In a three-neck round bottom flask equipped with argon inlet was charged with anhydrous dimethylformamide and 3-chloro-propane-1-sulfonic acid benzhydryl-amide (893 mg, 2.76 mmol). 1-Boc-piperazine (771 mg, 4.14 mmol, Aldrich) was added, followed by triethylamine (0.77 mL, 5.52 mmol). The mixture was stirred at 60° C. overnight. It was then heated at 120° C. for 10 min and at 180° C. for 15 min using the microwave synthesizer. Upon cooling, the reaction mixture was concentrated, and the residue was diluted with ethyl acetate. The organic layer was washed with water, brine, and concentrated. Purification of the crude residue by flash column chromatography gave 4-[3-(benzhydryl-sulfamoyl)-propyl]-piperazine-1-carboxylic acid tert-butyl ester as yellow oil (688 mg).
