Reactions of sulfur monochloride with some aromatic aldehyde semicarbazones and thiosemicarbazones: New syntheses of substituted 2,4-dihydro-1,2,4-triazol-3-ones, 2,4-dihydro-1,2,4-triazole-3-thiones and 2-amino-1,3,4-oxadiazoles

Treatment of various substituted semicarbazones of aromatic aldehydes with sulfur monochloride yields the corresponding substituted 2,4-dihydro-1,2,4-triazol-3-ones. With thiosemicarbazones, the products are derivatives either of the 2-amino-1,3,4 thiadiazole or of the 2,4-dihydro-1,2,4-triazole-3-thione depending on the experimental conditions.     

Cascade synthesis of substituted 4-amino-1,2,4-triazol-3-ones from aldehyde hydrazones and azodicarboxylates

Substituted 4-amino-1,2,4-triazol-3-ones were synthesized from aldehyde hydrazones and azodicarboxylates in the presence of triphenylphosphine. The cascade reaction was conducted in a single step and the procedure is general and efficient.     

Ultrasound-assisted synthesis of 2-amino-1,3,4-oxadiazoles through NBS-mediated oxidative cyclization of semicarbazones

A ultrasound-assisted oxidative cyclization of semicarbazones using N-bromosuccinimide in the presence of sodium acetate was established providing efficient and rapid access to a variety of 2-amino-1,3,4-oxadiazoles. Moreover, the new synthetic protocol provides a simple procedure utilizing a safer oxidizing system that affords the target products in high regioselectivity, satisfactory yields, and elevated purities.     

Synthesis of new derivatives of 4-amino-2,4-dihydro-1,2,4-triazol-3-one as potential antibacterial agents

Thirty new 2-substituted-4-amino-5-alkyl or aryl-2,4-dihydro-1,2,4-triazol-3-ones and ten 2-substituted-5-alkyl or aryl-4-(5-nitro-2-furfurylidene)amino-2,4-dihydro-1,2,4-triazol-3-ones were synthesized and characterised by their sharp melting points, elemental analysis, ir and ¹H nmr spectra. These new derivatives of 5-nitro-2-furaldehyde were screened for their antibacterial activities. Most of the compounds showed good activity against one test organism, Staphylococcus aureus. For a few compounds, C.M.I. ranged from 4 to 8 μg/ml (higher results than nitrofurantoin).     

Conformational analysis of 2,5-diaryl-4-methyl-2,4-dihydro-3H-1,2,4-triazol-3-ones: Multinuclear NMR and DFT calculations

Conformational exploration of five 2,5-diaryl-4-methyl-2,4-dihydro-3H-1,2,4-triazol-3-ones has been carried out based on a combination of their NMR chemical shifts determined in CDCl₃ and the scrutiny of their computed relative energies and absolute shieldings calculated at the DFT/GIAO/B3LYP/6–311++G(d,p) level. The very flat potential energy curves corresponding to the three relevant single bond rotations were explored by calculating the energy of the rotational barriers and comparing the experimental chemical shifts with those theoretically calculated in each rotamer by statistical analysis.     

Conversion of 2-amino-5-R-phenyl-1,3,4-oxadiazoles into 3-R-phenyl-5-alkoxy-1,2,4-triazoles

2-Amino-5-R-phenyl-1,3,4-oxadiazoles have been shown to isomerize in alcoholic potassium hydroxide solution to 3-R-phenyl-5-alkoxy-1,2,4-triazoles. The dissociative ionization of 3-R-phenyl-5-alkoxy-1,2,4-triazoles and 3-R-phenyl-1,2,4-triazolin-5-ones has been examined. The mass spectra of the oxadiazoles have been compared with those of the triazoles.Translated from Khimiya Geterotslklicheskikh Soedinenii, No. 11, pp. 1553–1556, November, 1986.     

Picryl derivatives of 5-nitro-2,4-dihydro-3H-1,2,4-triazol-3-one

Treatment of 5-nitro-2,4-dihydro-3H-1,2,4-triazol-3-one ( 1 ) with picryl fluoride (PkF) in 1-methyl-2-pyrrolidinone (NMP) gave a mixture of a monopicryl and a dipicryl derivative of 1 in a ratio of 2 :1 , respectively, regardless of the initial concentrations of 1 and PkF. The products were identified as 5-nitro-2-picryl-2,4-dihydro-3H-1,2,4-triazol-3-one ( 2 ) by X-ray crystallography and 5-nitro-2,4-dipicryl-2,4-dihydro-3H-1,2,4-triazol-3-one ( 4 ) by ¹⁵N labeling experiments.     

Kinetics of 2,4-dihydro-1,2,4-triazol-3-one nitration in nitric acid

The kinetics and mechanism of 2,4-dihydro-1,2,4-triazol-3-one nitration in nitric acid have been studied. The role of 2-nitro-2,4-dihydro-1,2,4-triazol-3-one as an intermediate has been determined.     

