736990-02-6

A dioxane solution (30 mL) of Pd(dba)2 (275 mg, 0.30 mmol) and tricyclohexylphosphine (504 mg, 1.80 mmol) was added to a stirring mixture of ethyl 5-bromoindole-2-carboxylate (6.0 g, 22.4 mmol) under argon protection. KOAc (3.3 g, 33.6 mmol), bis(pinacolato)diboron (6.3 g, 24.6 mmol), and additional dioxane (20 mL) were subsequently added. The reaction mixture was stirred at 80 °C for 3 h, after which it was cooled to room temperature and filtered through diatomaceous earth. The solids were washed with EtOAc, the filtrates were combined and concentrated and finally purified by column chromatography to afford the target product 2-ethoxycarbonylindole-5-boronic acid pinacol ester (6.8 g, 97% yield).

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[3] Journal of the American Chemical Society, 2017, vol. 139, # 24, p. 8267 - 8276
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