Cleavage phenylhydrazones

The coupling of enamines with aromatic diazonium salts has been used for the syntheses of monoarylhydrazones of a-diketones (370,488-492) and a-ketoaldehydes (488,493). Cleavage of the initial enamine double bond and formation of the phenylhydrazone of acetone and acetophenone has been reported with the enamines of isobutyraldehyde and 2-phenylpropionalde-hyde. Rearrangement of the initial coupling product to the hydrazone tautomer is not possible in these examples. 

The methyl group position was fixed both by cleavage of the isoxazole ring with sodium ethylate and by isolation of the cyanacetone sodium salt 125. The reaction of this salt with phenylhydrazine resulted in the phenylhydrazone of cyanacetone (126) (69ZOR1179). 

Reductive cleavage of phenylhydrazones of carbonyl compounds provides a route to amines. The reduction is carried out conveniently in ethanol containing ammonia over palladium-on-carbon. Ammonia is used to minimize formation of secondary amines, derived by addition of the initially formed amine to the starting material (160). Alternatively, a two-phase system of benzene, cyclohexane, toluene, or dioxane and aqueous hydrochloric acid can be used. 

Phenyl formate, physical properties, 6 292t Phenyl glycidyl ether (PGE), 10 376 AT-Phenylglycine, 1 138 9 279 AT-Phenylglycinonitrile, 3 174 Phenylhydrazine synthesis, 13 573 Phenylhydrazone cleavage, microwaves in, 16 562... 

Large-scale reduction of phenylhydrazones at mercury or lead in ethanolic hydrochloric acid or 30-50% sulphuric acid results in cleavage of the nitrogetr-... 

Under the action of phenylhydrazine or 5-amino-3-phenylpyrazole on pyran 59b only benzaldehyde phenylhydrazone 271 is formed, probably, as the result of pyran retro-cleavage (82M53). A similar reaction with malononitrile, leading to pyran 59a, a product of formal displacement of a cyanoacetic moiety, possibly results from a similar cleavage (82M53) (Scheme 108). 

Phenylhydrazine also causes ring cleavage of chromones, but under some conditions the phenylhydrazone is formed (Scheme 23) (73MI22302, 77MI22303). 

Benzaldehyde phenylhydrazone with DM AD gave 8% of dimethyl 1,3-diphenylpyrazole-4,5-dicarboxylate (136) together with 35% of trimethyl pyrazoletricarboxylate (138), which the authors suggest is obtained from the primary adduct 137 by Michael addition of a second mole of DMAD followed by cleavage, as shown.129... 

In saccharides, cleavage by periodic acid or sodium periodate occurs between any carbons possessing/ree hydroxy lie groups. Thus glucosazone treated with periodic acid in aqueous ethanol at room temperature is degraded to the l,2-bis(phenylhydrazone) of mesoxalaldehyde (propanone-dial) in 85% yield [759]. 

In acid solution cinnolines are reduced to dihydrocinnolines a 1,4-dihydrocinnoline may be regarded as derived from a phenylhydrazone, which is reduced with cleavage of the nitrogen-nitrogen bond [101, 147] ... 

A reduction route similar to that of phenylhydrazones [229] seems to be rather general for azomethine derivatives of hydrazine [229] as it s followed by cyclic and acylic phenylhydrazones, semicarbazones, azines, cyclic hydrazones, and acylated cyclic and acyclic hydrazones [231] under pro tic conditions in DMF, acylated hydrazones of aromatic aldehydes are reduced with saturation of the C=N bond and cleavage of the N-N bond at a more negative potential [232]. The suggestion that the cleavage of the N-N bond precedes the saturation of the azomethine bond is also an essential part of the interpretation of many of the ring contractions of heterocyclic compounds (Chapter 18). 

A reaction that involves both a carbon-carbon and a nitrogen-nitrogen cleavage is found in the reduction of 2-phenyl-4-carboxytriazole by Na(Hg) in slightly alkaline solution [118]. The reaction probably starts with a reductive cleavage of the ring, followed by loss of CN and further reduction of the phenylhydrazone thus obtained to the hydrazine ... 

Kereselidze, J., Raevski, K. The quantum-chemical study of N-N bond cleavage in phenylhydrazones. Izv. Akad. Nauk Gruz. SSR, Sen Khim. 1996, 22, 170-172. 

Although the 2,4-dinitrohydrazone free acid is relatively stable in water, the 2-methoxy 4-nitrophenylhydrazone decomposes at acid or near neutral pH, as does the unsubstituted phenylhydrazone, to a mixture of phosphate and cyanophosphate. This can be rationalized as a fragmentation involving cleavage of both a P-C bond of the bisphosphonate and the N-N bond of the hydrazone, with an aniline as the leaving group. The basicity of the nascent amino nitrogen... 

Cleavage of—N—derivatives. This reagent is more effective than pyruvic acid for the cleavage of phenylhydrazones and semicarbazones. Reaction with a phenyl-hydrazone produces 3,5-dimethyl-N-phenylpyrazoIe and liberates the free carbonyl compound. 

Four diastereoisomeric forms of the phenylhydrazone (37) have been obtained by ring cleavage of a A -l,2,3-diazaphospholine-chIorine adduct with methanol, as shown in Scheme 6. 

A. R. Hajipour, H. Adibi, and A. E. Ruoho, Wet silica-supported permanganate for cleavage of semicarbazones and phenylhydrazones under solvent free conditions, J. Org. Chem., 68 (2003) 4553-4555. 

Nonaqueous procedures for oxidation of mandelic esters and the cleavage of p-nitro-phenylhydrazones and semicarbazones involves treatment with ammonium chlorochromate adsorbed on alumina. ... 

The 2-oxocyclopentane-l-carboxylic ester 36 is coupled with benzenediazonium chloride in a basic medium with simultaneous acid cleavage of the product 37. The resulting phenylhydrazone of the a-... 

Hydrolytic cleavage of C—N bom. mverts phenylhydrazones, p-nitropi - fluxing dichloromethane to the paier... 

Serotonin has been synthesised by several routes the method shown relies on a Fischer indole synthesis, the requisite phenylhydrazone being constructed by a process known as the Japp-Klingemann reaction in which the enol of a 1,3-dicarbonyl compound is reacted with an aryldiazonium salt, with subsequent cleavage of the 1,3-dicarbonyl unit. 

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