Diisopropylamine → (E)-5-[3-(4-Fluorophenyl)-1-isopropyl-1H-indol-2-yl]-3-oxopent-4-enoic Acid Ethyl Ester

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Reaction Conditions

Reaction Steps

1.85 ml (12.97 mmol) of diisopropylamine, dried over KOH, in 6 ml of THF, rendered absolute using sodium, are introduced into a thoroughly heated 50 ml three-necked round-bottomed flask, equipped with a magnetic stirrer, thermometer and nitrogen delivery line, and cooled to −50° C. using an ethanol/dry-ice bath. 8.1 ml (12.97 mmol) of butyllithium (1.6M in hexane) are slowly added dropwise so that the internal temperature does not exceed −40° C. Heating to from −5 to 0° C. is carried out slowly, followed by stirring at that temperature for 30 min. Cooling to −65° C. is then carried out and 1.30 ml (12.94 mmol) of ethyl acetate are slowly added dropwise so that the internal temperature does not exceed −60° C. Stirring is subsequently carried out for 40 min. at −65° C. and then 1.20 g (3.28 mmol) of (E)-3-[3-(4-fluorophenyl)-1-isopropyl-1H-indol-2-yl]-N-methoxy-N-methylacrylamide, dissolved in 5 ml of THF, are added dropwise in the course of 25 min. and stirring is carried out for one hour at that temperature. The temperature is then increased to −5° C. in the course of 15 min. and stirring is carried out for 45 min. 8 ml of saturated ammonium chloride solution are added dropwise over a period of 3 min., in the course of which the temperature rises to 12° C. Stirring is then carried out for 15 min., 10 ml of toluene are added, the phases are separated and the aqueous phase is extracted three times with 20 ml of toluene. The combined organic phases are washed with saturated sodium chloride solution until neutral, dried over magnesium sulfate, filtered and concentrated by evaporation. Purification of the crude product by means of flash chromatography (hexane/ethyl acetate=9:1) yields a viscous orange resin which, according to NMR, is the product in a keto-enol equilibrium of approximately 3:1.

Provenance & Evidence