Efficient Iron/Copper Cocatalyzed N-Arylation of Arylamines with Bromoarenes

Abstract

Fe(acac)₃ and Cu(OAc)₂×H₂O were found to effectively promote the C-N cross-coupling reaction in the presence of K₂CO₃ as the base. A series of diaryl amine with different substituents can be synthesized in moderate to good yields. This efficient and economic method is attractive for applications on an industrial scale.

catalysis - iron - copper - diaryl amine

References and Notes

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<A NAME="RW00811ST-9">9</A>

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.
4-Methyl- N -phenylaniline (3a) ^¹H NMR (400 MHz, CDCl₃): δ = 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): δ = 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-1 H -imidazole-4-carboxylate (Table 3, Entry 5)
^¹H NMR (400 MHz, CDCl₃): δ = 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): δ = 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.