Hydrochloric Acid → (4-(Benzo[d]oxazol-2-yl)phenyl)boronic acid

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First, 5.5 g (20 mmol) of 2-(4-bromophenyl)benzoxazole was put into a 300 mL three-neck flask and the atmosphere in the flask was substituted by nitrogen. 120 mL of THF was added and cooled to −78° C. under a nitrogen stream. After cooling, 13 mL (22 mmol) of 1.6 M n-butyllithium was dripped to this solution, and the mixture was stirred at the same temperature for 2 hours. After a certain time, 4.4 mL (40 mmol) of trimethyl borate was added to this solution, and the temperature of the solution was raised to room temperature, and then, the solution was stirred for 16 hours. After a certain time, 100 mL of 1M hydrochloric acid was added and stirred for 1 hour. An aqueous layer of the obtained mixture was extracted with ethyl acetate. The obtained extract was washed with a saturated saline together with the organic layer and then dried over magnesium sulfate. The obtained mixture was subjected to gravity filtration, and the obtained filtrate was concentrated to give a solid. The obtained solid was recrystallized with ethyl acetate/hexane, so that 3.3 g of target white powder was obtained with a yield of 69%.

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