Hydrochloric Acid → 6-(1H-indol-5-yl)hex-5-ene-2,4-dione

Participants

Reaction Conditions

Reaction Steps

In a 300 mL pear-shaped evaporating flask equipped with a cooling tube were placed 15.5 mL of ethyl acetate, 15.9 mL (155 mmol) of 2,4-pentanedione, and 3.24 g (46.5 mmol) of boron oxide. To the mixture under stirring at 70° C., 4.50 g (31.0 mmol) of 1H-indole-5-carboxaldehyde and a solution of 7.2 mL (31 mmol) of triisopropyl borate in ethyl acetate (31 mL) were added dropwise. The mixture was stirred at 70° C. for 30 minutes and a solution of 3.68 mL (37.2 mmol) of n-butylamine in ethyl acetate (9.3 mL) was added dropwise. After being stirred at 85° C. for 1 hour, the mixture was cooled down to 50° C., and 3 N hydrochloric acid (22 mL) was added thereto. The mixture was stirred at the same temperature for 10 minutes and neutralized with a saturated sodium bicarbonate solution. The resulting solution was diluted with ethyl acetate, washed twice with saturated brine, and dried over magnesium sulfate. After filtration, the solvent was evaporated under reduced pressure. The residue was purified by silica gel column chromatography (hexane/ethyl acetate=90/10 to 70/30) and crystallization (ethyl acetate/hexane) to give 3.46 g (49% yield) of the title compound as a yellow powder with the following properties.

Provenance & Evidence