[Synthesis]
General procedure for the synthesis of (2-(methoxycarbonyl)-1H-indol-5-yl)boronic acid from methyl 5-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-1H-indole-2-carboxylate and diethanolamine:
1. 391.2 mg (1.3 mmol) of methyl 5-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-1H-indole-2-carboxylate was dissolved in ethyl acetate (EtOAc).
2. 0.25 mL (2.6 mmol) of diethanolamine was added to the solution and the reaction mixture was stirred overnight at room temperature.
3. Upon completion of the reaction, the white precipitate formed was collected by filtration.
4. The white precipitate was sonicated in 1N hydrochloric acid (HCl).
5. The treated white precipitate was again collected by filtration and dissolved in methanol (MeOH).
6. The methanol solution was concentrated in vacuum to afford the target product (2-(methoxycarbonyl)-1H-indol-5-yl)boronic acid with a recovery of 36.6 mg (13% yield).
Product Characterization:
HPLC retention time (Rf) = 13.912 min.
1H NMR (DMSO-d6, δ): 3.85 (s, 3H), 7.15 (s, 1H), 7.36 (d, J = 8.4 Hz, 1H), 7.67 (d, J = 8.4 Hz, 1H), 7.87 (s, 1H), 8.14 (s, 1H), 11.91 (s, 1H). |