Carbon Dioxide → 5-chloro-6-fluoro-1H-indole-7-carboxylic acid

Participants

Reaction Conditions

Reaction Steps

35 ml of THF were cooled to −75° C. and 19.05 ml (30.5 mmol) of a 1.6M solution of n-butyllithium in hexane were added under argon. Then a solution of 2.35 g (13.7 mmol) of 5-chloro-6-fluoro-1H-indole in THF (9 ml) was added dropwise (temperature kept between −70 and −75° C.) over 15 min. After 5 additional min of stirring at this temperature a solution of 3.7 g of potassium tert-butylate in THF (15 ml) was added over period of 10 min (temperature kept between −70 and −75° C.). The resulting brown solution was then stirred for 2 hours at the same temperature and treated with a large excess of solid CO2. The temperature was then raised to 10° C. over a period of 75 min and water (30 ml) was added to the reaction mixture. After separation of the organic layer, the aqueous layer was extracted with ether and treated with concentrated HCl to adjust the pH to 1. The resulting suspension was then filtered and the solid was washed with water and dried in high vacuo. The remaining residue was suspended in 10 ml of hexane/ether 9:1 and stirred for 15 min, filtered off, washed with 5 ml of the same solvent mixture and was dried in high vacuo, leading to 2.2 g of 5-chloro-6-fluoro-1H-indole-7-carboxylic acid as a light brown solid (75%). MS: 212.2 (M−H)−

Provenance & Evidence