Phosphoric Acid → (3-[4-(Tert-butoxycarbonyl)piperazin-1-YL]phenyl)boronic acid

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To the 4-tert-Butyloxycarbonyl-1-(3-bromophenyl)piperazine from Step 1 (118.30 g, 346.9 mmol) in tetrahydrofuran/toluene (1/1, 1.5 L) at −78° C. under nitrogen was added n-butyllithium (2.5M, 160 mL, 398.9 mmol) dropwise and the resulting reaction mixture was stirred at −78° C. for 20 minutes. Triisopropyl borate (96.4 mL, 416.3 mmol) was added dropwise and the reaction was warmed to 0° C. and stirred for 2 hours. Aqueous saturated ammonium chloride (400 mL), water (100 mL) and 1 equivalent of H3PO4 (20 mL) were added and the mixture was stirred for 15 minutes and then concentrated to a volume of approximately 200 mL (at which stage the mixture became bluish and a precipitate formed). The mixture was slowly diluted with heptane (800 mL) and the resulting suspension was stirred overnight. The suspension was filtered, the solid was washed with heptane and dried to afford the title boronic acid.

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