suzuki reaction: Suzuki coupling of 2-(4-bromophenyl)thiophene with phenylboronic acid and 4-biphenylboronic acid are used for the preparation of 4-(2-thieny)biphenyl and 4-(2-thienyl)-1,1':4,1''-biphenyl respectively. Coupling of two equivalents of 4-(2-thienyl)phenylboronic acid with 1,4-diiodobenzene gives 4,4''-bis(2-thienyl)-1,1':4,1''-terphenyl and with 2,5-diiodothiophene, 2,5-bis[4-(2-thienyl)-phenyl]-thiophene is obtained.
The general procedure for the synthesis of 4-biphenylboronic acid from 4-bromobiphenyl was as follows: 4-bromobiphenyl (30 g, 0.12 mol) was added to a single-neck flask and the reaction was carried out under argon protection. Tetrahydrofuran (THF) (500 mL) was added and stirred at -78 °C for 10 min. Slowly n-butyllithium (2.5 M in hexane) (77 mL, 0.19 mol) was added and the mixture was stirred at -78 °C for 1 hour. Subsequently, dimethyl borate (21.9 mL, 0.19 mol) was added at -78 °C and stirring was continued at -78 °C for 30 min, then brought to room temperature and stirred for 4 hours. After completion of the reaction, extraction was carried out with distilled water and ethyl acetate (EA) and the organic layer was dried with anhydrous magnesium sulfate (MgSO4). The solvent was removed using a rotary evaporator. Finally, pure 4-biphenylboronic acid (21 g, 84% yield) was isolated by column chromatography using hexane and ethyl acetate (EA) as eluents.
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