Amide as an efficient ligand in the palladium-catalyzed Suzuki coupling reaction in water/ethanol un Amide as an efficient ligand in the palladium-catalyzed Suzuki coupling reaction in water/ethanol un

Amide as an efficient ligand in the palladium-catalyzed Suzuki coupling reaction in water/ethanol un

  • 期刊名字:中国化学快报(英文版)
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  • 论文作者:Hai Yang Liu,Kun Wang,Hai Yan
  • 作者单位:Key Lab of Green Chemistry and Technology
  • 更新时间:2020-10-22
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象Availableonlineatwww.sciencedirect.comCHINESEScience directCHEMICALLETTERSELSEVIERChinese Chemical Letters 22(2011)738-740www.elsevier.com/locate/ccleAmide as an efficient ligand in the palladium-catalyzed suzukicoupling reaction in water/ethanol under aerobic conditionsHai Yang Liu, Kun Wang, Hai Yan Fu, Mao Lin Yuan, Hua Chen", Rui Xiang LiKey Lab of Green Chemistry and Technology, Ministry of Education, the institute of Homogeneous Catalysis,College of Chemistry, Sichuan University, Chengdu 610064, ChinaReceived 15 October 2010AbstractAmide, which is derived from proline and is inexpensive and air-stable, has been synthesized and characterized by HNMR, CNMR, and MS. It was found to be an efficient ligand in the palladium-catalyzed Suzuki cross-coupling reaction. In the pd/amidcatalytic system, aryl bromides can be coupled with phenylboronic acid in ethanol/water(1: 2; v/v)in excellent yields even with alow Pd loading of 0.01 mol%. Moreover, the scope of the reaction is broad, and a wide variety of functional groups are tolerant.C 2011 Hua Chen. Published by Elsevier B V. on behalf of Chinese Chemical Society. All rights reserved.Keywords: Suzuki cross-coupling: Palladium catalyst; Aryl bromides: Amide: WaterIn the past two decades, the palladium-catalyzed Suzuki cross-coupling reaction of aryl halides with arylboronic acidhas evolved into one of the most valuable synthetic processes to form biaryls [ 1-4]. Phosphine-based ligands have beenwidely used for the palladium-catalyzed coupling reaction [5-8]. However, most of these phosphines are sensitive to airand moisture and they are also expensive and toxic. Therefore, a few phosphine-free ligands, such asN-heterocyliccarbenes [9-12], diimines [ 13], diaminos [141, N, N, N-ligands [15], O,N, N, O-ligands [16] and N, N,O-ligands[17] havebeen studied for the Suzuki reaction. To the best of our knowledge, there are few papers about using amide as ligands forthe Suzuki cross-coupling reaction. Herein, we report a new kind of ligands, which is derived from proline( compound 1),for Suzuki cross-coupling reaction in water and ethanol under aerobic conditions. Our synthetic route can be clearly seenin Scheme 1 [18, 19]. The new ligand (compound 3)has been elucidated by H NMR,C NMR and MS [20J1. ExperimentalHandC400 MHz spectra were recorded on a bruker spectrometer using CDCl3 as solvent and tetramethylsilaneITMS] as intermal standard in all cases. Melting points were determined on a Thomas-Hoover capillary melting pointapparatus. High-resolution mass spectra were recorded on a Q-TOF mass spectrometry( Waters) equipped withZ-spray ionization source. The isolation of pure products was carried out via Silica gel column(Silica gel 300-400mesh). Aryl halides were used directly as obtained commercially without any process.