Hydrochloric Acid → 1H-indole-6-carboxylic acid

Participants

Reaction Conditions

Reaction Steps

An alternative procedure that can by used to provide 1H-indole-6-carboxylic acid, 2-bromo-3-cyclohexyl- is described below: A solution of methyl 2-bromo-3-cyclohexyl-1H-indole-6-carboxylate (117 g, 349 mmol) and LiOH.H2O (26.4 g, 629 mmol) in MeOH/THF/H2O (1:1:1, 1.8 L) was heated at reflux for 3 h. The reaction mixture was cooled in an ice/H2O bath to ˜2° C., and then neutralized with 1M HCl (˜650 mL) that was added at such a rate that the temperature did not exceed 5° C. On addition, the mixture was diluted with H2O (1 L) and stirred while warming to ambient temperature. The resultant precipitates were collected by filtration, rinsed with H2O and dried to yield the mono THF solvate of 1H-indole-6-carboxylic acid, 2-bromo-3-cyclohexyl- (135.5 g, 345 mmol, 99%) as a yellow solid, which was used without further purification. 1HNMR (300 MHz, CDCl3) δ 11.01 (br s, 1H), 8.77 (s, 1H), 8.07 (d, J=1.5 Hz, 1H), 7.82 (dd, J=1.5, 8.8 Hz, 1H), 7.72 (d, J=8.8 Hz, 1H), 3.84-3.74 (m, 4H), 2.89 (m, 1H), 1.98-1.72 (m, 11H), 1.50-1.24 (m, 3H). 13CNMR (75 MHz, CDCl3) δ 172.7, 135.5, 130.7, 122.3, 120.9(2), 118.8, 113.3, 111.1, 67.9(2), 37.0, 32.2(2), 27.0(2), 26.1, 25.5(2). LCMS: m/e 320 (M−H)−, ret time 2.21 min, column A, 4 minute gradient.

Provenance & Evidence