4-Fluoroindole → 4-Fluoro-2,3-dihydro-1H-indole

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Reaction Steps

Sodium cyanoborohydride (1.86 g, 29.62 mmol) was added portion wise to a solution of 4-fluoro-1H-indole (2 g, 14.81 mmol) in acetic acid (20 mL) at 0° C. and stirred at ambient temperature for 2 h. The resulting mixture was concentrated in vacuo and partitioned between ethyl acetate (100 mL) and water (100 mL). The organic layer was separated and the aqueous layer was extracted with ethyl acetate (5×30 mL). The combined organic layers were then washed with water (5×20 mL), sodium bicarbonate solution (3×30 mL), brine (3×20 mL), dried over anhydrous sodium sulphate and concentrated in vacuo to give the crude product. Purification by column chromatography over neutral alumina using 5% ethyl acetate in hexane as eluent to afforded 4-fluoroindoline (1 g, 45%) as a brown liquid.

Provenance & Evidence