Synlett 2012; 23(10): 1534-1540
DOI: 10.1055/s-0031-1290680
letter
© Georg Thieme Verlag Stuttgart · New York

Phenyliodine Bis(trifluoroacetate) Mediated Intramolecular Oxidative Coupling of Electron-Rich N-Phenyl Benzamides

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
› Author Affiliations
Further Information

Publication History

Received: 15 February 2012

Accepted after revision: 03 April 2012

Publication Date:
29 May 2012 (online)


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.

Supporting Information

 
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  • 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 Products
    6-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