Journal of the Chemical Society. Perkin transactions I p. 553 - 555 (1982)
Update date:2022-08-03
Topics:
Butler, Richard N.
James, John P.
Oxidation of bis-(4-nitrophenylhydrazone)s of 1,3-diketones containing an α-CH between the hydrazone chains resulted in cyclization with fragmentation, giving pyrazoles.The reaction is considered to involve dehydrogenation of the conjugated tautomeric enamine form of the bis-hydrazone, giving a cis-azo-hydrazono-alkene intermediate.When the postulated azo-hydrazono-alkene intermediate had trans-stereochemistry, unfavourable for cyclization, as in the oxidation of cycylohexa-1,3-dione bis-(4-nitrophenylhydrazone), the azo-alkene was stable and was the main product.When the conjugated enamine tautomeric form of the 1,3-bis-hydrazone cold not exist, as with 3,3-dimethylpentane-2,4-dione bis-(4-nitrophenylhydrazone), pyrazoles were not formed and the hydrazone chains behaved as isolated monohydrazones.
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