Synthesis of 4-oxo-1,4-dihydro-6h-furo[3,4-c]pyrazole and 4-oxo-1,4,5,6-tetrahydropyrrolo[3,4-C]pyrazole Systems from Acyl Tetronic and Tetramic Acids

Abstract

The reaction of acetyl tetronic acid la with phenylhydrazine had been reported to lead to 3-(1-phenylhydrazonoethyl)-tetronic acid 3, which by ring closure afforded the pyrazole-lactone 5a¹. On the other hand, condensation of acetyl tetramic acids 2a,b with phenylhydrazine and methylhydrazine had been described as yielding 4-oxo-2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazole derivatives 9 via the hydrazones 4 ². The lack of reactivity of the carbonyl of the acetyl side chain towards hydrazines is amazing in view of the affinity shown by this group for reactions with amines ^3–5. We therefore reinvestigated these structures and we now wish to present evidence for the formation of 1-substituted-4-oxo-1,4-dihydro-6H-furo[3,4-c]pyrazoles 5 and 6 and 1-substituted-4-oxo-1,4,5,6-tetrahydropyrrolo[3,4-c]pyrazoles 7 and 8 and not 2,4,5,6-tetrahydropyrazoles 9 as previously described 2.