Br[C:2]1[CH:3]=[C:4]([N:8]2[CH2:13][CH2:12][N:11]([C:14]([O:16][C:17]([CH3:20])([CH3:19])[CH3:18])=[O:15])[CH2:10][CH2:9]2)[CH:5]=[CH:6][CH:7]=1.[Li]CCCC.[B:26](OC(C)C)([O:31]C(C)C)[O:27]C(C)C.P(=O)(O)(O)O>C1(C)C=CC=CC=1.O1CCCC1>[C:17]([O:16][C:14]([N:11]1[CH2:12][CH2:13][N:8]([C:4]2[CH:3]=[C:2]([B:26]([OH:31])[OH:27])[CH:7]=[CH:6][CH:5]=2)[CH2:9][CH2:10]1)=[O:15])([CH3:20])([CH3:19])[CH3:18]Into a 250-mL 3-necked round-bottom flask purged and maintained with an inert atmosphere of nitrogen, was placed a solution of tert-butyl 4-(3-bromophenyl)piperazine-1-carboxylate (3.8 g, 11.14 mmol, 1.00 equiv) in toluene/tetrahydrofuran=1:1 (40 mL). This was followed by the addition of n-BuLi (4.9 mL, 2.5M/L) dropwise with stirring at −70° C. The resulting solution was stirred for 30 min at −70° C. To this was added triisopropyl borate (2.5 g, 13.30 mmol, 1.19 equiv) dropwise with stirring at −70° C. The mixture was warmed to 0° C., the reaction was then quenched by the addition of 13 mL of saturated ammonium chloride and 3.4 mL of water. Phosphoric acid (85 wt %, 1.5 g, 1.2 equiv) was added and the mixture was stirred for 30 min. The organic layer was separated and dried over anhydrous sodium sulfate and concentrated under vacuum. The residue was dissolved in 20 mL of toluene. The product was precipitated by the addition of 80 mL of heptane. The solids were washed with 20 mL of heptane and collected by filtration. This resulted in 2.9 g (85%) of 3-(4-(tert-butoxycarbonyl)piperazin-1-yl)phenylboronic acid as a white solid.
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