Pyrrolidine → 1-Benzenesulfonyl-7-fluoro-3-(5-pyrrolidin-1-ylmethyl-thiophen-2-yl)-indole

To the crude 5-(1-benzenesulfonyl-7-fluoroindol-3-yl)-thiophene-2-carboxaldehyde was sequentially added 4 Å molecular sieves (1 g), pyrrolidine (0.44 ml, 5.36 mmol), sodium cyanoborohydride (0.034 g, 0.54 mmol) and glacial acetic acid (1 drop). The resulting mixture was then stirred at room temperature for 18 h, filtered and the filter cake washed with methanol (2×30 ml) and dichloromethane (2×30 ml). The combined filtrate was concentrated in vacuo, dissolved in dichloromethane (20 ml), washed with aqueous sodium hydroxide (2M; 15 ml), dried with sodium sulphate and concentrated in vacuo. The residue was then purified by flash column chromatography eluting with 0-10% (v/v) methanol in dichloromethane to afford 1-benzenesulfonyl-7-fluoro-3-(5-pyrrolidin-1-ylmethyl-thiophen-2-yl)-indole as a yellow oil (0.22 g, 0.46 mmol).