Synthesis
The general procedure for the synthesis of 1-methylindole-5-boronic acid pinacol ester from 5-bromo-1-methyl-1H-indole and biboronic acid pinacol ester is as follows: the synthesis was carried out according to the literature method with appropriate adjustments. To an 8-dram vial equipped with a magnetic stirrer were sequentially added pinacol bis(boronic acid) ester (2 mmol, 508 mg), 5-bromo-1-methyl-1H-indole (2.1 mmol, 441 mg), [1,1'-bis(diphenylphosphino)ferrocene]palladium(II) dichloride (0.06 mmol, 44 mg), potassium acetate (6 mmol, 589 mg), and degassed 1,1'-bis(diphenylphosphino)ferrocene(III). ), and degassed 1,4-dioxane (10 mL). The reaction mixture was purged under a strong stream of nitrogen for 5 min to deoxygenate, followed by transferring the reaction system to an oil bath preheated to 80 °C with continuous stirring for 48 h. The reaction was carried out in a cooled room with a temperature range of 0.5 °F to 0.5 °F. Upon completion of the reaction, it was cooled to room temperature and the reaction mixture was filtered through a diatomaceous earth pad and washed with ethyl acetate (50 mL). The filtrates were combined and concentrated under reduced pressure to remove the solvent. The crude product was purified by fast column chromatography with petroleum ether as eluent, followed by a 5% to 12% gradient elution of ether/petroleum ether to afford 342 mg (67% yield) of the target product, 1-methylindole-5-boronic acid pinacol ester, as a white solid.
References
[1] Synlett, 2018, vol. 29, # 15, p. 2031 - 2034
[2] ACS Catalysis, 2018, vol. 8, # 5, p. 4049 - 4054
[3] Angewandte Chemie - International Edition, 2018, vol. 57, # 34, p. 10999 - 11003
[4] Angew. Chem., 2018, # 130, p. 11165 - 11169,5
[5] Patent: WO2016/180537, 2016, A1. Location in patent: Page/Page column 133
