Trimethyl borate → 4-(tert-Butyldimethylsilyloxy)phenylboronic Acid (contains varying amounts of Anhydride)

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A dry reactor equipped with two addition funnels, nitrogen inlet, and a mechanical stirrer was set up over a dry ice bath. To one of the addition funnels was added a filtered, preformed Grignard reagent from the reaction of 4-(t-butyldimethylsilyloxy)-bromobenzene (28.7 g, 0.1 mol) with magnesium turnings (2.96 g, 0.12 mol) in THF (70 mL). To the other addition funnel was added trimethylborate (12.48 g, 0.12 mol) in THF (50 mL). The reactor was charged with about 10 mL of the borate solution and was cooled to -70° C. About 10 mL of the Grignard solution was then added. The remaining borate and Grignard solutions were then added in aliquots in such a way as to ensure a slight excess of borate. The reaction mixture was stirred at -70° C. for one hour then stirred at room temperature for 20 hours. The reactor was cooled to 0° C. and water (100 mL) was slowly added with vigorous stirring. The mixture was extracted with ether (400 mL). The ether layer was washed with water (2×200 mL), dried over anhydrous MgSO4, then concentrated on a roto-evaporator to afford a light-tan-colored solid (22.0 g, 87 percent). 1H and 13C NMR spectra were consistent with the following structure. ##STR11##

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