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Synlett 2009(20): 3311-3314  
DOI: 10.1055/s-0029-1218355
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Site-Selective Suzuki-Miyaura Reactions of 2,3,5-Tribromothiophene

Serge-Mithérand Tengho Toguema, Alexander Villingera, Peter Langer*a,b
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 Leibniz-Institut für Katalyse an der Universität Rostock e.V., Albert Einstein Str. 29a, 18059 Rostock, Germany
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Publication History

Received 18 September 2009
Publication Date:
11 November 2009 (online)

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Abstract

The first Suzuki-Miyaura reactions of 2,3,5-tribromothiophene are reported. These reactions provide a convenient and site-selective approach to 5-aryl-2,3-dibromothiophenes, 2,5-diaryl-3-bromothiophenes, and 2,3,5-triarylthiophenes.

Key words

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

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General Procedure for the Synthesis of 2,3-Dibromo-5-arylthiophene 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 8 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, n-heptane).
Synthesis of 2,3-Dibromo-5- p -tolylthiophene (2a)
Starting with 1 (0.320 g, 1.0 mmol) and 4-tolylboronic acid (0.149 g, 1.1 mmol), 2a was isolated (0.150 g, 47%) as a colorless solid, mp 83-85 ˚C. ¹H NMR (300 MHz, CDCl3): δ = 2.26 (s, 3 H, CH3), 6.94 (s, 1 H, Ar), 7.08 (d, ³ J = 8.0 Hz, 2 H, Ar), 7.26 (d, ³ J = 8.2 Hz, 2 H, Ar). ¹³C NMR (62 MHz, CDCl3): δ = 21.3 (CH3), 109.4, 114.5 (CBr), 125.0, 125.3, 128.7, 129.4, 129.8 (CH, Ar), 130.0, 138.6, 145.6 (C). IR (KBr): ν = 3091 (w), 3019 (w), 2918 (w), 2852 (w), 1498 (m), 1433 (w), 1118 (w), 997 (w), 821 (w), 801 (m), 550 (w) cm-¹. GC-MS (EI, 70 eV): m/z (%) = 334 [M+, 8¹Br, 8¹Br], 332 (100) [M+, 8¹Br, 79Br], 331 (16) [M+], 330 (49) [M+, 79Br, 79Br], 172 (35), 171 (30), 86 (11). HRMS (EI, 70 eV): m/z calcd for C11H8Br2S [M+, 8¹Br, 79Br]: 331.86875; found: 331.86882.

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CCDC-749926 and 749927 contain all crystallographic details of this publication and is available free of charge at www.ccdc.cam.ac.uk/conts/retrieving.html or can be ordered from the following address: Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB21EZ, UK; fax: +44 (1223)336033; or deposit@ccdc.cam.ac.uk.