Synthesis and Chemical Transformations of 5-Alkyl(phenyl)-4,5,6,7-tetrahydro[1,2,4]triazolo[1,5-<Emphasis Type="Italic">a</Emphasis>]pyrimidin-7-oles

5,5,7-Trimethyl-4,5,6,7-tetrahydro[1,2,4]triazolo[1,5-a]pyrimidin-7-ol was synthesized by cyclocondensation of 3-amino-1,2,4-triazole with 4-methylpent-3-en-2-one; its chemical transformations, and also the transformations of 5-phenyl-4,5,6,7-tetrahydro[1,2,4]triazolo[1,5-a]pyrimidin-7-ol were investigated in reactions with reagents of diverse electronic nature.     

2-Methylthio-4,5,6,7-tetrahydro-1,2,4-triazolo[1,5-<Emphasis Type="Italic">a</Emphasis>]pyrimidin-5- and -7-Ones

The cyclocondensation of methylcinnamates and arylidene derivatives of Meldrums acid with 3-amino-5-methylthio-1,2,4-triazole in DMF gives 2-methylthio-4,5,6,7-tetrahydro-1,2,4-triazolo[1,5-a]-pyrimidin-5-ones. The reaction involving arylidene derivatives of Meldrums acid or its synthetic equivalents in ethyl acetate with a catalytic amount of pyridine gives a mixture of 2-methylthio-4,5,6,7-tetrahydro-1,2,4-triazolo[1,5-a]pyrimidin-5- and -7-ones.__________Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 246–251, February, 2005.     

Fluorinated [1,2,4]triazolo[1,5-<Emphasis Type="Italic">a</Emphasis>]pyrimidines and [1,2,4]triazolo[5,1-<Emphasis Type="Italic">c</Emphasis>][1,2,4]triazines*

The reaction of 3-R-5-amino-1,2,4-triazoles with the ethyl ester of 2-fluoroacetoacetic acid gave 2-R-fluoro[1,2,4]triazolo[1,5-a]pyrimidin-7(4H)-ones. The reaction of a 3-R-1,2,4-triazolyl-5-diazonium salt with the ethyl ester of 2-fluoroacetoacetic acid and subsequent cyclization of the triazolylhydrazones lead to 7-R-3-fluoro[1,2,4]triazolo[5,1-c][1,2,4]triazin-4(1H)-ones.     

Synthesis of new 4-(4,5-diphenyl-1h-imidazol- 2-yl)tetrazolo[1,5-<Emphasis Type="Italic">a</Emphasis>]quinolines from tetrazolo[1,5-<Emphasis Type="Italic">a</Emphasis>]quinolines

Some new 4,5-diphenyl-1H-imidazole derivatives were synthesized in good yields by treating various tetrazolo[1,5-a]quinolines with benzil and ammonium acetate in glacial acetic acid.     

A regio- and stereoselective three-component synthesis of 5-(trifluoromethyl)-4,5,6,7-tetrahydro-[1,2,4]triazolo[1,5-<Emphasis Type="Italic">a</Emphasis>]pyrimidine derivatives under solvent-free conditions

An efficient one-pot method for regio- and stereoselective synthesis of 5-(trifluoromethyl)-4,5,6,7-tetrahydro-[1,2,4]triazolo[1,5-a]pyrimidines under solvent-free and catalyst-free conditions has been developed. The method involves employing a three-component condensation reaction of an aromatic aldehyde and ethyl 4,4,4-trifluoro-3-oxobutanoate or 1,1,1-trifluoropentane-2,4-dione in the presence of 1,2,4-triazol-3-amine at 90°C.     

A new approach to synthesis of 2-sulfonylamino-1,2,4-triazolo[1,5-<Emphasis Type="Italic">a</Emphasis>]pyrimidines

A procedure for synthesis of 2-sulfonylamino-1,2,4-triazolo[1,5-a]pyrimidines by sulfonylation of 2-amino-4,7-dihydro-1,2,4-triazolo[1,5-a]pyrimidines, followed by oxidation of intermediate 2-sulfonylamino-4,7-dihydro-1,2,4-triazolo[1,5-a]pyrimidines, was suggested.     

Synthesis of pyrazolo[4,3-<Emphasis Type="Italic">e</Emphasis>][1,2,4]triazolo[4,3-<Emphasis Type="Italic">c</Emphasis>]pyrimidines

Starting from 1,5-dihydro-4H-pyrazolo[3,4-d]pyrimidin-4-ones, a synthesis pathway to the tricyclic pyrazolo[4,3-e][1,2,4]triazolo[4,3-c]pyrimidines is described. Reaction of 1,5-dihydro-4H-pyrazolo[3,4-d] pyrimidin-4-ones with phosphoryl chloride afforded the corresponding 4-chloro-1H-pyrazolo[3,4-d]pyrimidines. Treatment of these compounds with hydrazine hydrate at reflux temperature gave the hydrazino derivatives, which were subsequently cyclized to the titled compounds on heating with orthoesters in ethanol. Correspondence: Abolghasem Davoodnia, Department of Chemistry, School of Sciences, Islamic Azad University, Mashhad Branch, Mashhad 91735-413, Iran.     

