Oxidation of arylacetylhydrazones of carbonyl compounds with lead tetraacetate

Abstract

Oxidation of the title compounds 8, 9 with lead tetraacetate at room temperature gives a variety of products depending on the substituents on the carbonyl carbon atom. Thus, on oxidation of the aldehyde derivatives 8 1,3,4‐oxadiazolo derivatives 10 are obtained in good yields. However in some cases formation of N‐acetyl‐N‐arylacetyl‐N′‐benzoylhydrazines 11 is also observed, whereas oxidation of the ketone hydrazones 9 gives in good yields the 2H,5H‐1,3,4‐oxadiazoles 15 or substituted monoacetoxy‐ 17 and diacetoxyalkanes 18. The reaction mechanisms are also discussed.

Transformation of phenolic hydroxyl into acyl group: a new tool in organic synthesis

“…10 Thus, we thought that the hydroxyl group could interact with the hydrazone moiety to lead to the formation of 1,2-benzisoxazole N-imines 11. However, we found that monoacylhydrazones of type 10 do not yield N-imines 11 or the corresponding 1,3,4-oxadiazolines that would be formed if the reaction proceeded according to the literature data [4][5][6][7] about the unsubstituted hydrazones (Scheme 1), but instead they undergo a rearrangement resulting in "replacement" of the phenolic hydroxyl with an acyl substituent to give 3 1,2-diacylbenzenes 12, in excellent yields 70-90%, Scheme 3. o-Diacylbenzenes have been of interest primarily as fluorescence reagents for both qualitative and quantitative high sensitivity analyses for amines and amino acids.…”

“…It has been known [4][5][6][7] o-Hydroxyarylketones are very interesting molecules both because of their potential to serve as starting materials in organic synthesis as well as because of their applications. 9 The presence of a hydroxyl and a carbonyl group at ortho positions to each other at the benzene ring allows the formation of novel heterocycles as well as other non-heterocyclic aromatic compounds.…”

“…Intermediate 17 is indeed the final product obtained [4][5][6][7] by LTA reactions with o-unsubstituted N-acylhydrazones as hydrazones 1 in Scheme 1. The presence of the hydroxy group seems to be crucial to the mechanism of the reaction.…”