Hydrazones dimethyl

Oxidative Couplings of Heterocyclic Hydrazones. This method has opened the way to the preparation of azo derivatives of diazo compounds unobtainable by other means, ie, heterocycHc compounds ia which the diazotizable amino group is conjugated with the heterocycHc nitrogen atom as ia 2- and 4-amiQopyridine, compounds which do not normally yield stable diazonium salts (38). The reaction occurs as illustrated by equation 7 for the iateraction of (A/-methylcarbostyryl)hydrazone [28219-37-6] and dimethyl aniline the overall process is oxidation. 

Basic Red 22 (134), which contains 1 part ia 7 of the yellowish red 1,4-dimethyl isomer, Basic Red 29 (135), and Basic Yellow 25 (136) are all examples of delocalized cationic azo dyes. Dyes of this type can also be synthesized by Hbnig s oxidative coupling reaction of heteroaromatic hydrazones with tertiary aromatic amines. 

Katritzky and co-workers studied the mechanism of this reaction in detail. His work involved a NMR study of 16 reactions of methyl-, phenyl-, 1,2-dimethyl-, and l-methyl-2-phenylhydrazine with /3-keto esters. In many cases starting materials, intermediates, and products were detected simultaneously. Most reactions proceed by nucleophilic addition of the less hindered hydrazine nitrogen atom to the keto carbon of the keto ester. For example, the pathway given in Scheme 3 for the reaction of methyl 3-oxobutanoate 9 with methyl- or phenyUiydrazine 2 (R = Me or Ph) was found to be dominant. The initially formed addition product 10 dehydrates to hydrazone 11, which then isomerizes to hydrazone 12. Intermediate 12 then cyclizes to pyrazol-3-one 13, which tautomerizes to the kinetically more stable pyrazol-3-otie 14 [87JCS(P2)969]. 

To prepare fervenulin 4-oxides 12 or toxoflavine 4-oxides 146, it is convenient to use the reaction of l,3-dimethyl-2,4-dioxopyrimidin-6-yl hydrazone 147 or N-(3-methyl-2,4-dioxopyiimidin-6-yl) iV-methylhydrazone 148 with potassium nitrate in acetic acid [75CPB1885,76CPB338,76JCS(CC)658,82JHC1309,93CPB362]. Diethyl azodicarboxylate can be used instead of potassium nitrate [76JCS(P1 )713]. 

The classical procedure for the Wolff-Kishner reduction—i.e. the decomposition of the hydrazone in an autoclave at 200 °C—has been replaced almost completely by the modified procedure after Huang-Minlon The isolation of the intermediate is not necessary with this variant instead the aldehyde or ketone is heated with excess hydrazine hydrate in diethyleneglycol as solvent and in the presence of alkali hydroxide for several hours under reflux. A further improvement of the reaction conditions is the use of potassium tcrt-butoxide as base and dimethyl sulfoxide (DMSO) as solvent the reaction can then proceed already at room temperature. ... 

Chemical Name 1 (2H)-Phthalazinone-(1,3-dimethyl-2-butenylidene)-hydrazone Common Name Mesityl oxide (1-phthalazinyl) hydrezone... 

Acetals of A. A -dimethyl hydrazones 4, derived from glyoxal (1) and various enantiomerically pure diols (c.g., 3a-f)24, are readily prepared by transacetalization of 2. Addition of methyl-or butyllithium to 4 provides the corresponding hydrazines in good yield (70-88%) and moderate to excellent diastereoselectivity (see Table 3)4,5. 

In order to prove the utility of this method and to ascertain the absolute configuration of the products, (S)-alanine has been enantioselectively prepared. The key step is the addition of methyllithium to the AjA -dimethyl hydrazone acetal 4c, derived from diol 3c. In accordance with 13C-NMR investigations it can therefore be assumed that all major diastereomers resulting from the addition of organolithium reagents to hydrazone acetals 4a-c derived from diols 3a, 3b or 3c (Table 3, entries 1 -6) have an S configuration at the newly formed stereogenic center. 

The aminalizalion of A.A -dimethyl hydrazone 5a derived from glyoxal 1 with enantiomerically pure 1,2-diamines 7a and 7b25 26 containing a C2 axis of symmetry is a straightforward process (in contrast to the acctalization with diols). 

Table 4. Addition of Organometallics to Chiral /V,jV-Dimethyl Hydrazone Aminals Sb6,7 HsCe,...

The reaction of 3-amino-2-hydrazino-4(3// )-pyrimidinones 234 with dimethyl acetylenedicarboxylate gave pyrimidinylidene hydrazones 236... 

Considerable difficulties are often experienced in the preparation of basic dyes from quaternised heterocyclic diazo components. An alternative technique is to use an oxidative coupling procedure, in which a mixture of a hydrazone and a coupling component is treated with a mild oxidising agent, such as a hexacyanoferrate(III) [102] an azo compound is then produced as shown in Scheme 4.36 for the synthesis of Cl Basic Red 30 (4.100) [103]. Quaternisation of heterocyclic derivatives can lead to the formation of mixtures of isomers, as in the case of Cl Basic Red 22 (4.101). As well as the 2,4-dimethyl derivative shown, the product contains about 15% of the 1,4-dimethyl isomer [104]. 

Electron-deficient allenes also undergo hetero-Diels-Alder reactions. N,N-Dimethyl-hydrazones 193 reacted with allenedicarboxylate 110a in refluxing acetonitrile to give 2-carboxy-3-pyridineacetic acid diesters [157]. 

Derivatization of carbonyl groups (reduction or formation of N,N-dimethyl-hydrazones or oximes)... 

Reduction of the carhonyl group to methylene is carried out hy Clemmensen reduction [160, 758], hy Wolff-Kizhner reduction [280, 282], or hy its modifications decomposition of hydrazones with potassium /er/-butoxide in dimethyl sulfoxide at room temperature in yields of 60-90% [845], or hy reduction ofp-toluenesulfonylhydrazones with sodium borohydride (yields 65-80%) [811] (p. 134). 

Products containing two adjacent stereogenic centers were obtained as mixtures of diastereoisomers that could be separated by column chromatography (dr values. Scheme 6.12). The N,N -dimethyl acetaldehyde hydrazone appeared remarkably... 

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