Toluene → 2,5-Diphenyl-terephthalic acid diethylester

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To a 3 L 3-neck flask equipped with a mechanical stirrer, reflux condenser and rubber septum was added phenyl boronic acid pinacol ester 2a (128.9 g, 0.63 mol, 2 equiv.) and 2,5-dibromo-terephthalic acid diethylester 1a (120 g, 0.32 mol, 1 equiv.) as a suspension in toluene (500 mL). A further 500 mL of toluene was then added and the reaction mixture briefly stirred before degassing using a nitrogen purge for 1 hour at 40° C. After this period dichloro-bis(triphenyl phosphine) palladium (II) (0.55 g, 0.78 mmol, 1/8 mol % per bromide) was added as a dry powder. The reaction mixture was then stirred under nitrogen for 15 minutes at 40° C. before the addition of tetra-ethylammonium carbonate (790 mL, ca. 33 wt % aqueous solution, 2 equiv. per arylboronate). The reaction was then stirred at 90° C. under nitrogen overnight (ca. 16 hrs.). TLC analysis at this point (DCM, silica plates) revealed a bright fluorescent blue spot (Rf ca. 0.6) and the absence of any starting material. Once the reaction mixture had cooled the aqueous layer was extracted and the solvent removed under reduced pressure to yield a light brown solid residue which was recrystallised from methanol to give the title compound as white crystalline solid. Slow evaporation of the mother liquor provided a second crop of product (92 g total, 77%, >99% pure by GC).

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