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Synlett 2012; 23(10): 1534-1540
DOI: 10.1055/s-0031-1290680
DOI: 10.1055/s-0031-1290680
letter
Phenyliodine Bis(trifluoroacetate) Mediated Intramolecular Oxidative Coupling of Electron-Rich N-Phenyl Benzamides
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.
Key words
hypervalent iodine - N-phenyl benzamides - cyclization - oxidative coupling - benzoxazolesSupporting Information
- for this article is available online at http://www.thieme-connect.com/ejournals/toc/synlett.
- Supporting Information
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References and Notes
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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)
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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
For examples of intramolecular aryl–aryl coupling, see:
For examples of intermolecular aryl–aryl coupling, please see:
For examples of intramolecular C–N coupling, see:
For examples of intramolecular C–O coupling, see: