N-Sulfonylamidines. Part IV. Intramolecular cyclization of N-sulfonylamidines of 2-oxoacids: A new synthesis of 3-aminoisothiazole S,S-dioxides

N-alkylsulfonylamidines of α-ketoacids 3 bearing both a carbonyl group and at least one H-atom near to the SO2 group give easily an intramolecular ring-closure reaction by action of potassium t-butoxide producing the 3-amino-4,5-dihydro-4-hydroxy-isothiazole S,S-dioxides 4. Compounds 4 are transformed by thionyl chloride into the corresponding chloro-derivatives 5 which in turn are dehydrochlorinated by potassium carbonate to substituted 3-amino-isothiazole S,S-dioxides 6.