Potassium Hydroxide → ethyl 5-bromo-3,6-dimethyl-1H-indole-2-carboxylate

Participants

Reaction Steps

A solution of NaNO2 (1.52 g, 22 mmol) in water (4 mL) was added to a vigorously stirred mixture of 4-bromo-3-methylaniline (3.72 g, 20 mmol) at −5° C. After 30 min stirring, the solution was adjusted to pH 5 with NaOAc (1.40 g). A cold solution of ethyl 2-ethyl-3-oxobutanoate (4.0 g, 22 mmol) and KOH (1.36 g, 22 mmol) in EtOH (16 mL) were added followed by crushed ice (˜30 g). NaOAc was added if necessary to adjust the pH to 5. The mixture was stirred for 5 h at 0° C. then kept at this temperature overnight. The solution was extracted with EtOAc, washed with brine, dried and evaporated to 8 mL. This solution was added to a solution of HCl (25 mL, 7M in EtOH). It was further refluxed for 3 h. Upon cooling in an ice bath, water (200 mL) was added slowly. The precipitate was filtered, washed with water and dried to afford 5.36 g (91%) as a 1:1 mixture of the title compound and its ethyl 5-bromo-3,4-dimethyl-1H-indole-2-carboxylate isomer. 1H NMR (300 MHz, CDCl3), 8, mix 8.66 and 8.54 (2s, br, 1H), 7.83 and 7.23 (2s, 2×0.5H), 7.42 and 7.05 (2d, J=8.7 Hz, 2×0.5H), 4.41 (q, J=7.2 Hz, 2H), 2.81, 2.79, 2.53 and 2.49 (4s, 4×1.5H), 1.42 (t, J=7.2 Hz, 3H).

Provenance & Evidence