Synthesis
The general procedure for the synthesis of 1-Boc-4-bromoindole from 4-bromoindole and di-tert-butyl dicarbonate was as follows: di-tert-butyl dicarbonate (17 g, 76.5 mmol) was slowly added to tetrahydrofuran (THF, 120 mL) containing 4-bromoindole (10 g, 51 mmol) and 4-dimethylaminopyridine (DMAP, 0.62 g, 0.51 mmol) solution. The reaction mixture was stirred at room temperature for 15 min before the solvent was removed by rotary evaporation. The residual oil was dissolved in ether and extracted by partitioning with deionized water. The separated ether layer was washed sequentially with saturated sodium bicarbonate solution (3 x 50 mL) and brine (1 x 75 mL). The washed ether layer was dried with anhydrous magnesium sulfate, filtered and the solvent was again removed by rotary evaporation. The resulting brown oil was purified by silica gel column chromatography with the eluent ethyl acetate:hexane (1:100, v/v) to give 15 g (100% yield) of tert-butyl 4-bromo-indole-1-carboxylate (1-Boc-4-bromoindole).
References
[1] Patent: US2004/72844, 2004, A1. Location in patent: Page/Page column 13-14
[2] Patent: CN107973780, 2018, A. Location in patent: Paragraph 0233; 0234; 0235; 0236
[3] Tetrahedron, 2009, vol. 65, # 34, p. 6877 - 6881
[4] Journal of Medicinal Chemistry, 2015, vol. 58, # 23, p. 9179 - 9195
[5] Tetrahedron Letters, 2017, vol. 58, # 15, p. 1499 - 1500
