(4-Chloro-2-nitro-phenyl)-(3-methanesulfonyl-propyl)-carbamic acid tert-butyl ester was prepared according to Scheme 1. To a solution of tert-butyl 4-chloro-2-nitrophenylcarbamate (580 mg, 2.1 mmol) in DMF (5 mL) was added NaH (170 mg, 4.3 mmol, 60 wt %). The mixture was stirred for 30 min at RT, then 3-(methylsulfonyl)propyl 4-methylbenzenesulfonate (0.75 g, 2.56 mmol) was added. The solution was heated to 50° C. and stirred for overnight. After cooled to RT, H2O (30 mL) was added and the solution was extracted with DCM (40 mL×3). The organic layer was dried over anhydrous and concentrated. The residue was purified by prep-TLC (DCM) to give tert-butyl 4-chloro-2-nitrophenyl(3-(methylsulfonyl)propyl)carbamate (360 mg, yield: 69%) as pale oil. MS obsd. (ESI+) [(M+H)+]: 393.0.
