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

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.