Oxidation of hydrazones

Analogous to the oxidation of hydrazones to azo compounds, A-unsubstituted pyrazolidines are oxidized to A -pyrazolines. For example, the blcyclic pyrazolidine (415) when treated with silver oxide yields the pyrazoline (416) (65JA3023). Pyrazolidine (417) is transformed into the perchlorate of the pyrazolium salt (411) by reaction with mercury(II) acetate in ethanol followed by addition of sodium perchlorate (69JOU1480). 

The higher diazoalkanes can be made by Pb(02CCH3)2 oxidation of hydrazones.129... 

Several approaches to the 1,2,3-triazole core have been published in 2000. Iodobenzene diacetate-mediated oxidation of hydrazones 152 led to fused 1,2,3-triazoloheterocycles 153 <00SC417>. Treatment of oxazolone 154 with iso-pentyl nitrite in the presence of acetic acid gave 1,2,3-triazole 155, a precursor to 3-(W-l,2,3-triazolyl)-substituted a,P-unsaturated a amino acid derivatives <00SC2863>. Aroyl-substituted ketene aminals 156 reacted with aryl azides to provide polysubstituted 1,23-triazoles 157 <00HC387>. 2-Aryl-2T/,4/f-imidazo[43-d][l,2,3]triazoles 159 were prepared from the reaction of triethyl AM-ethyl-2-methyl-4-nitro-l//-imidazol-5-yl phosphoramidate (158) with aryl isocyanates <00TL9889>. 

Free or benzo-fused 1,2,3-triazoles 286 have been prepared by iodobenzene diacetate-mediated oxidation of hydrazones 285 (Equation 37) <2000SC417>. 

Mercuric oxide, use in oxidation of hydrazones, 50, 28 with 3-chlorocyclobutanecar-boxylic acid and bromine to give l-bromo-3-chlorocyclo-butane, 51, 106 MERCURIC OXIDE-MODIFIED HUNS-DIECKER REACTION 1-BRQMO-... 

In 1981 we published the first paper [22] on the synthesis of s-triazolo[4,3-a]pyridinium salts, 4, by the anodic oxidation of hydrazones 3 in the presence of pyridine (Scheme 5). In our working mechanistic scheme we proposed nitrilimine as the possible intermediate and pointed out that this reaction opens the door to a wide range of heterocyclic systems via anodic oxidation of aldehyde hydrazones through 1,3-dipolar cycloaddition reactions of the nitrilimine involved. 

This paper prompted Jugelt, Grubert and co-workers to use the same reaction concept and accomplish several very good synthetic reactions [23-28]. When they performed t he oxidation of hydrazones in the presence of imidazole... 

We believe that the intermediate generated by anodic oxidation of 3 is the cation 3a and not nitrilimine 3b. The generation of the cation intermediate was postulated in several papers on the anodic oxidation of hydrazone derivatives [38-41], W also believe that both heteroaromatic and Schiff bases react with the cation 3a as nucleophiles rather than dipolarophiles. The most likely mechanism of the oxidation of the hydrazone 3 in the presence of heteroaromatic and Schiff bases, which would best fit the observed electrochemical and preparative results, can be described in the form of Scheme 8. 

Formation of the Nitrogen-Nitrogen Bond 3.4.1 Oxidation of Hydrazones and Formazans... 

Diazo esters can also be prepared from glycine esters by treatment with nitrous acid [966] or with alkyl nitrites. Further methods include the oxidation of hydrazones, oximes (Forster reaction), and semicarbazones, the base-induced... 

Of the general methods for the generation of transient nitrile imines for use in synthesis (19), perhaps the most convenient are the base-induced dehydrochlorination of hydrazonyl chlorides and the oxidation of hydrazones. Developments in both of these areas have either increased the convenience of the method or given a deeper insight into the reaction mechanism. 

The oxidation of hydrazones 143 provides, in principle, a very convenient route to nitrile imines from easily accessible starting materials. However, the earliest reagent used, lead tetraacetate, was of limited effectiveness as yields were low and the reaction often gave high yields of diacyUiydrazides as byproducts. Work has been done on the apphcation of several other oxidants to this process to produce a more effective general route. The one that has proved most popular is chloramine T (A(-chloro-A(-sodio-p-toluenesulfonamide, CAT) which is used under mild conditions and has been shown to work well for both cycloaddition (79) (e.g., in the preparation of 146 from 145) and electrocychzation (80) reactions. 

Figure 11. Proposed mechanism of nitrosamine formation by cleavage of a four-membered ring in the oxidation of hydrazone X(2A)...

By conventional procedures, 106 gm of benzaldehyde reacts in 600 ml of ether with 66 gm of anhydrous hydrazine to give benzalhydrazone which is directly oxidized in anhydrous ether with 300 gm of mercuric oxide to phenyl-diazomethane.) (See Volume I, Chapter 15, p. 398, for oxidation of hydrazones, p. 390 for an alternative preparation of phenyldiazomethane.)... 

Many examples of ring closures by oxidation of hydrazone derivatives have been reported. Anodic oxidation of chalcone72 phenylhydrazone (17) performed in CH3CN—LiCI04 at platinum, using controlled potential electrolysis, gave 1,3,5-triphenylpyrazole (15-40% yield) (18), 1,3,5-triphenyl-A2-pyrazoline (19), l,3,5-triphenyl-A2-pyrazolinium perchlorate, 4,4-bis[3,5-diphenyl-A2-pyrazolinyl-(l)]-biphenyl (20), the diperchlorate of 20, and 4,4 -bis-[3,5-diphenylpyrazolyl-(l)]-biphenyl (21) [Eq. (30)]. 

Firmenich 315) used the oxidation of hydrazones for a novel syntheses of musk fragrances ... 

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