Diethyl Ether → 2-(4-Piperazin-1-yl-benzenesulfonyl)-1H-indole

The Boc-protecting group on 0.530 g, 1.41 mmol of the 2-(4-Fluorobenzenesulfonyl)-indole-1-carboxylic acid tert-butyl ester from Step 1 was removed by stirring at room temperature in 3 mL of neat TFA. The reaction mixture turned a light burgundy color while stirring. The TFA was removed by adding 25 mL of toluene and removing the solvent/TFA as an azeotrope. This was repeated and the oily residue was then transferred to a sealed tube using 5 mL of DMSO. Solid piperazine (0.61 g, 7.06 mmol, 5 eq.) was added, the tube was sealed, and the reaction mixture heated at 100° C. (bath temp.) for a period of 16 h. The reaction mixture was allowed to cool to room temperature, diluted with 400 mL of ethyl acetate, then washed sequentially with saturated NaHCO3 solution, water, brine, and dried over anhydrous magnesium sulfate. Evaporation of the solvent gave an amber glass which was treated with anhydrous diethyl ether. Hexane (25 mL) was added to the solution, causing a small amount of solid to precipitate out of solution. The mixture cooled was to 0° C. in an ice-water bath, followed by vacuum-filtration of the off-white solid. After drying, 0.150 g, 0.44 mmol, 31.1% yield of 2-(4-Piperazin-1-yl-benzenesulfonyl)-1H-indole was obtained, with a melting point range of 246–248.5° C. and M+H of 342.