中国煤化工Corresponding author.E-mail address: scuhchen 163 com(H. Chen)CNMHG1001-8417/s-see front matter C 2011 Hua Chen. Published by Elsevier B V. on behalf of Chinese Chemical Society. All rights reserved.1016 j cclet.2010.12048H.Y. Liu et al /Chinese Chemical Letters 22(2011)738-740CODEScheme 1. Reagents and conditions(a)(1) MeOH, KcO3, RT, 0.5 h; (2)CICOOEt, 0C. 12 h; (b)DMF, BuOK, 3-NH2-CH4OMe 140C, 30 min(75-80%)All reactions were performed under aerobic conditions. In the first step, the referred solution(CP=1.0×l0· mmol/mL,Ct2.0 X 10 mmol/mL, water as solvent)was prepared. A single-neckedtube (rinner=1.2 cm, L=17.5 cm) equipped with a magnetic stir bar was charged with 1.0 mmol of aryl halides,1.5 mmol of phenylboronic acid and 2 mmol base under aerobic conditions. Then, 1.0 mL referred solution and 2.0 mLwater and 1. 5 mL ethanol was added into the tube. the reaction mixture was stirred in oil bath with pre-arrangedtemperature for appropriate reaction time. After the reaction was completed, 3 mL water was added, and the aqueousphase was extracted with EtOAc(8 mL X3). The organic phase was dried over anhydrous Na2SO4 and concentratedunder reduced pressure after filtered. The residue was then purified by column chromatography on silica gel column2. Results and discussionWe initially tested the reaction of phenylboronic acid with 4-bromoanisole as a model reaction in EtOH/H2O(1: 2v/v)in the presence of ligand and PdCl2(Scheme 2). The effects of various inorganic and organic bases on the Suzukicross-coupling reaction were investigated. Among them, K3 PO4 and Cs2CO3 are effective for the reactionConsidering the high-cost of Cs2CO3, we chose the mild base K 3 PO4 in all the subsequent reactionThe temperature ranging from 25"C to 90C was screened for the suitable reaction temperature in the presence of0.01 mol PdCl2 and 0.02 mol% ligand. The GC yield of 4-MeOC6Ha-Ph was only 7% in 10 h at room temperature,and increased significantly with the temperature rising. When the temperature rose up to 80C, the GC yield wasincreased to 99% while only 26% yield can be obtained in the absence of ligand in 1h.Under the optimized condition with PdCl2(0.01 mol%), ligand (0.02 mol%), K, POA(2 equiv)in 4.5 mL EtOH/H2O mixture, we examined the cross-coupling reaction of a wide range of phenylboronic acid with various arylhalides, and the results were summarized in table 1In the above Pd-catalyzed Suzuki cross-coupling system, the Suzuki reaction was found to afford good to excellentyield for the desired product. For example, in the presence of 0.01 mol% PdCl2 and 0.02 mol% ligand, an excellentconversion(97%)and high ToN (9700) for the substrate 4-BrC6HOMe was obtained at 80C in I h, and a moderateyield(58%)still could be obtained even the Pd-loading was reduced to 0.001 mol%. As can be seen from Table 1(entries 1-12), various aryl bromides with electron rich or deficient group were converted efficiently to the targetproducts in good to excellent yields within I h. In spite of the hindrance of 2-BrC6H4Me, 2-BrCH4NO2 and 2-bromo-m-xylene, a good yield of desired products was still obtained(Table 1, entries 6, 9, and 12 ) The coupling ofphenylboronic acid with heteroaryl bromides, such as 3-bromopyridine, 3-bromoquinoline and 5-bromopyrimidinewas also investigated. The target products were also obtained in good