The known 5-amino-4-cyano-1-phenylpyrazole (I) was coupled with 4-chlorobenzenesulfonyl isocyanate (II) to produce the sulfonyl urea (III). This compound was converted to the corresponding sodium salt by evaporation of its solution in aqueous NaOH.
The intermediate amino pyrazole (I) was prepared as follows. Acylation of malononitrile (IV) with acetyl chloride (V) in the presence of Et3N afforded (1-hydroxyethyliden)malononitrile (VI). Subsequent methylation of the hydroxyl group with dimethyl sulfate gave enol ether (VII). Alternatively, malononitrile (IV) was converted to the ethyl enol ether (VIII) by condensation with triethyl orthoacetate in the presence of Ac2O. Cyclization of either (VII) or (VIII) with phenylhydrazine (IX) furnished 5-amino-4-cyano-1-phenylpyrazole (I).