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Synlett 2010(6): 909-912  
DOI: 10.1055/s-0029-1219380
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

First Site-Selective Suzuki-Miyaura Reactions of 2,3,4-Tribromothiophene

Serge-Mithérand Tengho Toguema, Alexander Villingera, Peter Langer*a,b
a Institut für Chemie, Universität Rostock, Albert Einstein Str. 3a, 18059 Rostock, Germany
b Leibniz-Institut für Katalyse an der Universität Rostock e.V., Albert Einstein Str. 29a, 18059 Rostock, Germany
Fax: +1(381)4986412; e-Mail: peter.langer@uni-rostock.de;
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Publication History

Received 5 December 2009
Publication Date:
08 February 2010 (online)

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Abstract

The first Suzuki-Miyaura reactions of 2,3,4-tribromothiophene are reported. These reactions provide a convenient and site-selective approach to 2-aryl-3,4-dibromothiophenes, 2,4-diaryl-3-bromothiophenes, and 2,3,4-triarylthiophenes.

Key words

catalysis - palladium - Suzuki-Miyaura reaction - site ­selectivity - thiophene

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General Procedure for the Synthesis of 2-Aryl-3,4-dibromothiophenes 2
To a mixture of 1 (0.159 g, 0.5 mmol), arylboronic acid (0.55 mmol), Pd(PPh3)4 (5 mol%) were added a mixture of 1,4-dioxane and toluene (1:1, 5 mL) and an aq solution of K2CO3 (2 mL, 2 M) under argon atmosphere. The reaction mixture was stirred at 100 ˚C for 5 h and was subsequently allowed to cool to 20 ˚C. The solution was poured into H2O and CH2Cl2 (25 mL each), and the organic and the aqueous layer were separated. The latter was extracted with CH2Cl2 (3 × 25 mL), dried (Na2SO4), filtered, and concentrated in vacuo. The residue was purified by flash column chromatography (flash silica gel, heptanes).
Synthesis of 3,4-Dibromo-2-(4-ethylphenyl)thio-phene (2b)
Starting with 1 (0.320 g, 1.0 mmol) and 4-ethylphenyl- boronic acid (0.165 g, 1.1 mmol), 2b was isolated (0.298 g, 87%) as a colorless oil. ¹H NMR (300 Hz, CDCl3): δ = 1.32 (t, ³ J = 7.6 Hz, 3 H, CH3), 2.75 (q, ³ J = 7.6 Hz, 2 H, CH2), 7.32 (d, ³ J = 8.4 Hz, 2 H, Ar), 7.38 (s, 1 H, Ar), 7.58 (d, ³ J = 8.3 Hz, 2 H, Ar). ¹³C NMR (62 MHz, CDCl3): δ = 15.4 (CH3), 28.7 (CH2), 111.0, 114.7 (CBr), 122.0 (CH, thiophene), 128.2 (2 CH, Ar), 128.9 (2 CH, Ar), 130.3, 139.7, 145.7 (C). IR (KBr): ν = 3107 (w), 3020 (w), 2961 (m), 2927 (m), 2630 (w), 2306 (w), 1903 (w), 1524 (w), 1484 (m), 1308 (w), 1126 (w), 963 (w), 877 (s), 828 (s), 785 (m), 722 (s), 645 (w), 585 (m), 539 (m) cm-¹. GC-MS (EI, 70 eV): m/z (%) = 348 (44) [M+, 8¹Br, 8¹Br], 346 (83) [M+, 8¹Br, 79Br], 344 (41) [M+, 79Br, 79Br], 333 (54), 331 (100) [M+], 329 (50), 186 (11), 171 (38), 139 (11). HRMS (EI, 70 eV): m/z calcd for C12H10Br2S [M+, Br, 8¹Br]: 345.88440; found: 345.88457.

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