Methyl 3-cyclohexyl-1H-indole-6-carboxylate → 1H-indole-6-carboxylic acid

Participants

Reaction Conditions

Reaction Steps

Freshly recrystallized pyridinium tribromide (recrystallization from hot AcOH (5 mL per 1 g), rinsed with cold AcOH and dried under high vacuum over KOH) was added in portions (over 10 min.) to a stirring solution of methyl 3-cyclohexyl-1H-indole-6-carboxylate (60 g, 233 mmol) (prepared using procedures describe in WO2004/065367) in CHCl3/THF (1:1, 1.25 L) at 2° C. The reaction solution was stirred at 0-5° C. for 2.5 h, and washed with sat. aq. NaHSO3 (1 L), 1 N HCl (1 L) and brine (1 L). The organic layer was dried (MgSO4) and concentrated. The resulting red oil was diluted with Et2O and concentrated. The resulting pink solid was dissolved into Et2O (200 mL) treated with hexanes (300 mL) and partially concentrated. The solids were collected by filtration and rinsed with hexanes. The mother liquor was concentrated to dryness and the procedure repeated. The solids were combined to yield 1H-indole-6-carboxylic acid, 2-bromo-3-cyclohexyl-, methyl ester (64 g, 190 mmol, 82%) as a fluffy pink solid, which was used without further purification. 1HNMR (300 MHz, CDCl3) δ 8.47 (br s, 1H), 8.03 (d, J=1.4 Hz, 1H), 7.74 (dd, J=1.4, 8.8 Hz, 1H), 7.69 (d, J=8.8 Hz, 1H), 3.92 (s, 3H), 2.82 (tt, J=3.7, 11.7 Hz, 1H), 1.98-1.72 (m, 7H), 1.50-1.27 (m, 3H). 13CNMR (75 MHz, CDCl3) δ 168.2, 135.6, 130.2, 123.1, 120.8, 120.3, 118.7, 112.8, 110.7, 52.1, 37.0, 32.2(2), 27.0(2), 26.1. LCMS: m/e 334 (M−H)−, ret time 3.34 min, column A, 4 minute gradient.

Provenance & Evidence