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Synlett 2006(13): 2094-2098  
DOI: 10.1055/s-2006-947364
LETTER
© Georg Thieme Verlag Stuttgart · New York

An Environmentally Benign Procedure for the Synthesis of Aryl and Arylvinyl Nitriles Assisted by Microwave in Ionic Liquid

Lian-Hua Lia, Zhen-Liang Pana, Xin-Hua Duana, Yong-Min Liang*a,b
a State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000, P. R. of China
b Lanzhou Institute of Chemical Physics, Chinese Academy of Science, Lanzhou 730000, P. R. of China
Fax: +86(931)8912582; e-Mail: liangym@lzu.edu.cn;
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Publication History

Received 5 April 2006
Publication Date:
12 July 2006 (online)

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Abstract

Aryl and arylvinyl nitriles have been prepared in good yields from the corresponding bromides with potassium hexacyanoferrate(II) using palladium-catalyzed reactions in ionic liquid under microwave irradiation.

Key words

palladium - potassium hexacyanoferrate(II) - microwave - ionic liquid

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As the ionic liquid, [BMIm]BF4 was chosen because it was not only most easily manipulated at r.t., but one can be sure to be able to separate the product from the solvent completely via simple extraction with a conventional organic solvent and reused.

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K4[Fe(CN)6]·3H2O is ground to a fine powder and dried under vacuum (ca. 2 mbar) at 80 °C overnight.

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Microwave experiments were conducted using a CEM Discover Synthesis Unit (CEM Corp., Matthews, NC). The machine consists of a continuous focused microwave power delivery system with operator selectable power output from 0-300 W.

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General Procedure for the Cyanation of Aryl and Arylvinyl Bromides under Microwave Promotion.
[BMIm]BF4 (1.5 mL) was placed into a 10-mL glass microwave tube and to this was added anhyd K4[Fe(CN)6] (0.05 mmol), Na2CO3 (0.25 mmol), substrate (0.25 mmol), PdCl2 (2.5 mol%), and DMEDA (10 mol%). After sealing the tube, the mixture was exposed to microwave irradiation (a maximum microwave power of 120 W, a temperature threshold of 200 °C and a pressure threshold of 200 psi) for the requisite time. After the reaction mixture was cooled, the product was extracted from the system by washing the ionic liquid repeatedly with EtOAc-PE = 8:1 (4 × 3 mL). Finally, the product was isolated by flash chromatography on silica gel using EtOAc-PE as mobile phase.

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Compound 2a: 1H NMR (300 MHz, CDCl3): δ = 7.72-7.65 (m, 4 H), 7.60-7.56 (m, 2 H), 7.51-7.41 (m, 3 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 145.5, 139.0, 132.5, 129.0, 128.6, 127.6, 127.1, 118.9, 110.7 ppm. MS: m/z = 179 [M+], 151, 76.
Compound 2c: 1H NMR (300 MHz, CDCl3): δ = 7.81-7.78 (m, 4 H), 7.71 (d, J = 8.7 Hz, 4 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 143.4, 132.8, 127.9, 118.4, 112.3 ppm. MS: m/z = 204 [M+], 153, 126, 76.
Compound 4d: 1H NMR (300 MHz, CDCl3): δ = 8.22 (d, J = 16.5 Hz, 1 H), 8.03 (d, J = 8.1 Hz, 1 H), 7.95-7.87 (m, 2 H), 7.67-7.46 (m, 4 H), 5.96 (d, J = 16.5 Hz, 1 H) ppm.
13C NMR (75 MHz, CDCl3): δ = 147.8, 133.5, 131.5, 130.8, 130.6, 128.8, 127.3, 126.5, 125.3, 124.6, 122.7, 118.2, 98.7 ppm. MS: m/z = 179 [M+], 152, 76.