Tetronic acids and derivatives. Part V. Synthesis of 5-hydroxy-1H-pyrazoles via 4-hydrazino-5H-furan-2-ones. Reaction of hydrazines on tetronic acids

The conversion of tetronic acids 1 to 3(1-hydroxy alkyl)-5-hydroxy-1H-pyrazole derivatives 3, 5, 7 and 12 is described. The formation is shown to proceed via base-catalyzed rearrangement of the intermediate 4-hydrazino-5H-furan-2-one derivatives.