2-(ethoxycarbonyl)-1-tosyl-1H-indole-5-carboxylic acid → 1-(toluene-4-sulfonyl)-1H-indole-2,5-dicarboxylic acid 5-tert-butyl ester 2-ethyl ester

Participants

Reaction Conditions

Reaction Steps

1-(Toluene-4-sulfonyl)-1H-indole-2,5-dicarboxylic acid 2-ethyl ester (690 mg, 1.85 mmol) was dissolved in N,N-dimethylformamide di-tert-butyl acetal (3.0 ml), and stirred at 80° C. for two and half hours. N,N-dimethylformamide di-tert-butyl acetal (2.0 ml) was further added thereto and stirred at 80° C. for three hours. After cooling to room temperature, the reaction mixture was diluted with ethyl acetate (150 ml) and water (75 ml). The organic layer was isolated, washed with water and a saturated aqueous solution of sodium chloride, and then dried over anhydrous sodium sulfate. The desiccant was removed by filtration. The filtrate was concentrated under reduced pressure. The resulting residue was purified by silica gel column chromatography (hexane/ethyl acetate=25/1 to 5/1) to give 1-(toluene-4-sulfonyl)-1H-indole-2,5-dicarboxylic acid 5-tert-butyl ester 2-ethyl ester (551 mg, 69%).

Provenance & Evidence