Some 1H-4,1,2-benzothiadiazines and 1H-4,1,2-benzothiadiazine 4,4-dioxides

Interamolecular displacement of the o-nitro-group of 1-(2-nitrophenylthio)pyruvaldehyde 1-phenylhydrazone, under basic conditions, gives 3-acetyl-1-phenyl-1H-4,1,2-benzothiadiazine which was oxidised to the 4,4-dioxide. Ethyl 2-nitrophenylsulphonylglyoxylate phenylhydrazone gives only 2-nitrodiphenylamine under these conditions, but reduction to the 2-amino-compound and diazotisation yield 3-ethoxycarbonyl-1H-4,1,2-benzothiadiazine 4,4-dioxide. Hydrolysis and decarboxylation give the parent 1H-4,1,2-benzothiadiazine 4,4-dioxide.