Monohydrazones of a-diketones

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... 

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

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]. 

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... 

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... 

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... 

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]. 

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... 

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%)." ... 

Identified by Viani et al. (1965) after steam distillation of a roasted Brazilian coffee, preparative chromatography and characterization by IR spectrum of the product and UV of its monohydrazone. Merritt et al. (1970) found it in headspace of several varieties of roasted but not green beans. The concentration in roasted coffee is estimated at 0.33 ppm by Stofberg and Stoffelsma (1981), at 0.30-0.50 ppm by Silwar et al. (1987) (simultaneous distillation-extraction of the steam-volatile components and preparative GC). Procida et al. (1997) characterized this diketone only in the headspace of a roasted arabica and not in any of the green coffees studied. 

The versatility of Meldrum s acid as a synthon continues to be demonstrated for example, it is alkylated under phase transfer catalysis to give 5,5-dialkyl derivatives209 and it reacts with monohydrazones of 1,2-diketones to give alkylidenes (204) which undergo ring opening-recyclization to pyridazin-3-ones [such as (205)], 210 The catalysis of the hydrolysis of benzylidene-Meldrum s acid has been studied.211 New light has been thrown on the conformation of 2,2,4,4-tetramethyl-1,3-dioxans by a study of their 13C n.m.r. spectra.212... 

The 1,2-diketone undergoes an aldol condensation with the a-CH-acidic ester furnishing the intermediate 12 which is cyclized by N2H4, similar to the formation of 9. In another combination of this three-component system, the monohydrazones of the 1,2-dicarbonyl compounds 13 or hydrazides with a reactive a-CH2 group 14 can be employed for the pyridazin-3(2//)-one synthesis. 

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>. 

In other related syntheses, pyridazines were formed from l,2-diphenyl-3-(diacylmethylene)cyclopropenes, as shown in Eq. (I)46 or from trans-l,2-dibenzoyl-3,3-diphenylcyclopropane 47 Similarly, pyridazines are formed from hydrazines or semicarbazide and y-trichloromethyl-a,jS-unsaturated ketones.48-52 Pyridazines may also be obtained from 1,2-diketones. The reaction between benzoin and hydrazine was investigated in detail. A complex mixture of various compounds is formed, among them 3,4,5,6-tetraphenylpyridazine in low yield.53 Benzil monohydrazones and analogs when treated with vinyltriphenylphosphonium bromide also give 2,3-dihydropyridazines in moderate yield.54,55 Benzil monohydrazone and related compounds react with dimethyl acetylenedicarboxylate to give a mixture of the corresponding ketazine, bisketazine, and pyridazine 2.56 The last is the main product in the absence of solvent. 

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. ... 

The reaction of diketone 75 with hydrazine afforded the monohydrazone 76, which was further oxidized with copper(I) chloride, O2 and p5n idine or activated manganese dioxide to give the a-diazo ketone 77. Thermal decomposition of 77 in methanol gave 2-azuloin methyl ether 79,... 

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