Reactions of lead tetra-acetate. Part VII. Some reactions leading to pyrazoles

Abstract

Four 2-pyrazolines have been oxidised to the corresponding pyrazoles in high yield by lead tetra-acetate at room temperature; this reagent has advantages over others which have been used previously. Lead tetra-acetate converts chalcone phenylhydrazone directly into 1,3,5-triphenylpyrazole, in contrast to its reactions with the arylhydrazones of aromatic ketones which give azoacetates. Two 2-pyrazolines which cannot undergo direct aromatisation have been converted into pyrazoles by oxidation with lead tetra-acetate to 4-acetoxy-2-pyrazolines followed by acid-catalysed rearrangement and elimination.