Fluoro-containing Heterocycles: XIII. Fluoro-containing Derivatives of Thiazolo[3,2-<Emphasis Type="Italic">a</Emphasis>]-, Benzothiazolo[3,2-<Emphasis Type="Italic">a</Emphasis>]-, and Benzimidazo[3,2-<Emphasis Type="Italic">a</Emphasis>]quinazolinones

Reactions of 2-aminothiazole, derivatives of 2-aminobenzothiazole and 2-aminobenzoimidazole with polyfluorobenzoyl chlorides gave rise to acylation products that at heating in the diphenyl ether formed fluoro-containing derivatives of thiazolo[3,2-a]-, benzothiazolo[3,2-a]-, and benzimidazo[3,2-a]quinazolinone.     

Synthesis of derivatives of pyrazolo[1,5-<Emphasis Type="Italic">a</Emphasis>]pyrimidines and imidazo[1,5-<Emphasis Type="Italic">a</Emphasis>]pyrimidines proceeding from alkyl 2-benzylidene-3-oxo-3-fluoroalkylpropionates

Methods were developed of the synthesis of alkyl 2-hydroxy-2-fluoroalkyl-4-phenyl-1,2,3,4—tetrahydroimidazo-[1,5-a]pyrimidine-3-carboxylates and alkyl-5-hydroxy-2,7-diphenyl-5-fluoroalkyl-4,5,6,7-tetrahydropyrazolo[1,5-a]pyrimidine-6-carboxylates by regioselective [3+3]-cycloaddition of 5-aminoimidazole or 5-aminopyrazole to alkyl 2-benzylidene-3-oxo-3-fluoroalkylpropionates at the fluoroacylvinyl fragment.     

Cycloalkaneindoles with 2-trifluoromethylimidazo[1,2-<Emphasis Type="Italic">a</Emphasis>]pyridin-6-yl fragment

Modification of biologically active cycloalkaneindoles by incorporation of a 2-trifluoromethylimidazo[1,2-a]pyridin-6-yl fragment has been proposed and performed via the interaction with 3-fluoro-2-trifluoromethylimidazo[1,2-a]pyridines in the presence of potassium hydroxide. The action of the prepared compounds on neuronal NMDA receptors has been studied by means of radioligand binding.     

Synthesis and biological activity of 3-guanidino-6-R-imidazo[1,2-<Emphasis Type="Italic">b</Emphasis>]- and 6-guanidino-3-R-[1,2,4]triazolo[4,3-<Emphasis Type="Italic">b</Emphasis>][1,2,4,5]tetrazines

The reaction of azoloannulated [1,2,4,5]tetrazines with guanidine was studied. New 3-guanidinoimidazo[1,2-b]- and 6-guanidino[1,2,4]triazolo[4,3-b] [1,2,4,5]tetrazines were synthesized using the nucleophilic substitution methodology. Compounds with high antibacterial and antiglycation activity were revealed.     

Synthesis of alkyl 5-aryl-7-methyl-1,5-dihydrotetrazolo-[1,5-<Emphasis Type="Italic">a</Emphasis>]pyrimidine-6-carboxylates

Alkyl 5-aryl-7-methyl-1,5-dihydrotetrazolo[1,5-a]pyrimidine-6-carboxylates were obtained by melting acetoacetic acid esters with 5-aminotetrazole and aromatic aldehyde.     

Synthesis of substituted 4-([1,2,4]triazolo[3,4-<Emphasis Type="Italic">b</Emphasis>]-[1,3,4]thiadiazol-6-yl)quinolines

4-Amino-5-R¹-4H-1,2,4-triazole-3-thiols react with 2-R²-6-R³-quinoline-4-carboxylic acids in phosphoryl chloride to give 2-R²-6-R³-4-(3-R¹-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazol-6-yl)quinolines.     

Synthesis of azepino[1,2-<Emphasis Type="Italic">a</Emphasis>]benzimidazoles and imidazo[1,2-<Emphasis Type="Italic">a</Emphasis>]azepines

Fusion of 4-bromo-1,3-diphenyl-2-buten-1-ones (γ-bromodypnones) with 1,2-dimethyl-1H-benzimidazole and further treatment of the reaction product with a base (morpholine) gives 7,9-diaryl-5-methyl5,10-dihydroazepino[1,2-a]benzimidazol-11-ium bromides. The reaction of γ-bromodypnone with 1-alkyl-2-methyl-1H-imidazoles in benzene at 25 °C gives quaternary azolium salts. Upon heating their solutions in alcohol in the presence of K₂CO₃ the latter cyclize to 1-R-6,8-diaryl-1,5-dihydroimidazo[1,2-a]azepin-4-ium bromides or 1-R-6,8-diaryl-1H-imidazo[1,2-a]azepines depending on the nature of the substituent in the benzene rings and the substituent at the N(1) atom of the imidazole.     

