Lead tetraacetate reaction with hydrazones

Enantiomerically pure nitrile imines (211) have also been generated by the lead tetraacetate oxidation of aldehydo sugar p-nitrophenyl hydrazones. Reaction with methyl acrylate gave the pyrazolines as a 1 1 mixture of the (55) and (5R) epimers, which were resolvable in some cases (116). 

The outcome of the reaction of hydrazones with lead tetraacetate is dependent upon the nature of the hydrazone and the reaction conditions. Mechanistically, the reaction was first suggested to imply the formation of a pair of free radicals, Pb(0Ac)3 and the hydrazonyl radical. However, ESR studies failed to detect the presence of radicals in solutions of hydrazones and lead tetraacetate. The reaction was explained by a two step mechanism, involving first the formation of a covalent hydrazone-lead intermediate followed by an intramolecular rearrangement leading to the a-acetoxy products which can then evolve into different derivatives. ... 

Monosubstituted hydrazones of aldehydes (19) are oxidised by lead tetraacetate to afford A/-acetyl AT-acylhydrazones.25-77 The reaction proceeds via a A -hydrazone intermediate which undergoes a ligand coupling reaction to give an hydrazonyl acetate (20) which then rearranges to the final product. Monosubstituted hydrazones of ketones (22) react with lead tetraacetate to give a-azoacetates (23). ... 

Butler70k has discussed reactions of lead tetraacetate with substituted hydrazones as a route to novel heterocyclic ring systems. 

Reaction of hydrazones with lead tetraacetate Acoxy compds. from hydrazones... 

The reaction of aldehyde hydrazones is more complex and requires further study [103]. It is usually carried out with a 90% solution of lead tetraacetate in acetic acid with sufficient additional solvent to bring about homogeneous reaction conditions initially. 

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