Dimethylamine → 4-fluoro-N,N-dimethylbenzenesulfonamide

A solution of 50 g of 4-fluorobenzenesulfonyl chloride in 250 ml of THF was cooled to 0° C., and then, 100 ml of an aqueous 50% dimethylamine solution was added dropwise thereto, and the mixture was stirred at room temperature for 1 day. To the reaction mixture were added water and ethyl acetate, the mixture was stirred and then the liquids were separated. The organic layer was washed with a saturated aqueous sodium bicarbonate solution and dried, the solvent was evaporated, and disopropyl ether and hexane were added to the residue. Then, the precipitates were collected by filtration and washed with hexane to obtain 49.9 g of 4-fluoro-N,N-dimethyl-benzenesulfonamide. (2) In 600 ml of DMSO were suspended 25 g of (S)-(+3-(tert-butoxycarbonylamino)pyrrolidine, 47.9 g of 4-fluoro-N,N-dimethyl-benzenesulfonamide and 139 g of potassium carbonate, and the mixture was stirred at 130° C. for 1 day. To the reaction mixture were added water and ethyl acetate, the resulting mixture was stirred and the liquids were separated. The organic layer was washed with water, and then dried, and the solvent was evaporated. The residue was dissolved in chloroform, NH silica gel was added thereto and the mixture was allowed to stand for a while, and silica gel was filtered off. The silica gel was further washed with ethyl acetate. The filtrate and the washed solution were combined, and the residue obtained by concentration under reduced pressure was purified by silica gel column chromatography (hexane:ethyl acetate=80:20→67:33) to obtain 8.39 g of tert-butyl [(S)-1-(4-dimethylsulfamoylphenyl)-pyrrolidin-3-yl]carbamate.