yields(Table 1, entries 13-15)and high toNs(8100, 9500 and 9400)were obtained when the reaction temperature was elevated to 90C(refluxed temperature)andthe time was prolonged to 6 h. The coupling reaction of phenylboronic acid with activated aryl chloride such as4-CIC6H4NOz and 4-CIC6HaCF3 was carried out with 0.5 mol% catalyst loading. But the yield was only 52% and 39%(Table l, entries 16 and 17)respectively, even though the Pd-loading was raised and the reaction temperature waselevated to 90C and the reaction time was prolonged to 20 h中国煤化工+CNMHGOScheme 2. The model reaction in EtOH/H2OH Y Liu et al. /Chinese Chemical Letters 22(2011)738-740Table 1The coupling reaction of aryl halides with phenylboronic acid in waterlethanol ArX +Ph-B(On/H2O/ENOH,K,PO4Ar-Ph x= Br, ClPd loadings(mol%)Temp.(%time(h)Yield(%)TOND198004-BrC6H,OMe4-BrCHOMe8020580001234567890123453-BrC6HOMe804-BrC6HeMe2-BrC,H,M4-BrC6H, CF0014-BrC6HNO2800014-BrC, COMe4-BrC6H4CHO0012-Bromo-m-xylene3-Bromopyridine001908989848829%88%92810095005-Bromopyrimidine0014-CIC6H4NO90/204-CIC,H, CF39020Reaction conditions: n(Lyn(Pd)=2, aryl halide( 1.0 mmoD), phenyl boronic( 1.5 mmol), Ky PO4(2.0 mmol), H2o (3.0 mL), and ethanol(1.5 mL).Isolated yield.In conclusion, we have successfully synthesized and characterized a novel ligand derived from proline, which hasbeen shown to be highly effective in the Suzuki cross-coupling reaction of phenylboronic acid with differentsubstituted bromobenzenes and heteroaryl bromides under aerobic conditions in EtOH/H2O (1: 2;v/v)AcknowledgmentWe would like to gratefully acknowledge the analytical and Testing Center of Sichuan University for providing thespectroscopic data.References[I] N Miyaura, A Suzuki, Chem. Rev. 95(1995)2457[2] A Suzuki, J Organomet Chem. 576(1999)147.[3]K. Pomeisl, A. Holy, R. Pohl, et al. Tetrahedron 65(2009)8486[4] J.P. Heiskanen, O.E. Hormi, Tetrahedron 65(2009)518.[5] A. Zapf, A. Ehrentraut, M. Beller, Angew. Chem. Int. Ed, 39(2000)4153[6] R.C. Smith, R.A. Woloszynek, w. Chen, et al. Tetrahedron Lett. 45(2004)8327[7] K. Billingsley, S.L. Buchwald, J. Am. Chem. Soc. 129(2007)3358.[8] C. Wolf, K. Ekov, Eur J. Org. Chem. (2006)1917.[ 9] T. Karthikeyan, S Sankararaman, Tetrahedron 50(2009)5834O] F.w. Li, S.Q. Bai, T.S. Andy Hor, Organometallics 27(2008)672.[11]G. Altenhof, R. Goddard, C W. Lehmann, et al. Angew. Chem. Int. Ed. 42(2003)3690.[12] M B. Andrus, C Song. Org. Lett. 3(2001)3761[13]J. Zhou, x.M. Guo, CZ Tu, et al. J Organomet Chem. 694(2009)697.[14] J M. Lu, H Ma, S.S. Li, et al. Tetrahedron 66(2010)5185[15] D H. Lee, Y.H. Lee, D. Kim ll, et al. Tetrahedron 64(2008)7178[16] S Mohanty, D. Suresh, M.S. Balakrishna, et al. J Organomet. Chem. 694(2009)2114[17] S.A. Patil, C M. Weng, P.C. Huang, et al. Tetrahedron 65 (2009)2889[18] J.V. Bhaskar Kanth, M. Periasamy. Tetrahedron 49(1993)5127[19] L. Perreux, A. Loupy, M. Delmotte, Tetrahedron 59(2003)2185中国煤化工[20] Selected analytical data for amide ligand: mp 178-181C; H NMR(400 MHCN MHGm, 2H, CH2), 2.2('m, 2H,CH), 4.6(m, 1H. CH), 3.9(s, 6H, OCHy-OCH3). 6.3(m, IH, CONH), 9.4(m,(m, on Arn-ArH); C NMR(400 MHz,cDcl)6169.79,160.23,16007,15551,13957,13953,12964,12948.112.39,11208,l0.l3,109.31,106.15,105.26,60.%6,55.28,55.26,4668,27.23,and2528; HRMS Calcd.forC2H2NO4370.1760M], found:370.1689

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