A facile synthesis of pyrazole-5-sulfonamide derivatives

The reaction of the 5-unsubstituted pyrazoles 2a-k with lithium diisopropylamide or n-butyllithium gave intermediary 5-lithiopyrazoles, whose reaction with sulfur dioxide afforded the lithium pyrazole-5-sulfinates 3a-k . Subsequent reaction of 3a-k with N-chlorosuccinimide followed by ammonolysis provided the pyrazole-5-sulfonamides 5a-k .     

Microwave-assisted synthesis and biological evaluation of pyrazole-4-carbonitriles as antimicrobial agents

An efficient microwave-assisted method of synthesis of pyrazole-4-carbonitriles has been developed. Condensation of pyrazole-4-carbaldehydes with hydroxylamine hydrochloride followed by reaction of the resulting oximes with the Vilsmeier-Haack reagent pre-formed from phthaloyl dichloride and dimethylformamide under microwave irradiation afforded the corresponding pyrazole-4-carbonitriles in 73% to 91% yield. The operational simplicity, avoidance of toxic reagents such as POCl₃, shorter reaction time, higher yield compared to the classical version, easy work up, and the use of the by-product in the regeneration of phthaloyl dichloride are the advantages of this methodology. All the target compounds were tested for antimicrobial activity against Gram-positive bacteria Bacillus cereus and Staphylococcus aureus; Gram-negative bacteria Escherichia coli and Yersinia enterocolitica, and the fungal species Candida albicans.     

One-pot synthesis of pyrazole-5-carboxylates by cyclization of hydrazone 1,4-dianions with diethyl oxalate

The cyclization of hydrazone dianions with diethyl oxalate afforded pyrazole-5-carboxylates.     

Unexpected Result of Thiophosphorylation of 6-Aminopyrano[2,3-c]pyrazole-5-carbonitrile Derivative

Russian Journal of General Chemistry - The reaction of 6-amino-3-methyl-4-(2,4-dichlorophenyl)-2,4-dihydropyrano[2,3-c]pyrazole-5-carbonitrile with phosphorus sulfide in boiling pyridine...     

A facile synthesis of antitumoral indeno[1,2-c]pyrazole-4-one by mild oxidation with molecular oxygen

An efficient, convenient, and general synthetic method for indeno[1,2-c]pyrazole-4-ones through oxidation of indenopyrazoles by treatment with a base and molecular oxygen is described, and a possible mechanism for the oxidation is proposed. The product indeno[1,2-c]pyrazole-4-ones were elaborated further by Suzuki coupling and Mitsunobu reaction.     

Design, synthesis, and biological evaluation of a library of 1-(2-thiazolyl)-5-(trifluoromethyl)pyrazole-4-carboxamides

A library of 422 1-(2-thiazolyl)-5-(trifluoromethyl)pyrazole-4-carboxamides was prepared in five steps using solution-phase chemistry. The first step in the synthesis was the reaction of ethyl 2-ethoxymethylene-3-oxo-4,4,4-trifluorobutanoate with thiosemicarbazide, which is reported in the literature to afford a 1:1 mixture of ethyl 1-thiocarbamoyl-5-(trifluoromethyl)pyrazole-4-carboxylate and ethyl 1-thiocarbamoyl-3-(trifluoromethyl)pyrazole-4-carboxylate. We reassigned the structure of the product to be a single compound, ethyl 5-hydroxy-1-thiocarbamoyl-5-(trifluoromethyl)-4,5-dihydro-1H-pyrazole-4-carboxylate. This common intermediate was diversified by reaction with 17 alpha-bromoketones affording, in two steps, 17 1-(2-thiazolyl)-5-(trifluoromethyl)pyrazole-4-carboxylic acids. Scavenger resins were used to facilitate formation and purification of up to 27 amides from each of these acids in the last step. In addition, the Curtius reaction was applied to 12 of the acids followed by quenching with alcohols to afford a 108-member carbamate library. Certain compounds in the two libraries were toxic to C. elegans.     

