Synthesis of pyrido-1,2,4-thiadiazines related to antihypertensive 1,2,4-benzothiadiazine-1,1-dioxides

Oxidation of 3-phenyl-2H-pyrido[2,3-e]-1,2,4-thiadiazine with sodium hypochlorite and, separately, m-chloroperoxybenzoic acid afforded a 1,1- dioxide and a 5-oxide derivative, respectively. Further examples of such 1,1- dioxide derivatives were synthesised by treating 2-amino-5-methylpyridine with orthoesters and these were subsequently oxidised to novel 1,1,5- trioxides. A short route has been developed for the synthesis of 4- aminopyridine-3-sulfonamide which was used for the preparation of 4H- pyrido[4,3-e]-1,2,4-thiadiazine 1,1-dioxides; oxidation of the parent member of the series gave a 1,1,7-trioxide derivative. 3-Aminopyridine-4-sulfonamide has been prepared, and then condensed with triethyl orthoformate to afford 4H-pyrido[3,4-e]-1,2,4-thiadiazine 1,1-dioxide.