Synthesis
General procedure for the synthesis of indole-2-boronic acid pinacol ester from indole and bis-boronic acid pinacol ester: Dimethyl(1,5-cyclooctadiene)iridium(I) (64 mg, 0.096 mmol) and 4,4'-di-tert-butyl-2,2'-bipyridine (52 mg, 0.19 mmol) were added to a dry, round-bottomed flask under argon gas protection. The flask was evacuated and backfilled three times with argon. Indole (1.50 g, 12.8 mmol) and bis(pinacolato)diboron (1.62 g, 6.40 mmol) were then added and the flask was again purged with argon. Anhydrous hexane (38.5 mL) was injected and the reaction mixture was stirred for 8 hours at room temperature in an argon atmosphere. Upon completion of the reaction, the reaction mixture was concentrated under reduced pressure and the resulting residue was purified by silica gel column chromatography (eluent: 0-10% ethyl acetate/hexane) to afford indole-2-boronic acid pinacol ester (2.66 g, 85% yield). The product was characterized by 1H NMR (300 MHz, d6-DMSO): δ 11.27 (s, 1H), 7.55 (d, J = 7.9 Hz, 1H), 7.38 (dd, J = 8.2, 0.8 Hz, 1H), 7.15-7.06 (m, 1H), 7.00-6.92 (m, 1H), 6.90-6.87 (m, 1H) , 1.32 (s, 12H).
References
[1] Journal of the American Chemical Society, 2015, vol. 137, # 7, p. 2665 - 2673
[2] Patent: WO2014/22744, 2014, A1. Location in patent: Paragraph 0117
[3] Journal of the American Chemical Society, 2014, vol. 136, # 18, p. 6566 - 6569
[4] Dalton Transactions, 2015, vol. 44, # 29, p. 13007 - 13016
[5] Organic Letters, 2012, vol. 14, # 16, p. 4266 - 4269
