Synlett, Table of Contents Synlett 2012; 23(10): 1534-1540DOI: 10.1055/s-0031-1290680 letter © Georg Thieme Verlag Stuttgart · New YorkPhenyliodine Bis(trifluoroacetate) Mediated Intramolecular Oxidative Coupling of Electron-Rich N-Phenyl Benzamides Authors Author Affiliations Zhengsen Yu State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000, P. R. of China, Email: yuwei@lzu.edu.cn Lijuan Ma State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000, P. R. of China, Email: yuwei@lzu.edu.cn Wei Yu* State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000, P. R. of China, Email: yuwei@lzu.edu.cn Recommend Article Abstract Buy Article(opens in new window) All articles of this category(opens in new window) Abstract The intramolecular oxidative C–O coupling of N-(4-alkoxy-phenyl) and N-(4-acetamido-phenyl) benzamides was achieved under metal-free conditions by using phenyliodine bis(trifluoroacetate) as oxidant and TMSOTf as catalyst. The reactions afford benzoxazole products in high yields. Key words Key wordshypervalent iodine - N-phenyl benzamides - cyclization - oxidative coupling - benzoxazoles Full Text References References and Notes 1a Zhdankin VV, Stang PJ. Chem. Rev. 2002; 102: 2523 1b Zhdankin VV, Stang PJ. Chem. Rev. 2008; 108: 5299 1c Zhdankin VV. ARKIVOC 2009; (i): 1 For examples of intramolecular aryl–aryl coupling, see: 2a Takada T, Arisawa M, Gyoten M, Hamada R, Tohma H, Kita Y. J. Org. Chem. 1998; 63: 7698 2b Olivera R, SanMartin R, Pascual S, Herrero M, Domínguez E. 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Chem. 2009; 72: 4272 11 Barlin GB, Riggs NV. J. Chem. Soc. 1954; 3125 12 Kokil PB, Patil SD, Ravindranathan T, Nair PM. Tetrahedron Lett. 1979; 20: 989 13 Liu H, Wang X, Gu Y. Org. Biomol. Chem. 2011; 9: 1614 14 Itoh N, Sakamoto T, Miyazawa E, Kikugawa Y. J. Org. Chem. 2002; 67: 7424 15 Moreno I, Tellitu I, Etayo J, SanMartin R, Domínguez E. Tetrahedron 2001; 57: 5403 16 General Procedure for the Reactions of 1 (or 5) To a stirred MeCN solution (40 mL) containing 1 (or 5, 0.5 mmol) and TMSOTf (1.0 mmol) was added dropwise PIFA (0.6 mmol) in MeCN (10 mL). The stirring was continued at r.t. for another 5 min. The mixture was then poured into a sat. NaHCO3 solution (100 mL), and the product was extracted with EtOAc (2 × 100 mL). The combined organic phase was washed with brine, and then dried with anhyd MgSO4. After filtration, the filtrate was concentrated under reduced pressure, and the residual was treated with flash column chromatography to give 2 (or 6) 17 Typical Spectroscopic Data for the Products6-Ethoxy-2-(4-bromophenyl)benzo[d]oxazole (2e) White solid; mp 136–138 °C. 1H NMR (400 MHz, CDCl3): δ = 1.46 (t, 3 H, J = 7.2 Hz, CH 3CH2), 4.08 (q, 2 H, J = 7.2 Hz, OCH2), 6.95 (dd, 1 H, J = 8.8, 2.4 Hz, C5-H), 7.06 (d, 1 H, J = 2.4 Hz, C7-H), 7.61 (d, 1 H, J = 8.8 Hz, C4-H), 7.62 (d, 2 H, J = 8.4 Hz, 4-BrPhH), 8.04 (d, 2 H, J = 8.4 Hz, 4-BrPhH). 13C NMR (100 MHz, CDCl3): δ = 14.8, 64.2, 96.0, 113.5, 120.0, 125.6, 126.3, 128.5, 132.1, 135.6, 151.6, 157.8, 161.2. MS (EI): m/z (rel. int., %) = 317 (71) [M+], 262 (7), 210 (10), 183 (21), 79 (54), 51 (100). ESI-HRMS: m/z calcd for C15H12BrNO2 + H: 318.0124; found: 318.0134 N-{2-Phenylbenzo[d]oxazol-6-yl}acetamide (6a) Light yellow solid; mp 176–177 °C. 1H NMR (400 MHz, acetone-d 6): δ = 2.13 (s, 3 H, CH3CO), 7.38 (dd, 1 H, J = 8.8, 1.6 Hz, C5-H), 7.59–7.61 (m, 3 H, PhH), 7.64 (d, 1 H, J = 8.8 Hz, C4-H), 8.21–8.24 (m, 2 H, PhH), 8.39 (d, 1 H, J = 1.6 Hz, C7-H), 9.50 (br s, 1 H, NH). 13C NMR (100 MHz, acetone-d 6): δ = 24.4, 102.3, 117.2, 120.5, 128.1, 128.2, 130.0, 132.3, 138.6, 138.7, 152.0, 163.3, 169.2. MS (EI): m/z (rel. int., %) = 252 (39) [M+], 210 (100), 149 (6). ESI-HRMS: m/z calcd for C15H12N2O2 + H: 253.0972; found: 253.0973 N-{2-(4-Methoxyphenyl)benzo[d]oxazol-6-yl}acetamide (6b) Light yellow solid; mp 187–189 °C. 1H NMR (400 MHz, DMSO-d 6): δ = 2.09 (s, 3 H, CH3CO), 3.85 (s, 3 H, OCH3), 7.13 (d, 2 H, J = 8.4 Hz, 4-MeOPhH), 7.37 (d, 1 H, J = 8.4 Hz, C5-H), 7.65 (d, 1 H, J = 8.8 Hz, C4-H), 8.09 (d, 2 H, J = 8.8 Hz, 4-MeOPhH), 8.22 (s, 1 H, C7-H), 10.22 (br s, 1 H, NH). 13C NMR (100 MHz, DMSO-d 6): δ = 24.0, 55.5, 101.1, 114.7, 116.2, 118.9, 119.1, 128.8, 136.9, 137.1, 150.2, 161.9, 162.0, 168.4. MS (EI): m/z (rel. int., %) = 282 (15) [M+], 240 (18), 225 (10), 178 (12), 149 (100). ESI-HRMS: m/z calcd for C16H14N2O3 + H: 283.1077; found: 283.1080 Supplementary Material Supplementary Material Supporting Information (PDF)
