The cyclization of phenylhydrazine (I) with 3-[4-(methylsulfanyl)phenyl]acrylonitrile (II) by means of NaOEt in refluxing ethanol gives the aminopyrazoline (III), which is dehydrogenated by means of MnO2 in dichloromethane to yield the 3-aminopyrazole (IV). The diazotation of (IV) with NaNO2 and HCl in water, followed by a treatment with Cu2Cl2, affords the 3-chloropyrazole (V), which is finally oxidized to the target sulfone by means of MCPBA in dichloromethane.