1-Isopropylpiperazine → 5-(4-Isopropyl-piperazine-1-carbonyl)-1H-indole-2-carboxylic acid ethyl ester

Participants

Reaction Steps

To a solution of 5.0 g (21.4 mmol) 1H-indole-2,5-dicarboxylic acid 2-ethyl ester (prepared according to J. Org. Chem. 1953, 18, 345-57) in 50 mL N,N-dimethylformamide, were added 8.6 g (26.8 mmol) O-(benzotriazol-1-yl)-N,N,N′,N′-tetramethyluronium tetrafluoroborate. After 10 min., 3.44 g (26.8 mmol) 1-isopropylpiperazine and 18.3 mL (13.9 g, 107.4 mmol) N,N-diisopropylethylamine were added. After 45 min. the reaction mixture was poured into saturated aqueous sodium bicarbonate solution and extracted three times with ethyl acetate. The combined organic layers were washed three times with water, brine, dried over magnesium sulfate, filtered and evaporated. The residue was flash-chromatographed on silica gel with dichloromethane:methanol:ammonia (9:1:0.1 v/v) and ethyl acetate:methanol (9:1) as eluant to give 5.5 g (74%) of the desired compound as a light yellow solid. MS (ISP): 344.3 (M+H)+.

Provenance & Evidence