Step 3: tert-butyl 5-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)dihydroindole-1-carboxylate (120 mg, 0.35 mmol) was dissolved in dichloromethane (5 mL), 2,2,2-trifluoroacetic acid (1 mL) was added, and the reaction mixture was stirred for 2 hours at room temperature. After the reaction was completed, it was neutralized with saturated aqueous sodium bicarbonate solution to pH=8 and then extracted with dichloromethane. The organic phases were combined, washed with brine, dried over anhydrous sodium sulfate and concentrated under reduced pressure to afford the target product 5-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)dihydroindole (74 mg, 87% yield).1H NMR (CDCl3) δ: 7.56 (1H, s), 7.50 (1H, d, J = 8.0 Hz), 6.60 (1H, d, J = 8.0 Hz), 3.57 (2H, t, J = 8.8 Hz), 3.02 (2H, t, J = 8.8 Hz), 1.32 (12H, s).
