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X. Liu, S. Zhang
LETTER
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(9) General Procedure for the Synthesis of Diaryl Ethers
A Schlenk tube equipped with a magnetic stir bar was
charged with p-toluidine (2a, 0.75 mmol, 80 mg), K2CO3
(138 mg, 1 mmol), Fe(acac)3 (34.4 mg, 20 mo%), and
Cu(OAc)2·H2O (20 mg, 20 mol%). Under a nitrogen
atmosphere, bromobenzene (1a, 0.5 mmol, 78.0 mg) was
added followed by dry DMF (0.8 mL). The reaction mixture
was then heated in an oil bath of 135 °C. After being stirred
at this temperature for 20 h, the mixture was cooled to r.t.
and diluted with Et2O. The resulting suspension was directly
filtered through a pad of Celite, the filtrate was concentrated,
and the crude mixtures were purified by column chroma-
tography on silica gel using PE–EtOAc solvent mixture as
the eluent.
(5) For pertinent reviews on Pd-catalyzed coupling reactions,
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Scholz, U. Adv. Synth. Catal. 2006, 348, 23. (c) Surry, D.
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1487. (b) Tamura, M.; Kochi, J. K. Synthesis 1971, 303.
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289.
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2007, 46, 934. (c) Song, R.; Deng, C.; Xie, Y.; Li, J.
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Xu, J.; Jiang, H.; Liu, H. Org. Lett. 2008, 10, 4513. (e) Du,
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2007. (f) Wang, Z.; Zhang, Y.; Fu, H.; Jiang, Y.; Zhao, Y.
4-Methyl-N-phenylaniline (3a)
1H NMR (400 MHz, CDCl3): d = 7.22 (t, J = 7.7 Hz, 2 H),
7.07 (d, J = 8.3 Hz, 2 H), 6.94–7.00 (m, 4 H), 6.87 (t, J = 7.3
Hz, 1 H), 5.58 (br s, 1 H), 2.29 (s, 3 H). 13C NMR (100 MHz,
CDCl3): d = 144.35, 140.68, 131.34, 130.30, 129.75, 120.71,
119.31, 117.26, 21.15. HRMS (EI+): m/z calcd for C13H13N
[M+]: 183.1048; found: 183.1051.
Ethyl 1-p-Tolyl-1H-imidazole-4-carboxylate (Table 3,
Entry 5)
1H NMR (400 MHz, CDCl3): d = 7.93 (s, 1 H), 7.82 (s, 1 H),
7.30 (s, 4 H), 4.41 (q, J = 7.1 Hz, 2 H), 2.42 (s, 3 H), 1.41 (t,
J = 7.1 Hz, 3 H). 13C NMR (75 MHz, CDCl3): d = 163.25,
138.99, 136.77, 135.30, 134.50, 131.02, 124.56, 122.02,
61.17, 21.481, 14.87. HRMS (EI+): m/z calcd for
C13H14N2O2 [M+]: 230.1055; found: 230.1058.
Synlett 2011, No. 8, 1137–1142 © Thieme Stuttgart · New York