthesis, John Wiley & Sons, Medicine and Materials, 2012. S. Darses, J.-P. Genêt, Eur. J. Org. Chem. (2003) 4313–4327. S. Darses, J.-P. Genêt, Chem. Rev. 108 (2008) 288–325. G.A. Molander, B. Canturk, L.E. Kennedy, J. Org. Chem. 74 (2008) 973–980. G.A. Molander, N. Ellis, Acc. Chem. Res. 40 (2007) 275–286. G.A. Molander, D. Ryu, M. Hosseini-Sarvari, R. Devulapally, D.G. Seapy, J. Org. Chem. 78 (2013) 6648–6656. W. Ren, J. Li, D. Zou, Y. Wu, Y. Wu, Tetrahedron 68 (2012) 1351–1358. H.A. Stefani, R. Cella, A.S. Vieira, Tetrahedron 63 (2007) 3623–3658. S.D. Dreher, S.E. Lim, D.L. Sandrock, G.A. Molander, J. Org. Chem. 74 (2009) 3626–3631. S. Darses, J.P. Genêt, J.L. Brayer, J.P. Demoute, Tetrahedron Lett. 38 (1997) 4393–4396. S. Darses, G. Michaud, J.P. Genêt, Eur. J. Org. Chem. (1999) 1875–1883. M. Xia, Z.-C. Chen, Synth. Commun. 29 (1999) 2457–2465. G.A. Molander, B. Biolatto, Org. Lett. 4 (2002) 1867–1870. G.A. Molander, M.R. Rivero, Org. Lett. 4 (2002) 107–109. T.E. Barder, S.L. Buchwald, Org. Lett. 6 (2004) 2649–2652. R.A. Batey, T.D. Quach, Tetrahedron Lett. 42 (2001) 9099–9103. D.J. Calderwood, D.N. Johnston, P. Rafferty, H. Twigger, R. Munschauer, L. Arnold, (Knoll A. G. Chemische Fabriken) WO. Patent 9841525, 1998. K. Puentener, M. Scalone, (Hoffmann-La Roche AG) EP Patent 1057831, 2000. G.A. Molander, B. Biolatto, J. Org. Chem. 68 (2003) 4302–4314. E. Alacid, C. Nájera, Org. Lett. 10 (2008) 5011–5014. L. Liu, Y. Dong, N. Tang, Green Chem. 16 (2014) 2185–2189. L. Liu, Y. Dong, B. Pang, J. Ma, J. Org. Chem. 79 (2014) 7193–7198. C. Liu, Q. Ni, P. Hu, J. Qiu, Org. Biomol. Chem. 9 (2011) 1054–1060. C. Liu, W. Yang, Chem. Commun. (2009) 6267–6269. C. Liu, Y. Zhang, N. Liu, J. Qiu, Green Chem. 14 (2012) 2999–3003. B. Yuan, Y. Pan, Y. Li, B. Yin, H. Jiang, Angew. Chem. Int. Ed. 49 (2010) 4054–4058. E. Alacid, C. Nájera, J. Org. Chem. 74 (2009) 2321–2327. B. Tao, D.W. Boykin, J. Org. Chem. 69 (2004) 4330–4335. B. Tao, D.W. Boykin, Tetrahedron Lett. 44 (2003) 7993–7996. R.R. Wexler, W.J. Greenlee, J.D. Irvin, M.R. Goldberg, K. Prendergast, R.D. Smith, P.B. Timmermans, J. Med. Chem. 39 (1996) 625–656.