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Synthesis 2009(1): 138-142  
DOI: 10.1055/s-0028-1083262
PAPER
© Georg Thieme Verlag Stuttgart ˙ New York

Double Couplings of Dibromothiophenes Using Boronic Acids and Boronates

Samantha Varello, Scott T. Handy*
Department of Chemistry, Middle Tennessee State University, Murfreesboro, TN 37129, USA
Fax: +1(615)8985182; e-Mail: shandy@mtsu.edu;
Further Information

Publication History

Received 17 October 2008
Publication Date:
12 December 2008 (online)

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Abstract

One-pot double couplings of dibromothiophenes have been investigated. Standard Suzuki couplings work well for 2,4-dibromothiophene, but are much more sensitive to steric effects in the case of 2,3-dibromothiophene. By using the recently reported potassium borates, though, good yields for both dibromothiophene isomers can be achieved.

Key words

Suzuki couplings - regioselectivity - heteroaromatics - thiophenes - cross-coupling reactions - palladium catalysis

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9

These monocoupled thiophene products were used to confirm the regioselectivity of the first coupling by hydrodehalogenation of the remaining bromide and then comparison with reported spectral data for the monoarylated thiophenes.

10

EtOH-toluene afforded poor conversions, while aqueous dioxane was almost as efficient as DMF. In terms of base, K2CO3 and K3PO4 afforded slightly lower (5-10%) yields.

12

The boronate salts were prepared as described in reference 11 starting from the commercially available boronic acids with the exception of the o-methoxyphenyl boronate salt, which was prepared via the organolithium route also described in reference 11.

13

The use of CH2Cl2-hexane mixtures for chromatography was important as attempts to use EtOAc-hexanes or Et2O-hexanes mixtures resulted in much lower isolated yields due to limited product solubility in these solvents.