Isatin → Indole

Participants

Reaction Conditions

Reaction Steps

The corresponding isatin 1a-1d (10 mmol) was dissolved in a mixture of ethanol/pyridine/acetic acid (50 ml, 15:5:2), ethyl potassium malonate (1.87 g, 11 mmol) was added and the mixture was heated under reflux in accordance with the times stated in the table. The course of the reaction was monitored by means of TLC (eluent: ethyl acetate/hexane 1:1). For working up, the solvent mixture was distilled off in vacuo. The residue was taken up in ethyl acetate (50 ml) and the mixture was extracted by shaking with water (50 ml). After separation of the phases, the aqueous phase was extracted twice with ethyl acetate (30 ml each time). The combined organic phases were washed with 2N HCl (50 ml), dried over Na2SO4 and concentrated to 20 ml in vacuo. Hexane was added to the solution until crystallization of the corresponding 3-hydroxy-2-oxo-2,3-dihydro-1H-indol-3-yl)acetic acid ethyl ester (2a-2d) started. To bring the crystallization to completion, the mixture was cooled to 10° C. for 12 h. The solid was filtered off with suction and dried in vacuo.

Provenance & Evidence