Synthesis
In a 500-mL single-necked flask, 5-bromoindole (20.00 g, 0.1 mol), bis(pinacolato)diboron (51.80 g, 0.2 mol), potassium acetate (22.80 g, 0.2 mol), [1,1'-bis(diphenylphosphino)ferrocene]palladium dichloride (1.50 g), and 350 mL of dioxane were added in sequence. The reaction mixture was refluxed for 8 hours under nitrogen protection. After completion of the reaction, it was cooled to room temperature and the dioxane solvent was removed by rotary evaporator. Subsequently, the reaction mixture was washed with 200 ml of distilled water and extracted (3 times) with dichloromethane. The organic phases were combined and recrystallized by methanol-dichloromethane mixed solvent to give 21.8 g of 5-indoleboronic acid pinacol ester in 90% yield.
References
[1] Patent: CN105601612, 2016, A. Location in patent: Paragraph 0051; 0052; 0053
[2] Journal of Organic Chemistry, 2004, vol. 69, # 20, p. 6812 - 6820
[3] Organic Letters, 2012, vol. 14, # 2, p. 600 - 603
[4] Bioorganic and Medicinal Chemistry Letters, 2017, vol. 27, # 17, p. 4150 - 4155
[5] Patent: KR101603387, 2016, B1. Location in patent: Paragraph 0084-0088; 0143-0146
