[NH:1]1[C:9]2[C:4](=[CH:5][CH:6]=[CH:7][CH:8]=2)[CH:3]=[CH:2]1.[Li]CCCC.[B:15](OC(C)C)([O:20]C(C)C)[O:16]C(C)C.Cl.C([O-])(O)=O.[Na+]>C1COCC1>[NH:1]1[C:9]2[C:4](=[CH:5][CH:6]=[CH:7][CH:8]=2)[CH:3]=[C:2]1[B:15]([OH:20])[OH:16]To the SEM-protected indole prepared in step 1 (0.99 g, 4.0 mmol) in THF (10 mL) at −40° C. was added n-BuLi (2.5 M in hexanes, 1.9 mL, 4.8 mmol). The mixture was stirred at −40° C. for 1 h and then triisopropyl borate (1.2 mL, 5.2 mmol) was added. The mixture was allowed to warm to room temperature while stirring for 18 h. To the reaction mixture was added 1N HCl (aq). The mixture was stirred at room temperature for 30 minutes. The mixture was then adjusted to pH˜5 using saturated NaHCO3 (aq) The mixture was extracted with ether. The combined ether extracts were washed with water and brine, dried (Na2SO4), filtered, and concentrated in vacuo. The residue was purified by silica gel chromatography (0-50% EtOAc/hex over 30 minutes) to provide the indole boronic acid (0.20 g, 17%).
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