Reaction of 4‐hydroxy‐5‐oximino‐3‐thiophenecarboxylates with hydrazines. Formation of pyrazolylthiohydroxamic acids

The reactions of 4‐hydroxy‐5‐oximino‐3‐thiophenecarboxylates with hydrazine and substituted hydrazines have been investigated. The products of the reactions have been shown to be pyrazole‐3‐ or 5‐thiohydroxamic acids rather than the hydrazones previously described by Benary and Silberstrom. Two alternate mechanisms are proposed which account for the regiochemical outcome. The structures of the pyrazole‐3‐ and 5‐thiohydroxamic acids and corresponding nitriles have been proven by independent synthesis, comparison to known compounds, and by proton and carbon magnetic resonance and long range HETCOR experiments.