Monosubstituted hydrazones

Monosubstituted hydrazones react with alkenes and alkynic compounds to yield pyrazolidines and pyrazolines, respectively (71LA(743)50, 79JOC218). Oxidation often occurs during the reaction and pyrazoles are isolated as the end product. 

Monosubstituted hydrazones of isatin can exist in at least three tautomeric forms 124-126. According to spectroscopic data, only hydrazone 124 is present in solution (81JOC2764). 

Hydrazones are also useful substrates in the preparation of pyrazoles. Reaction of N-monosubstituted hydrazones with nitroolefins led to a regioselective synthesis of substituted pyrazoles <060L3505>. lf/-3-Ferrocenyl-l-phenylpyrazole-4-carboxaldehyde was achieved by condensation of acetylferrocene with phenylhydrazine followed by intramolecular cyclization of the hydrazone obtained under Vilsmeier-Haack conditions <06SL2581>. A one-pot synthesis of oxime derivatives of l-phenyl-3-arylpyrazole-4-carboxaldehydes has been accomplished by the Vilsmeier-Haack reaction of acetophenone phenylhydrazones <06SC3479>. 

The formation of derivatives of 2,3,6,8-tetraazabicyclo-[3.2.1]3-octene (425) arises from an intramolecular nucleophilic addition to the nitrone group of hydra-zone (424). Compound (424) was prepared by reaction of 2-acyl-3-imidazoline-3-oxides (423) with hydrazine. From the cis- and frans-derivatives (424), exo- and enr/o-isomers (425) were obtained (Scheme 2.197). The reaction of intramolecular cyclization does not occur in cases with monosubstituted hydrazones (316). 

Previously unknown azomethylene derivatives of 1,2,3-dithiazoles 84 were synthesized by the reaction of Appel salt 20 with N-monosubstituted hydrazones 85 (Equation 16) <2004JHC37>. Their formation probably includes the generation of the carbon anion, under the action of a base, which then adds to salt 20. 

From alkylmercaptomethyleneiminium salts various types of amidinium salts have been synthesized. Ammonia, primary and secondary amines, hydrazines and IV-unsubstituted and N-monosubstituted hydrazones were the reaction partners. Side reactions can include the dealkylation of the iminium salt by the amine. If A, A(-unsubstituted salts (141 equation 85) are treated with amines, the desired exchange reaction can be accompanied by nitrile formation. 

N4-monosubstituted hydrazones were the most reactive, independent of the steric or electronic nature of the substituent group. An electro-cyclic reaction mechanism, similar to the one operating in the isothiosemi-carbazone cyclization (81JOC3956), has been proposed for conversion of 41a to 43a (85CPB2678). No intermediate analogous to 45 has been detected (85CPB2678). 

Monosubstituted hydrazones of aldehydes (19) are oxidised by lead tetraacetate to afford A/-acetyl AT-acylhydrazones.25-77 The reaction proceeds via a A -hydrazone intermediate which undergoes a ligand coupling reaction to give an hydrazonyl acetate (20) which then rearranges to the final product. Monosubstituted hydrazones of ketones (22) react with lead tetraacetate to give a-azoacetates (23). ... 

Formation of N,A -dialkylhydrazones from ketones and aldehydes is generally a facile reaction. In the case of most aldehydes, all that is required is stirring of the unsymmetrical A/,fV-dialkylhydrazine with the aldehyde in the presence of a drying agent. In some cases, these reactions can be carried out at room temperature. Ketones react similarly but can require more vigorous conditions. In the case of less-reactive carbonyl substrates, acid catalysts like p-toluenesulfonic acid or azeotropic distillation are commonly used to promote hydrazone formation. Formation of the aldehyde and ketone dimethylhydrazones and of the chiral hydrazone in equations (l)- 4) are examples of typical procedures. Monosubstituted hydrazones such as (6) are prepared in a similar manner (equation 5). These reactions often proceed in near-quantitative yield. 

In general, all osazones having at least one monosubstituted hydrazone residue, such as osazones of t3rpe A and B, respectively, can be converted into osotriazoles. If, however, the osazone has two disubstituted hydrazone residues (t3q>e C), hydrolysis takes place, and the osone hydrazone and, finally, the osone are obtained. 

Condensation Reduction Dihydrazide Monosubstituted hydrazone of aldehyde Alkyl halide(s) 36,45,46 36, 37, 38... 

Donor-acceptor monosubstituted hydrazones (328) have been reported to add in the Michael manner to the iminium species (329), generated from the corresponding enal and the prolinol-type catalyst (R)-(325). The initially formed enamine (330) undergoes a proton transfer followed by hydrolysis to produce adducts (332), which were converted into stable hydrazones (333) by oxidation involving a [1,3] proton shift. ... 

The preparation of a monosubstituted phthalazine hinges on the differing oxidation states of the starting carbonyl groups. Thus reaction of acid-aldehyde (67-4) with hydrazine gives an intermediate (67-5) that contains a hydrazone as well as a... 

The mechanism of these reactions has been studied by several authors. The first product of the reaction between aldehydes and hydrazine or monosubstituted hydrazines is the hydrazone (378), which can be isolated in a few cases. The dimerization of the hydrazones proceeds at room temperature and is catalyzed by acids. As mentioned above, protonation affords the intermediate (379) which dimerizes to yield (377 R1 = H). 

Recently, several syntheses of pyridazines from monosaccharides have been described. Calcium 2,5-diketo-D-gluconate reacts with monosubstituted hydrazines to give the corresponding pyridazinium derivatives of the zwit-terionic type 95. ° The reaction proceeds by hydrazone formation, dehydration, decarboxylation, and cyclization. In a similar manner, other... 

Saccharide hydrazones are prepared by treating aldoses, ketoses, al-dosuloses, or reducing disaccharides with unsubstituted hydrazine 81 82 with monosubstituted hydrazines having alkyl,81 acyl,30-83 84 aroyl85 sul-fonyl,36,39-40,86 8 aryl,89-93 or disubstituted tyiV-dialkyl-,81 AUY-diaryl-,94 or... 

The treatment of conjugated azoalkenes with p-diesters or p-esterphosphonates possessing two active hydrogen atoms produces, by means of the usual preliminary hydrazone intermediates, the unusual 3-monosubstituted 1-amino-lf/-pyrrol-2(3W)-ones, as discussed above 94SC453,94CJC2305. ... 

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