Tautomerism in 3-ethoxy-5-phenyl-1,2,4-triazole

The cmr spectrum of the title compound was observed at several temperatures and assigned based on a tautomeric exchange requiring that the N(1)-H compound be present to the extent of 70%.     

Tautomerism of 1,2,4-triazino[2,3-a]benzimidazol-5(4)H-3-ones

Studies by X-ray diffraction and quantum chemical methods demonstrated that 1,2,4-triazino[2,3-a]benzimidazol-5(4)H-3-ones exist in the condensed state primarily in the 5H-tautomeric form, whereas these compounds exist, most likely, predominantly as 4H tautomers in the gas phase. The low-barrier tautomerism of 1,2,4-triazino[2,3-a]benzimidazol-5(4)H-3-ones occurs through the intermediate formation of hydrogen-bonded cyclic dimers followed by the concerted two-proton transfer. N-Alkylation of both the electroneutral and N-anionic forms of 2-methyl-1,2,4-triazino[2,3-a]benzimidazol-5(4)H-3-one affords predominantly N(4)-alkyl derivatives. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 475–483, March, 2006.     

X-Ray Diffraction Study of 8-(Pyridin-2-yl)- and 8-(1,2,4-Triazin-5-yl)-2H-chromen-2-ones

Russian Journal of General Chemistry - The molecular and crystal structures of 8-(3,6-diphenylpyridin-2-yl)-5,7-dimethoxy-4-phenyl-2H-chromen-2-one,...     

Prototropic Tautomerism in Phosphoryl-Hydroxyylide and Thiophosphoryl-Mercaptoylide Systems

Abstract

Two new types of tautomerism are discussed: phosphoryl-hydroxyylide and thiophosphoryl-mercaptoylide tautomerism.     

5-取代苯氨基-6-苯基-1,2,4-三嗪-3-酮的合成

苯甲铣基-N-取代茜基硫代甲酰胺与氨基脲缩合后,环化可何成4,6-二取代-5-硫酮-1,2,4-三嗪-3-酮.本文报道将其缩氨基脲中硫甲基化,然后在碱性条件下, 改变成环方式,合成九个5-取代苯氨基-6-苯基-1,1,4-三嗪1-3-酮.它们的结构经元素分析,红外,核磁,质谱等予以证实.探讨了两种不同成环原因.     

Δ3- and Δ4-1,2,4-oxadiazolin-5- and 3-ones

Preparations for 2,3-diphenyl- and 2-benzyI-3-phenyl-Δ³-1,2,4-oxadiazolin-5-ones (3) and (4) and for 2,5-diphenyl-Δ⁴-1,2,4-oxadiazolin-3-one ( 7 ) are reported.     

Tautomerism and Acid-Base Properties of Formyl Derivatives of 1-Phenyl-3-methyl-4,5-dihydropyrazol-5-one and Its Thio Analog

A single-crystal X-ray diffraction study showed that 1-phenyl-3-methyl-4-formyl-4,5-dihydropyrazol-5-one occurs in the solid phase as two conformers of the NH tautomer. The acidity and basicity constants of 1-phenyl-3-methyl-4-formyl-4,5-dihydropyrazol-5-one and its analog, -5-thione, in 50% aqueous dioxane were measured. PM3 calculations qualitatively explan the differences in the tautomerism and acid-base properties of 4-formylpyrazolone (-pyrazolethione) and the corresponding compounds without the formyl substituent.     

ab Initio Calculation on Tautomerism of Pyrazolin—5—ones

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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.     

Efficient synthesis of 5-substituted-4,5-dihydro-1,2,4-triazin-6-ones and 5-substituted-1,2,4-triazin-6-ones

Treatment of methyl α-(dimethylarninomethyleneamino)carboxylates 1 (from α-amino acids and dimethylformamide dimethylacetal) with hydrazine gives 5-substituted-4,5-dihydro-1,2,4-triazin-6-ones 2 , which are smoothly dehydrogenated to 5-substituted-1,2,4-triazin-6-ones 3 with potassium permanganate in acetone/acetic acid.     

Cycloaddition-elimination reactions of 5-imino-1,2,4-dithiazolidin-3-ones with heterocumulenes

5-Benzylimino-1,2,4-dithiazolidin-3-one ( 2a ) reacts with heterocumulenes (isocyanates, isothiocyanates, ketenes) with elimination of carbonyl sulfide, yielding the heterocycles 6–8 . The thiadiazolidine 6a , obtained from 2a and phenyl isocyanate, underwent similar reactions but under milder conditions, indicating that phenyl isocyanate is a better leaving group than carbonyl sulfide.     