2-amino-4,5,6,7-tetrahydro-1,2,4-triazolo[1,5-<Emphasis Type="Italic">a</Emphasis>]pyrimidines: Synthesis and reactions with electrophilic reagents

The hydrogenation of 2-amino-5-R-7-R′-4,7-dihydro-1,2,4-triazolo[1,5-a]pyrimidines with NaBH₄ led to the formation of 2-amino-5-R-7-R′-4,5,6,7-tetrahydro-1,2,4-triazolo[1,5-a]pyrimidines. Acylation, sulfonylation, and alkylation of these compounds depending on conditions and the reagent character occur at the amino group, atoms N³ or N⁴. The treatment with alkali of 2-amino-3-benzyl-5-R-7-R′-4,5,6,7-tetrahydro-1,2,4-triazolo-[1,5-a]pyrimidinium bromide resulted in 2-amino-3-benzyl-5-R-7-R′-3,5,6,7-tetrahydro-1,2,4-triazolo[1,5-a]-pyrimidine, similar reaction of 2-acetamido-3-benzyl-5-R-7-R′-4,5,6,7-tetrahydro-1,2,4-triazolo[1,5-a]-pyrimidinium bromide gave a mesoionic product of a hydrogen elimination from the amide nitrogen atom.     

Synthesis and X-ray study of 6<Emphasis Type="Italic">H</Emphasis>-chromeno[3,4-<Emphasis Type="Italic">e</Emphasis>][1,3,4]triazolo[2,3-<Emphasis Type="Italic">a</Emphasis>]pyrimidine

2-Dimethylamino methylenechromanone 1 reacted with 4H-1,2,4-triazol-3-amine in acetic acid to give only one isolated product which was identified by X-ray study as 6H-chromeno[3,4-e][1,3,4]triazolo[2,3-a]-pyrimidine. The molecular structure of 3, C₁₂H₈N₄O, was determined to be monoclinic, P2₁/c, a = 16.3875(5), b = 8.8378(3), c = 13.8392(5) Å, β = 101.190(1)°, V = 1966.22(11) ų, Z = 8.     

Corrosion Inhibition of Mild Steel in Acidic Solutions Using 1,2,4-Triazolo[1,5-<Emphasis Type="Italic">a</Emphasis>]pyrimidine

The inhibiting action, thermodynamics, and adsorptive properties of 1, 2, 4-triazolo[1, 5-a]pyrimidine (TP) have been investigated for the corrosion of mild steel in 0.5 M H₂SO₄ and 0.5 M H₃PO₄ solutions by means of potentiodynamic, electrochemical impedance spectroscopy techniques and quantum chemical calculations. Results obtained revealed that TP is more effective in 0.5 M H₃PO₄ than in 0.5 M H₂SO₄. Theoretical fitting of different adsorption isotherms such as Langmuir, Flory–Huggins, Temkin, and the kinetic-thermodynamic models were tested. The obtained experimental data fitted all the applied adsorption isotherms except Langmuir. The thermodynamic activation parameters were calculated. The potential of zero charge was also determined using AC measurements to clarify the nature of surface charge of the mild steel in both acidic solutions. Quantum chemical parameters were calculated and explained. The data explained that the inhibition of mild steel in both acidic solutions takes place through physicochemical adsorption mechanism.     

A facile one-pot synthesis of 6,7,8,9-tetrahydrobenzo[4,5]thieno[2,3-<Emphasis Type="Italic">d</Emphasis>]-1,2,4-triazolo[4,5-<Emphasis Type="Italic">a</Emphasis>]pyrimidin-5-ones

Abstract  The reaction of 2-mercapto-6,7,8,9-tetrahydro-3H-benzo[4,5]thieno[2,3-d]pyrimidin-4-one or its 2-methylthio derivative with hydrazonoyl halides, in the presence of triethylamine, yielded 6,7,8,9-tetrahydrobenzo[4,5]thieno[2,3-d]-1,2,4-triazolo[4,5-a]pyrimidin-5-ones. The structure of the latter compounds was further confirmed by reaction of 2-mercapto-6,7,8,9-tetrahydro-3H-benzo[4,5]thieno[2,3-d]pyrimidin-4-one with the appropriate active chloromethylenes followed by coupling of the products with benzenediazonium chloride to afford the non-isolable azo-coupling products which converted, in situ, to 6,7,8,9-tetrahydrobenzo[4,5]thieno[2,3-d]-1,2,4-triazolo[4,5-a]pyrimidin-5-ones. The reaction mechanism was proposed and the products were screened for their biological activity. Some of the newly synthesized compounds had a moderate effect against some bacterial and fungal species. Graphical abstract