Fungitoxicity of 6H‐pyrazolo[3,4‐c][l,2,5]thiadiazine‐2,2‐dioxides

A base‐promoted cyclisation of 4‐nitroso‐5‐benzylsulphonamidopyrazoles (VII) afforded 6 H ‐pyrazolo [ 3,4‐ c][ 1,2,5 ] thiadiazine‐2,2‐dioxides (VIII). They were tested in vitro for antifungal activity against a series of phytopathogenic fungi of different taxonomic classes. Five of the compounds had noteworthy activity; in particular 6 H ‐3‐phenyl‐5‐methyl‐7– ( 3,4‐dichlorophenyl) pyrazolo [ 3,4‐ c][ 1,2,5 ] thiadiazine‐2,2‐dioxide (VIIIc) at the concentration of 200 mg litre −1 completely inhibited the growth of Pythium ultimum, Corticium solani and Sclerotinia minor.