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Synlett 2009(12): 1941-1944  
DOI: 10.1055/s-0029-1217537
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

C-H and C-Si Functionalization of Furan Derivatives: Palladium-Catalyzed Homocoupling and Arylation Reactions

Shigeru Matsuda, Masabumi Takahashi, Daiki Monguchi, Atsunori Mori*
Department of Chemical Science and Engineering, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501, Japan
Fax: +81(78)8036181; e-Mail: amori@kobe-u.ac.jp;
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Publication History

Received 24 March 2009
Publication Date:
03 July 2009 (online)

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Abstract

Palladium-catalyzed arylation reactions of benzofuran derivatives are shown to take place at the carbon-hydrogen bond or carbon-silicon bond adjacent to the oxygen atom. A variety of furan derivatives are obtained in good yields.

Key words

C-H arylation - benzofuran - palladium - homocoupling reaction - cross-coupling reaction

7

Fractional addition of silver was shown to improve the yield of the coupling product in the reactions of thiophene derivatives.¹b,²c

10

Experimental Procedure for the Homocoupling Reaction of 1 To a 50 mL Schlenk tube equipped with a magnetic stirring bar were added PdCl2 (PhCN)2 (5.8 mg, 0.015 mmol), DMSO (3 mL), benzofuran (1, 55 µL, 0.5 mmol), and AgF (127 mg, 1.0 mmol) in one portion, and the resulting mixture was stirred at r.t. for 3 h. Additional AgF (2 × 1.0 mmol) were then added, and stirring was continued for further 3 h and 5 h, respectively. The reaction mixture was passed through a Celite pad to remove a solid residue, and the cake was washed repeatedly with Et2O. The filtrate was washed with H2O twice (2 × 50 mL) and brine (50 mL). Then, the organic layer was dried over anhyd MgSO4 and concentrated under reduced pressure to leave a crude solid, which was purified by chromatography on silica gel to afford 33 mg of 2 (56%).
2,2′-Bibenzofuran ( 2) ¹¹ Mp 202-203 ˚C. ¹H NMR (500 MHz, CDCl3): δ = 7.17 (s, 2 H), 7.25-7.37 (m, 4 H), 7.55 (d, J = 8.0 Hz, 2 H), 7.63 (d, J = 8.2 Hz, 2 H). ¹³C NMR (125 MHz, CDCl3): δ = 103.7, 111.3, 121.4, 123.3, 125.1, 128.5, 147.7, 155.1. IR (KBr): 1441, 1256, 1173, 1049, 876, 804, 750 cm-¹.
Experimental Procedure for the C-Si Arylation Reaction of 7 and 3c To a 25 mL Schlenk tube equipped with a magnetic stirring bar were added, PdCl2 (PPh3)2 (10.5 mg, 0.015 mmol), DMSO (1 mL), 2-trimethylsilylbenzofuran (7, 95 mg, 0.5 mmol), and ethyl 4-iodobenzoate (6c, 165 mg, 0.6 mmol) under argon atmosphere. The mixture was heated in an oil bath at 100 ˚C, KF (7.3 mg, 0.125 mmol), and AgNO3 (21.2 mg, 0.125 mmol) were added in one portion, and the resulting mixture was continued for 1 h. Addition of AgNO3/KF (0.125 mmol) and stirring for 1 h at 100 ˚C were repeated for further 5 times. After cooling to r.t., the mixture was passed through a Celite pad, which was washed with EtOAc repeatedly. The filtrate was washed with H2O twice. Then the organic layer was dried over anhyd MgSO4 and concentrated under reduced pressure to leave a crude solid, which was purified by chromatography on silica gel to afford 99 mg of 4 (75%).¹²