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Synlett 2008(18): 2888-2892  
DOI: 10.1055/s-0028-1083568
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Copper(II) Acetate Catalyzed Cross-Coupling of Pentafluorophenylboronic Acid with Amines under an Atmosphere of Oxygen

Weihui Zhong, Zhenyu Liu, Chuanming Yu, Weike Su*
Key Laboratory of Pharmaceutical Engineering of Ministry of Education, College of Pharmaceutical Sciences, Zhejiang University of Technology, Hangzhou 310014, P. R. of China
Fax: +86(571)88320752; e-Mail: suweike@zjut.edu.cn;
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Publication History

Received 15 July 2008
Publication Date:
16 October 2008 (online)

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Abstract

Under an atmosphere of oxygen and a catalytic amount of Cu(OAc)2, pentafluorophenylboronic acid reacted with anilines at room temperature to produce the corresponding N-pentafluoro­phenylanilines in moderate to good yields. In the case of alkyl­amines, unexpected N-alkyl-2,2′,3,3′,4′,5,5′,6,6′-nona-fluoro-biphenyl-4-amines were formed under the similar conditions in moderate yields.

Key words

copper acetate - pentafluorophenylboronic acid - amines - N-pentafluorophenylanilines - cross-coupling

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Typical Procedure for the Preparation of Compound 3b
Copper(II) acetate (0.2 mmol) was added to a stirred mixture of EtOAc (15 mL) and pentafluorophenylboronic acid (1.5 mmol). The mixture was stirred for 10 min at r.t. then the 4-chlorophenylamine (1.0 mmol) was slowly added to the mixture. The reaction mixture was stirred sequentially for 5 h under the atmosphere of oxygen. The reaction was monitored by TLC and quenched with H2O (5 mL). The resulting mixture was filtrated through a pad of Celite and the filtrate was extracted with EtOAc (3 × 15 mL). The combined organic layers were dried over Na2SO4, filtered, and concentrated under reduced pressure to give a crude product, which was purified by column chromatography to give N-(4-chlorophenyl)-2,3,4,5,6-pentafluoroaniline (3b). Light yellow crystals; mp 78.5-79.8 ˚C. IR (KBr): 3417, 3133, 1524, 1495, 1399 cm-¹. ¹H NMR (500 MHz, CDCl3): δ = 5.39 (br, 1 H), 6.75 (d, 2 H, J = 7.5 Hz), 7.23 (d, 2 H, J = 7.0 Hz). ¹³C NMR [100 MHz, CDCl3 (except for C6F5)]: δ = 117.7 (2 × CH), 126.9, 129.2 (2 × CH), 140.7. ¹9F NMR (376 MHz, CDCl3): δ = -158.98 (t, 1 F, J = 21.4 Hz),
-158.57 (dd, 2 F, J 1 = 21.4 Hz, J 2 = 21.4 Hz), -145.46 (d, 2 F, J = 19.6 Hz). MS (EI): m/z (%) = 293 (8) [M+], 273 (4), 238 (8), 151 (100), 88 (38). HRMS (EI): m/z calcd for C12H5ClF5N: 293.0031; found: 293.0030.

15

Typical Procedure for the Preparation of Compound 7a
Copper(II) acetate (1 mmol) was added to a stirred mixture of DMF (25 mL) and pentafluorophenylboronic acid (2 mmol). The mixture was stirred for 10 min at r.t. then the Et2NH (1.0 mmol) were slowly added to the mixture. The reaction mixture was stirred sequentially for 12 h under the atmosphere of oxygen. The reaction was monitored by TLC and quenched with H2O (5 mL). The resulting mixture was filtrated through a pad of Celite, and the filtrate was extracted with EtOAc (3 × 15 mL). The combined organic layers were dried over Na2SO4, filtered, and concentrated under reduced pressure to give a crude product, which was purified by column chromatography to give N,N-diethyl-2,2′,3,3′,4′,5,5′,6,6′-nonafluorobiphenyl-4-amine (7a). Light yellow crystal; mp 71.6-72.5 ˚C. IR (KBr): 2976, 2917, 1644, 1503, 1384, 1046 cm-¹. ¹H NMR (400 MHz, CDCl3): δ = 1.16 (t, 6 H, J = 7.2 Hz), 3.33 (q, 4 H, J = 7.2 Hz). ¹³C NMR [100 MHz, CDCl3 (except for C12F9)]: δ = 13.4 (2 × CH), 46.8 (2 × CH). ¹9F NMR (376 MHz, CDCl3): δ = -157.56 to -157.43 (m, 2 F), -147.96 (t, 1 F, J = 21.4 Hz), -145.62 to -145.568 (m, 2 F), -137.16 to
-137.09 (m, 2 F), -133.91 to -133.83 (m, 2 F). MS (EI): m/z (%) = 387 (25) [M+], 358 (15), 372 (100), 344 (75). HRMS (EI): m/z calcd for C16H10F9N: 387.0670; found: 387.0672.