K. N. Zelenin

Amidrazones in the synthesis of heterocycles (review)

Data on the synthesis, on the basis of amidrazones, of mono-, di-, tri-, and tetrazoles, diazoles containing boron, oxygen, silicon, phosphorus, and sulfur atoms in the ring, mono-, di-, tri-, and tetrazines, triazepines, and benzotriazepines, as well as a number of condensed heterocyclic derivatives, are systematized.

Ring-chain isomerism (tautomerism) of functionally substituted hydrazones (review)

The known data on the ring-chain tautomerism (isomerism) of hydrazones with functional substitutents in the alkylidene or hydrazine fragment of the molecules are systematized. The structural factors and conditions that determine the reversible conversion of the corresponding linear derivatives to representatives of heterocycles — isoindole, tetrahydrofuran, pyrazole, isoxazole, 1,2,4-triazole, 1,3,4-thiadiazole, 1,3,4-oxadiazine, 1,2,4-triazine, 1,3,4-thiadiazine, 1,2,4,5-tetrazine, etc. — are correlated.

Synthesis of pyrazole, 1,3,4-thiadiazole, and 1,2,4-triazole derivatives by condensatoin of 1,3-dioxo compounds with thiosemicarbazide derivatives

The reaction of β-diketones with 2-unsubstituted thiosemicarbazides leads to the formation of the corresponding 1-thiocarbamoyl-5-hydroxy-2-pyrazolines, which readily undergo aromatization to give pyrazoles, while the reaction of benzoylacetaldehyde leads to the formation of the corresponding hydrazone. Acetylacetone 2-methyl- and 2,4-dimethylthiosemicarbazones are inclined to undergo tautomerization and, depending on the conditions, can exist in enehydrazine, hydrazone, 1,2,4-triazoline, and 1,3,4-thiadiazoline forms or mixtures of these forms. Upon heating these substances are converted to mixtures of the 1,3,5-trimethylpyrazole and the corresponding 1,2,4-triazoline-5-thione. The structures of the compounds were studied by means of IR and 1H, 13C, and 15N NMR spectroscopy and mass spectrometry.

Synthesis of isoxazolidine derivatives from N-substituted hydroxylamines and α,Β-unsaturated ketones

The reaction of methyl vinyl ketone with N-Phenyl-hydroxylamine leads to a tautomeric mixture of 5-hydroxy-2-phenyl-5-methylisoxazolidine and its linear form, while the reaction with benzohydroxamic acid leads to linear products of addition to the oxygen or nitrogen atoms, depending on the reaction conditions. The first representatives of 5-hydroxyisoxazolidines with the residue of an aliphatic carboxylic acid attached to the nitrogen atom were obtained by acylation of 5-hydroxy-3,3,5-trimethylisoxazolidine.

Synthesis and structure of 1-methyl-2,3-dihydro-1,2,4-triazolium salts and their free bases

Abstract1-Methyl-2,3-dihydro-1,2,4-triazolium iodides can be obtained by reacting methylhydrazones with S-methylthioamide hydriodides, by condensing 2-methylamidrazone hydriodides with aldehydes and ketones, or by reacting methyl iodide with 1-alkylidene (or arylidene)benzamidrazones. In solutions these salts are capable of undergoing tautomerism to 1-alkylidene(or arylidene)-2-methylamidrazone hydriodides. The influence of the structural factors on the position of the tautomeric equilibrium has been studied. The free bases obtained by neutralization of the respective salts by an alkali metal hydroxide are heretofore undescribed 1-alkylidene(or arylidene)-2-methylhydrazidoimines or 4-triazolines, depending on their structure. Under the action of oxygen, these compounds are readily oxidized to substituted 1-methyl-1,2,4-triazoles with heating.

RING-RING TAUTOMERISM

The superposition within a single molecule of competing ring-chain tautomeric pairs, the minimum structural requirement of which is the presence of one nucleophilic (OH, NH, SH, etc.) and two electrophilic (C=N, C=O, etc.) centers or the reverse, is a method of constructing ring-ring or ring-chain-ring tautomeric systems. On the basis of the structural characteristics of alkylidene derivatives of thiohydrazides, thiosemicarbazides, thiocarbonohydrazides and amidrazones, bis-hydrazones, bis-oximes, and oximohydrazones of 1,3-dioxo compounds, it has been possible to realize for the first time heterocyclic, tautomeric combinations of pyrazoline—isoxazoline, isoxazoline—1,3,4-thiadiazoline, pyrazoline—1,3,4-thiadiazoline, 1,3,4-thiadiazoline-1,2,4-triazolidene, 1,2,4-triazolidene—1,2,4,5-hexahydrotetrazine, 1,2,4,5-hexahydrotetrazine—tetrahydropyran, tetrahydropyran—1,3,4-thiadiazoline, etc.

Synthesis and structure of 5-hydrazino- and 5-hydroxyamino-3-aryl-2-pyrazolines and-2-isoxazolines

It was established by the methods of 1H and 13C NMR spectroscopy that the oximohydrazones and bis(hydrazones) of aroylacetic aldehydes exist in the form of the corresponding 5-hydrazino- and 5-hydroxyamino-3-aryl-2-pyrazolines and -2-isoxazolines. The features of the aromatization of these compounds to the corresponding pyrazoles and isoxazoles were studied. Data on the mass-spectral study of the 5-hydroxyamino-2-pyrazoline-5-hydrazino-2-isoxazoline tautomerism in the gas phase are presented.

5-Hydrazino-2-pyrazolines

Abstract1-Acyl-5-hydrazino-2-pyrazolines have been obtained by reaction of the appropriate hydrazines with aliphatic 1,3-diketones, 1-acyl-5-hydroxy-2-pyrazolines, and 1-acyl-5-methylene-2-pyrazolines. The latter were synthesized by acylating 3,4,4,5-tetramethyl-4H-pyrazole with carboxylic anhydrides. The structures of the products were established by 1H and 13C NMR spectroscopy and mass spectrometry.

Synthesis of 5-hydroxy- and 5-acylhydrazinopyrazolidines by the reaction of ?-substituted hydrazides with ?,?-unsaturated aldehydes and their biological activity

The reaction of β-substituted hydrazides with alkenals (acrolein, methacrolein, crotonaldehyde, and cinnamaldehyde) serves as a method for the synthesis of the corresponding 1-acyl-5-hydroxypyrazolidines and, in a number of cases, 1-acyl-5-acylhydrazinopyrazolidines. Some of the 1-acyl-5-hydroxypyrazolidines obtained have antiphlogistic activity.

2-phenyl-1,3,4-thiadiazol-2-ines

According to data from the1H and13C NMR spectra in nonpolar media and the mass spectra, alkylidene derivatives of thiobenzhydrazide have a 1,3,4-thiadiazol-2-ine structure rather than a thiobenzhydrazone structure. The products of condensation of thiobenzhydrazide with acetone and anisaldehyde in methanol undergo partial isomerization to thiobenzhydrazones. The hydrochlorides of the compounds under discussion are the corresponding 1,3,4-thiadiazolinium salts, in which the proton is coordinated with the N4, atom. The 2-phenyl-5,5-dimethyl-1,3,4-thiadiazol-2-ine anion has a noncyclic thioenolate structure.