Synthesis of 2-amino-5-(5R-1,2,4-oxadiazolyl-3)-1,3,4-oxadiazoles

The interaction of 2-amino-1,3,4-oxadiazole-5-carboxamidoxime with nitriles in the presence of ZnCl₂ and HCl or with trichloroacetic anhydride affords 2-amino-5-(5R-1,2,4-oxadiazolyl-3)-1,3,4-oxadiazoles. Their reactions with N-nucleophiles have been studied.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2100–2103, December, 1993.     

Optimization of the synthesis of 5-amino-1,2,4-triazol-3-ylacetic acid and bis(5-amino-1,2,4-triazol-3-yl)methane

The influence of the molar ratio and concentration of the reactants and of the temperature and time of the synthesis on the yield of malonic acid guanylhydrazides in the reaction of aminoguanidine with malonic acid in acidic aqueous solutions was examined, and improved procedures for preparing 5-amino-1,2,4-triazol-3-ylacetic acid and bis(5-amino-1,2,4-triazol-3-yl)methane were suggested.     

Uncatalyzed synthesis of 3-amino-1,5-dihydro-2H-pyrrol-2-ones

Uncatalyzed one-pot pseudo-four-component reaction of ethyl pyruvate, anilines, and aldehydes in n-hexane as solvent, under reflux, affords a variety of 3-amino-1,5-dihydro-2H-pyrrol-2-ones in high yield. n-Hexane is an excellent driving force in preparation of the desired products. These compounds have biological and pharmacological properties and are also used in medicinal chemistry. Use of a non-toxic and inexpensive solvent, simple and efficient synthesis, clean work-up, and high yields of the products are the advantages of this method. We report the first catalyst-free method for synthesis this class of compounds.     

Synthesis and properties of azoles and their derivatives. 36. Synthesis of 2-amino-1,3,4-oxadiazoles, 2-amino-1,3,4-thiadiazoles,and 1,2,4-triazoline-3-thiones containing indolyl radicals

On the heterocyclization of 1-(indol-3-ylcarbonyl)thiosemicarbazides, depending on the conditions of performing the reaction, either 1,2,4-triazoline-3-thiones, 2-amino-1,3,4-thiadiazoles, or 2-amino-1,3,4-oxadiazoles containing an indolyl residue in position 5 are obtained. 1,2,4-Triazoline-3-thiones and 2-amino-1,3, 4-thiadazoles have also been synthesized by the reaction of the hydrochloride of ethyl indol-3-carboximidate with thiosemicarbazides.For communication 35, see [1].Translated from Khimiya Geterotsilicheskikh Soedinenii, No. 9, pp. 1271–1276, September, 1984.     

Aroylation of 5-amino-2H-1,2,4-thiadiazolin-3-ones

2-Aroyl-5-aroylamino-1,2,4-thiadiazolin-3-ones ( 2 ) have been synthesized through aroylation of 5-arruno-2H-1,2,4-thiadiazolin-3-one ( 1 ) as an analog of cytosine. The aroylation was carried out with a substituted aroyl chloride in pyridine at 56～58°C. It has been established that the intermediates of the reactions are 2-aroyl-5-amino-1,2,4-thiadiazolin-3-ones ( 3 ) on the basis of the spectral data, additional experimental information and ab initio molecular orbital calculations.     

Oxidation and acid-catalyzed cyclization of aldehyde 2-aminophenylhydrazones. Alternative syntheses for 1,2,4-benzotriazines and benzimidazoles

Aldehyde 2-aminophenylhydrazones are easily oxidized by air to 3-substituted 1,2,4-benzotriazines. In two cases the intermediate 3,4-dihydro-1,2,4-benzotriazines were isolated. In the absence of oxygen, acids catalyze the formation of 2-substituted benzimidazoles with loss of ammonia. It is suggested that both reactions proceed via 1,2,3,4-tetrahydro-1,2,4-benzotriazines (III), formed by addition of the amino group on the hydrazone double bond. Such cyclic forms (III) predominate over the open chain structures (II) in the cases of aliphatic and arylalkylaldehyde 2-aminophenylhydrazones, as supported by nmr spectra, while benzaldehyde 2-aminophenylhydrazone exists mainly or exclusively in the open chain form (II).     

Manipulation of N,O-nucleophilicity: efficient formation of 4-N-substituted 2,4-dihydro-3H-1,2,4-triazolin-3-ones

A new efficient two-step synthesis of 2,4-dihydro-3H-1,2,4-triazolin-3-ones (triazolinones) from readily available amines is reported. Our novel conditions using hexamethyl disilazane, bromotrimethylsilane, and a catalytic amount of ammonium sulfate smoothly cyclize 1-formyl and 1-acetyl semicarbazides to the target triazolinones. This transformation features simultaneous manipulation of N- and O-nucleophilicity as well as differentiation of the nucleophilicity of a urea and an acyl carbonyl.     

Synthesis of esters and amides of 5-amino-1,2,4-triazole-3-carboxylic and 5-amino-1,2,4-triazol-3-ylacetic acids

Various synthetic routes to esters and amides of 5-amino-1,2,4-triazole-3-carboxylic and 5-amino-1,2,4-triazol-3-ylacetic acids were examined.