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.

Key words

catalysis - iron - copper - diaryl amine

References and Notes

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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.
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.