Synthesis and properties of 5-aroylamino-2H-1,2,4-thiadiazol-3-ones

5 -Aroylamino-2H-1,2,4-thiadiazol-3-ones 3 were obtained from the corresponding 1-aroyl-2-thiobiurets 2 by oxidative cyclization with bromine. 5 -Aroylamino-2H-1,2,4-thiadiazol-3-ones 3 can exist in two tautomeric forms a lactam form and a lactim form. On the basis of the ¹³C nmr spectra and additional experimental information, it has been established that the stable form, in which these compounds exist, is the lactam form.     

Azomalonate Syntheses Part II. Synthesis and Reactivity of Novel 1,2,4-Triazin-5-one Derivatives

Base treatment of azomalonates derived from N-substituted dialkyl (2-chloroacetamido)malonates results in the formation of 4-substituted alkyl 5-oxo-1,4,5,6-tetrahydro-1,2,4-triazine-3-carboxylates. The same malonates coupled with diazotized 2-amino-5-chlorobenzophenone or methyl anthranilate afford triazinones which can be cyclized into novel triazino[1,6-a]indoles. Two representative heterocycles are further characterized by typical reactions. Whereas oxidation gives the corresponding triazine-5,6-diones, the outcome of the reduction is strongly dependent on the nature of the substituent at C(4). Bromination followed by aqueous workup leads to the 6-hydroxy derivatives. Some mechanistic aspects of this novel triazinone synthesis are discussed.     

Adamantylation of 3-Nitro- and 3-Ethoxycarbonyl-1,2,4-triazolo[5,1-c]-1,2,4-triazin-4-ones

Reaction of 3-nitro- and 3-ethoxycarbonyl-1,2,4-triazolo[5,1-c]-1,2,4-triazin-4-ones with 1-adamantanol (or 1-adamantyl nitrate) in concentrated sulfuric acid or with 1-bromoadamantane in sulfolane affords N-adamantyl derivatives. The adamantylation of 3-nitro-1,4-dihydro-7H-1,2,4-triazolo[5,1-c]-1,2,4-triazin-4-one yields a mixture of N⁸- and N¹-isomers that undergo interconversion in concentrated sulfuric acid along intermolecular mechanism.     

The Synthesis of 1,2,4-Trioxan-5-ones

Several 3,6-substituted 1,2,4-trioxan-5-ones have been prepared in good yield by condensing aldehydes and ketones with trimethylsilyl α-[(trimethylsilyl)peroxy]alkanoates in the presence of trimethylsilyl trifluoromethane sulfonate as catalyst.     

Synthetic and spectroscopic study of 5-amino-2-acyl-1,2,4-thiadiazolin-3-ones

5-Amino-2-acyl-1,2,4-thiadiazolin-3-ones 2–1 can be synthesized from 5-amino-2H-1,2,4-thiadiazolin-3-one ( 1–1 ) via a selective acylation with an acid anhydride in pyridine. The ¹H nmr spectral characteristics of 5-amino-2-acyl-1,2,4-thiadiazolin-3-ones 2–1 is in particular, compared with 5-amino-2H-1,2,4-thiadiazolin-3-one ( 1–1 ) and 5-amino-2-alkyl-1,2,4-thiadiazolin-3-ones 1–2, 1–3 . The 5-amino group of 2–1 appeared as two peaks in its ¹H nmr spectrum, which merged to a single peak at a higher temperature, while those of compound 1–1, 1–2 and 1–3 appear only as a single peak. The restricted rotation of the C(5)-N(5) (at amino) bond of 5-amino-2-acetyl-1,2,4-thiadiazolin-3-one (2a-1) is about 14.5 Kcal/mol.     

Chlorination of isothiocyanates. V . 5-imino-1,2,4-thiadiazolidin-3-ones

S-[N'- (Chlorocarbonyl)amino]isothiocarbamoyl chlorides (II), obtained from S-chloroisothiocarbamoyl chlorides (I) and isocyanates, react with primary aliphatic and aromatic amines to form the unknown class of 5-imino-1,2,4-thiadiazolidin-3-ones. The structures were confirmed by chemical means and by spectroscopic methods.     

A Quantum-Chemical Study of Prototropic Tautomerism in 1-Hydroxy-9,10-anthraquinones

The effect of substituents R on the tautomerism and electronic absorption spectra of 1-hydroxy-x-R-9,10-anthraquinones and 9-hydroxy-x-R-1,10-anthraquinones was studied by quantum-chemical and correlation methods. The former compounds (x 2) are more sensitive to substituent effects than the latter compounds. Examination of the fine structure of long-wave absorption showed that the experimental spectra of 1-hydroxy-x-R-9,10-anthraquinones contain no bands assignable to ana-quinoid forms.     

Study of Tautomerism in Some β-Keto Phosphoryl Prototropic Pentad Systems

Abstract

By the reaction of phosphoryl substituted acylmethylenetriphe-nylphosphoranes (I, II) with hydrogen halides prototropic pentad tautomeric systems (III, IV) have been obtained.