The reaction of 4-nitrophenol (I) with 2-chloroethyl isocyanate (II) in pyridine leads to the activated carbamate (III), which is nitrosated by reacting with nitrosyl chloride in pyridine at -20 C to yield 4-nitrophenyl N-(2-chloroethyl)-N-nitrosocarbamate (IV). The nitrosated molecule (IV) is reacted with 2-(methylthio)ethylamine (V) in THF at ordinary temperature affording the sulfure urea (VI), which is then oxidized to the sulfonyl compound (VII) by hydrogen peroxide in formic acid at 50 C.