A-Diketone monohydrazones

Ketones are obtained from a-diketones by reduction with hydrogen sulfide in a pyridine-methanol solution [237], by refluxing with 47% hydriodic acid in acetic acid (yield 80%) [916], and by decomposition of monohydrazones with alkali [923]. Reduction of a-diketones to hydrocarbons is achieved by decomposition of bis-hydrazones by alkali [923]. 

Saturated 1,4-dicarbonyl compounds give 1,4-dihydro-pyridazines or -pyridazinones, etc., which are easily oxidized. 1,2-Diketone monohydrazones and esters containing a reactive CH2 group give 3-pyridazinones (95 — 96) (54HCA1467). 

The earliest methods for preparing cyclic a-diazo ketones involved the oxidation of the monohydrazones prepared from a-diketones, generally using mercuric oxide.7,8 Recent modifications of this procedure include the use of calcium hypochlorite in aqueous sodium hydroxide or activated manganese dioxide as oxidants.1 The latter reagent, especially, hoc ms preferable to mercuric oxide. The base-catalyzed decomposition of tile monotosylhydrazoneH of a-diketones has been... 

The monohydrazones of a-diketones react with acetone and nickel(II) acetate to give azine complexes (82), which can be converted to macrocyclic complexes by reaction with 1,2-diamino-ethane, but not 1,3-diaminopropane (Scheme 34).179-181... 

As already indicated, 1,3,5-triketones react anomalously with hydrazines. Interaction of the sodium enolate of a diketone and an a-halogenohydrazone, however, leads to the monohydrazone of a... 

Saturated 1,4-dicarbonyl compounds give 1,4-dihydro-pyridazines or -pyridazinones, etc., which are easily oxidized. 1,2-Diketone monohydrazones 124 and esters 125 containing a reactive CH2 group give 3-pyridazinones 126 (Scheme 64) . A popular modification of this approach is the Ugi four-component condensation of diarylethane-l,2-dione monohydrazones 127 with isocyanides, aldehydes, and methylene active acids leading to the corresponding substituted pyridazin-3(2//)-ones 128 (Scheme 65) The intermediate Ugi condensation products have never been observed because of their tendency to cyclize <2003S691>. 

Monohydrazones of a-diketones are converted into a-diazoketones [389, 391, 406], which, at higher temperature, give ketenes [5S5, 406] (equation 462). 

Dihydrazones of a-diketones, when treated with mercuric oxide at higher temperatures, yield acetylenes [393, 394, 395, 396], Diphenylacet-ylene is obtained by refluxing benzil dihydrazone with mercuric oxide [396] in benzene or by refluxing benzil monohydrazone with mercurous trifluo-roacetate in ether for 2 h (yield 43%) [405], The oxidation of dihydrazones... 

Among syntheses in which a diazoalkane is added to an o ,)3-unsaturated ketone and the adducts are converted to cyclopropyl ketones, an unusual example is provided by the a-diketone, l,2,5,6-tetramethyltricyclo[3.1.0.0 ]hexane-3,4-dione (26), which was converted to the diazo compound 27 (via the monohydrazone) and the enone 28 (via a Wittig reaction). Mixing of these two products gave the /rani-configurated 4,5-dihydro-3//-pyrazole 29 (85%), which was photochemically converted to the symmetrical trani-configurated cyclopropane 30 (55%)." ... 

Allylation of acylsilanes and a-ketoesters proceeds normally. Monoallylation of a-diketones is also easily realized, whereas glyoxal A7Ai-monohydrazone gives 1,7-octa-diene-4,5-diol. However, sequential reactions of the glyoxal monohydrazone with RLi and then allylindium reagent lead to unsymmetrical diols. ... 

Sodium metaperiodate can be used for the oxidation of dihydrazones of a-diketones 910 to acetylenes 911 in high yields under mild condition (Scheme 3.372) [1360]. This procedure is also suitable for the deprotection of monohydrazones of aldehydes and ketones. This mild and efficient procedure is applicable to substrates with either electron-withdrawing or electron-donating substituents [1360]. 

An easy and general pyridazine synthesis from a-dione monohydrazones and either jS-keto-esters or jS-diketones has been reported. ... 

Introduction of the future C-5 into a 1,2-diketone monohydrazone, at the correct oxidation level and via a Wittig reaction, leads to pyrazoles. ... 

A convenient route to pyridazine derivatives is found in the reaction of monohydrazones of 1,2-diketones with DMAD. The reaction of benzil monohydrazone with DMAD, for example, gives a mixture of products consisting of dimethyl 5,6-diphenylpyridazine-3,4-dicarboxylate (135), benzil dimethyl oxaloacetate ketazine (136) and benzil bisketazine (137). A similar reaction of acenaphthenequinone... 

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