Synlett 2013; 24(11): 1448-1454
DOI: 10.1055/s-0033-1338703
letter
© Georg Thieme Verlag Stuttgart · New York

Direct Amination of Phenols under Metal-Free Conditions

Jianzhong Yu
a   Department of Chemistry, Zhejiang University, Hangzhou 310027, P. R. of China   Fax: +86(571)87951895   eMail: wujunwu@zju.edu.cn
,
Yongtao Wang
a   Department of Chemistry, Zhejiang University, Hangzhou 310027, P. R. of China   Fax: +86(571)87951895   eMail: wujunwu@zju.edu.cn
,
Peizhi Zhang
b   School of Biological and Chemical Engineering, Zhejiang University of Science and Technology, Hangzhou 310012, P. R. of China
,
Jun Wu*
a   Department of Chemistry, Zhejiang University, Hangzhou 310027, P. R. of China   Fax: +86(571)87951895   eMail: wujunwu@zju.edu.cn
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Publikationsverlauf

Received: 16. März 2013

Accepted after revision: 11. April 2013

Publikationsdatum:
17. Mai 2013 (online)


Abstract

Herein, we disclose the metal-free synthesis of arylamines via the direct amination of phenols using aminating reagents. This reaction procedure uses easy accessible aminating reagents and provides a versatile synthetic route to a broad range of arylamines with various functionalities in good to excellent yield. By using a two-step route of amination and oxidative coupling reaction, we synthesized three naturally occurring carbazole alkaloids: murrayafoline A, mukonine, and clausenine from two commercially available phenols.

Supporting Information

 
  • References and Notes

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  • 21 General Procedure for the Synthesis of Amination Agents 7 and 8 A solution of 2-bromopropanoic acid (3.03 g, 20 mmol) in SOCl2 (15 mL) was heated at reflux for 3 h. After removal of the excess SOCl2 under vacuum, the resultant 2-bromopropanoyl chloride was used without further purification. 2-Bromopropanoyl chloride (20 mmol) was slowly added dropwise to a mixture of RNH2 (20 mmol) and Et3N (2.22 g, 22 mmol) in anhyd CH2Cl2 (30 mL) at 0 °C. The reaction mixture was warmed to r.t. and stirred for an additional 20 h. A solution of 1 M HCl (30 mL) was added, and the mixture was stirred for 10 min. The organic phase was separated, and the aqueous layer was extracted with CH2Cl2 (2 × 30 mL). The combined organic extracts were washed with H2O (40 mL) and brine (40 mL) and then dried over MgSO4, filtered, and concentrated in vacuo to give the product. Recrystallization from 95% EtOH gave the pure product. 2-Bromo-N-(furan-2-ylmethyl)propanamide (8d) White solid, yield 79%; mp 121–122 °C. 1H NMR (400 MHz, CDCl3): δ = 7.34–7.35 (m, 1 H), 6.82 (br s, 1 H), 6.30–6.32 (m, 1 H), 6.23–6.24 (m, 1 H), 4.39–4.44 (m, 3 H), 1.85 (d, J = 7.2 Hz, 3 H). 13C NMR (100 MHz, CDCl3): δ = 169.2, 150.5, 142.4, 110.5, 107.7, 44.7, 37.2, 22.9 ppm. HRMS (EI): m/z calcd for C8H10BrNO2 [M]+: 230.9895; found: 230.9904.
  • 22 The Procedure for the Synthesis of Amination Agent 10 A solution of 2-bromopropanoic acid (3.03 g, 20 mmol,) in SOCl2 (15 mL) was heated at reflux for 3 h. After removal of the excess SOCl2 under vacuum, the residue was added slowly to a cold solution of aq NH4OH and stirred for 2 h. The resulting white precipitate is collected by filtration to give 10 as a white crystalline powder. 2-Bromopropanamide (10)25 White solid, yield 84%; mp 79–81 °C. 1H NMR (400 MHz, CDCl3): δ = 6.36 (br s, 2 H), 4.39 (q, J = 7.2 Hz, 1 H), 1.87 (d, J = 7.2 Hz, 3 H). 13C NMR (100 MHz, CDCl3): δ = 172.2, 43.9, 22.9 ppm.
  • 23 General Procedure for the Synthesis of Diarylamines and Alkylarylamines A mixture of phenols (1.0 mmol), KOH (56 mg, 1.0 mmol), and aminating reagent 7 (1.05 mmol or 1.05 mmol aminating reagent 8) in DMSO (3 mL) was stirred at 50 °C for 2 h. After the reaction period, 62 mg (1.1 mmol) of KOH was added, and the mixture was heated at 130 °C for 2–12 h. Sat. brine was added to the solution and cooled slowly to r.t. The aqueous phase was extracted with CH2Cl2 three times. The combined organic layers were washed with three portions of sat. brine and then dried over MgSO4 and filtered. Solvent was removed under reduced pressure. The crude product was purified through column chromatography on 300–400 mesh silica gel with PE–EtOAc as eluent. 4-Bromo-N-(p-tolyl)aniline (3d) White solid, yield 93%; mp 95–96 °C. 1H NMR (400 MHz, CDCl3): δ = 7.32 (d, J = 8.4 Hz, 2 H), 7.11 (d, J = 8.0 Hz, 2 H), 6.99 (d, J = 8.0 Hz, 2 H), 6.87 (d, J = 8.4 Hz, 2 H), 5.59 (br s, 1 H), 2.33 (s, 3 H). 13C NMR (100 MHz, CDCl3): δ = 143.1, 139.5 131.9, 131.6 129.9, 119.3, 117.9, 111.7, 20.6 ppm. HRMS (EI): m/z calcd for C13H12BrN [M]+: 261.0153; found: 261.0156.
  • 24 General Procedure for the Synthesis of Carbazoles20 A test tube with a magnetic stirring bar was charged with diarylamines (0.5 mmol), Pd(OAc)2 (5 mol%), K2CO3 (10 mol%), and pivalic acid (450 mg). The uncapped test tube is placed in an oil bath, and the mixture is stirred under air at at 110 °C for 16 h. The solution is then cooled to r.t., diluted with CH2Cl2, washed with a sat. aq solution of Na2CO3, dried over MgSO4, filtered, and evaporated under reduced pressure. The crude product is purified by silica gel column chromatography to afford the corresponding coupling product.
  • 25 Oakes FT, Leonard NJ. J. Org. Chem. 1985; 50: 4986