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Synlett 2006(17): 2812-2814  
DOI: 10.1055/s-2006-950271
LETTER
© Georg Thieme Verlag Stuttgart · New York

Synthesis of 2-(2-Arylethenyl)-5-arylfurans by Regioselective Palladium(0)-Catalyzed Coupling Reactions of 2-(2-Bromo-2-nitroethenyl)-5-bromofuran

Dang Thanh Tuana,b, Dang Thanh Tunga, Peter Langer*a,c
a Institut für Chemie, Universität Rostock, Albert-Einstein-Str. 3a, 18059 Rostock, Germany
Fax: +49(381)4986412; e-Mail: peter.langer@uni-rostock.de;
b Institut für Biochemie, Universität Greifswald, Soldmannstr. 16, 17487 Greifswald, Germany
c Leibniz-Institut für Katalyse e. V. an der Universität Rostock, Albert-Einstein-Str. 29a, 18059 Rostock, Germany
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Publication History

Received 23 August 2006
Publication Date:
09 October 2006 (online)

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Abstract

The Suzuki reaction of 2-(2-bromo-2-nitroethenyl)-5-bromofuran, readily available from furfural, resulted in regioselective attack onto the furan moiety. The alkenyl moiety could be functionalized in a second Suzuki reaction.

Key words

catalysis - furans - green chemistry - heterocycles - palladium - regioselectivity

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General Procedure for the Synthesis of 2-(2-Bromo-2-nitroethenyl)-5-arylfurans 4a-i.
To a toluene solution (3 mL) of 3 (0.356 g, 1.2 mmol) was added Pd(PPh3)4 (0.042 g, 3 mol%) at 20 °C. After stirring for 30 min, the arylboronic acid (1.0 mmol), K3PO4 (2.0 mmol) and H2O (0.5 mL) were added. The mixture was stirred at 90 °C for 8 h. After cooling to ambient temperature, the mixture was diluted with EtOAc, dried (Na2SO4), and filtered through a short Celite® pad. The solution was concentrated in vacuo and the residue was purified by column chromatography (silica gel, n-heptane-EtOAc = 20:1 to 5:1).
Synthesis of 2-[( Z )-2-bromo-2-nitrovinyl]-5-(4-ethoxy­-phenyl)furan (4e). Starting with 3 (0.356 g, 1.2 mmol) and (4-ethoxyphenyl)boronic acid (1.0 mmol), 4e was isolated (0.226 g, 67%) as a red solid; mp 127-128 °C. 1H NMR (300 MHz, CDCl3): δ = 1.42 (t, 3 J = 7.2 Hz, 3 H, CH3), 4.05 (q, 3 J = 7.2 Hz, 2 H, OCH 2CH3), 6.76 (d, 3 J = 3.8 Hz, 1 H, furan), 6.92 (d, 3 J = 8.7 Hz, 2 H, Ar), 7.38 (d, 3 J = 3.8 Hz, 1 H, furan), 6.92 (d, 3 J = 8.7 Hz, 2 H, Ar), 8.53 (s, CH). 13C NMR (75 MHz, CDCl3): δ = 14.8 (CH2 CH 3), 63.6 (OCH 2CH3), 107.7 (CH), 115.1, 115.1, 126.8, 126.8 (CH, Ar), 124.2, 124.6 (CH, furan), 122.2, 123.9, 145.7, 159.9, 161.1 (C). IR (KBr): 3432 (m), 3050 (m), 2971 (w), 1603 (s), 1599 (s), 1467 (s), 1280 (s), 1235 (s), 1177 (s), 1035 (s), 964 (s) cm-1. MS (EI, 70 eV): m/z (%) = 339 (30) [M+, 81Br], 337 (31) [M+, 79Br], 258 (100), 227 (10), 212 (23), 184 (37), 183 (29), 155 (17), 131 (22), 77 (8), 69 (11). HRMS (EI, 70 eV): m/z calcd for C14H12O4NBr [M+, 79Br]: 336.9944; found: 336.9939. All products gave satisfactory spectroscopic data and correct elemental analyses and/or high-resolution mass data.