Carbonyl compounds regeneration from hydrazones

Carbonyl compounds are regenerated from hydrazones by Pd-catalyzed reaction with tin(ll) chloride. ... 

Regeneration of carbonyl compounds from the hydrazones (75-98%) [53] and from semicarbazones (55-90 %) [54] has also been achieved with bismuth trichloride. 

Regeneration of carbonyl compounds from certain derivatives. Ketones can be recovered in satisfactory yield from the phenylhydrazones, p-nitrophenyl-hydrazones, tosylhydrazoncs, oximes, and semicarhazones by reaction with 1 equivalent of (C6H,Se0)20. 2,4-Dinilrophenylhydrazones and N,N-dimethyl-hydrazones arc inert under even rather vigorous conditions. The reagent can also be used to regenerate aldehydes from oximes or tosylhydrazones. 

Oxidative cleavage of hydrazones. Carbonyl compounds can be regenerated from 2,4-dinitrophenylhydrazones, tosylhydrazones, or N-methyl-N-tosylhydra-zones in 80-95% yield by oxidation with sodium nitrite in TFA or HOAc (0-5°, 1-2 hours). In the case of tosylhydrazones, the other product of cleavage has been identified as tosyl azide, the product of reaction of tosylhydrazine with nitrous acid. 

Table 1 Reagents for Regeneration of Carbonyl Compounds from Ketone and Aldehyde Hydrazones...

A new method for cleavage was recently reported by Enders. Treatment of the hydrazone with three equivalents of sodium perborate regenerate the carbonyl compound in 70-95% yield according to equation (36). This oxidative cleavage was chemoselective and left carbon-carbon double bonds intact. This chemoselectivity plus the neutral hydrolytic conditions and the low cost of the oxidant make this method quite attractive, liie main disadvantage of this method is the relatively long reaction time required, ranging from 4-24 h for aliphatic ketone hydrazones to 2-3 d for aromatic ketone hydrazones. 

Many other reagents have been used to cleave hydrazones and to regenerate carbonyl groups. Table 1 lists some of these other examples of procedures to regenerate carbonyl compounds from their N,N-d -alkylhydrazones. 

Regeneration of Carbonyl Compounds from Oximes, Hydrazones, Semicarbazones, Acetals, 1,1-Diacetates, 1,3-Dithiolanes, 1,3-Dithianes, and 1,3-Oxathiolanes ... 

It is usually unnecessary to isolate such hydrazones during the working up the mixture is partitioned between water and a water-insoluble solvent such as ether. The hydrazones then remain in the aqueous phase, and the other organic substances are removed in the organic phase. The carbonyl components are finally regenerated from the aqueous hydrazone phase by acid hydrolysis. Considerable fractionation of mixed carbonyl compounds can be achieved by varying the reaction conditions, notably the temperature or pH, of either the condensation or the hydrolysis. Acid-sensitive carbonyl compounds, e.g., citral, may be isolated by exchange from the hydrazone by an excess of formaldehyde.932... 

Chlorination. Amides and carbamates undergo iV-chlorination by NaCl-Oxone. Under the same conditions, oximes afford a-chloro nitroalkanes. - When the chlorine source is absent, regeneration of carbonyl compounds from oximes and hydrazones occurs. ... 

Cleavage of 2,4-dinitrophenylhydrazones. Carbonyl compounds can be regenerated in high yield (80-95%) from the 2,4-DNP derivatives by treatment in DME with a 20% aqueous solution of TiCls at reflux temperature (N2). McMurry and Sylvestri consider that titanous ion reduces the nitro groups to amino groups and then cleaves the hydrazone N—N bond to generate an imine, which is then hydrolyzed readily to the carbonyl compound. 

Regeneration of Carbonyl and Amino Groups. Excellent yields are obtained in the formation of carbonyl compounds from acetals, ketals, tosyl hydrazones (eq 3), oximes, 2,4-dlnltro-phenylhydrazones, and semicarbazones when reactions are carried out in an acetone/water mixture. 

Regeneration of the parent carbonyl compound from tosylhydrazones and 2,4-dinitrophenylhydrazones can be carried out in high yield using sodium nitrite in trifluoroacetic acid. Deprotection of tosylhydrazones using thallium triacetate in acetic add is also elficient. Oximes yield the carbonyl product on treatment with bromine in aqueous sodium bicarbonate, and the same conditions can be used to hydrolyse tosylhydrazones if HMPA is present. Aqueous nitric acid was found to be superior to both sulphuric and hydrochloric adds for the cleavage of the hydrazones (90) to the corresponding cyclohexanones. ... 

The increasing use of oximes and hydrazones as intermediates in the regio-selective modification of carbonyl compounds has led to an upsurge of interest in seeking mild, specific methods for regeneration of the carbonyl function from these derivatives. AjV-Dimethylhydrazones are hydrolysed rapidly under cupric ion... 

Regeneration of carbonyl compounds from their hydrazones and oximes is most commonly carried out by acid hydrolysis and the expulsion of the analyzed carbonyl compound by a more reactive carbonyl compound in the case of oximes and in special circumstances oxidative cleavage can also be applied. 

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