[C:1](C1NC2C(C=1)=CC=CC=2)([O:3][C:4]([CH3:7])([CH3:6])[CH3:5])=[O:2].C(O[B:21]([O-:23])[O-:22])(C)C.[Li+].C[CH:26]([N-:28][CH:29]([CH3:31])[CH3:30])[CH3:27].Cl.[CH2:33]1[CH2:37][O:36][CH2:35][CH2:34]1>>[C:1]([N:28]1[C:29]2[C:30](=[CH:33][CH:34]=[C:35]([O:36][CH3:37])[CH:31]=2)[CH:27]=[C:26]1[B:21]([OH:22])[OH:23])([O:3][C:4]([CH3:5])([CH3:6])[CH3:7])=[O:2]The above Boc-indole (3.08 g, 12.5 mmol) and isopropylborate (4.83 mL, 21.9 mmol) are dissolved in anhydrous THF (20 mL) and the solution is cooled at 0° C. While stirring, LDA (12.5 mL, 1.5 M mono-THF complex in cyclohexane, 18.7 mmol) is added dropwise. The mixture is stirred at 0° C. for 15 min and then room temperature for 0.5 h, followed by the addition of HCl (6 N, 3.0 mL, 18 mmol) in an ice-water bath. The organic solvent is removed in vacuo and the residue is suspended in H2O (100 mL) and acidified with HCl (6 N) to pH 4˜5. The precipitate is collected via filtration and washed with water and hexanes and dried in air to provide 1-Boc-6-methoxyindole-2-boronic acid (3.38 g, 93%).
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