4-Functionally Substituted 3-heterylpyrazoles: XII. 4-Chlorothieno[2,3-c]pyrazole-5-carbonyl Chlorides

3-(4-Pyrazolyl)acrylic acids reacted with excess thionyl chloride in the presence of benzyltriethylammonium chloride affording 4-chlorothieno[2,3-c]pyrazole-5-carbonyl chlorides which were converted into the corresponding acids, esters, and amides.     

Selective synthesis of functionalized pyrazoles from 5-amino-1H-pyrazole-4-carbaldehydes with sodium nitrite: 5-Amino-4-nitrosopyrazoles and pyrazole-4-carbaldehydes

A novel and efficient redox reaction was developed to react 5-amino-1H-pyrazole-4-carbaldehyde with sodium nitrite (NaNO₂) in an acidic solution (HCl/MeOH) to generate 5-amino-4-nitrosopyrazole, pyrazole-4-carbaldehyde, or diazenylpyrazole selectively. The results showed that 5-amino-4-nitrosopyrazoles were formed as the major product in the diluted acidic solution (≤2 N HCl in MeOH solution) through redox, formylation, and nitrosation reactions of NaNO₂. Intriguingly, pyrazole-4-carbaldehyde was the main product under 6 N HCl in MeOH solution.     

4-Functionally Substituted 3-Heterylpyrazoles: III. 3-Aryl(heteryl)pyrazole-4-carboxylic Acids and Their Derivatives

3-Aryl(heteryl)-4-formylpyrazoles were cleanly oxidized by potassium permanganate in water-pyridine medium to afford in high yield 3-aryl(heteryl)pyrazole-4-carboxylic acids, that were further converted into the corresponding chlorides and amides.     

Huisgen reaction of nitrile oxides and nitrile imines leading to isoxazoline and pyrazole-4,6-diones

Huisgen reaction of nitrile oxides and nitrile imines generated in situ in the presence of N-benzylmaleimide afforded regiospecifically the corresponding cis-3-aryl-5-benzyl-3a,4,6,6atetrahydro-4H, 6H-pyrrolo[3,4-d]isoxazoline-4,6-diones and cis-3-aryl-5-benzyl-1-(2′,4′-dibromophenyl)-3a, 4,6,6a-tetrahydro-1H,5H-pyrrolo[3,4-c]pyrazole-4,6-diones in good yield. Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 935–939, June, 2006.     

Synthesis and structure of dimethyl 3-(2-furoyl)pyrazole-4,5-dicarboxylate

1,3-Dipolar cycloaddition to the diazomethine grouping takes place in the reaction of 2-diazoacetylfuran with dimethyl acetylenedicarboxylate. The structure of the crystalline reaction product, viz., dimethyl 3-(2-furoyl)pyrazole-4,5-dicarboxylate, was investigated by x-ray diffraction analysis. The entire molecule, except for one of the two CO₂CH₃ groups, forms a planar conjugated system. The spectral characteristics of the synthesized compounds are presented.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 91–94, January, 1982.     

Terbium and dysprosium complexes with pyrazole-5-carboxylic acids. A relation of the luminescent properties to the characteristics of the ligands

The luminescent characteristics of Tb(III) and Dy(III) complexes with a number of 3R-substituted pyrazole-5-carboxylic acids were determined. Semiempirical (PM3) quantum-chemical calculations revealed a correlation between the luminescence intensities of the Tb(III) and Dy(III) complexes and (a) the ligand polarizability and (b) the electron density at the substituent atoms in position 3 of the pyrazole ring.     

A novel four-component synthesis of ethyl 6-amino-4-aryl-5-cyano-2,4-dihydropyrano[2,3-c]pyrazole-3-carboxylates

Ethyl 6-amino-4-aryl-5-cyano-2,4-dihydropyrano[2,3-с]pyrazole-3-carboxylates were synthesized via a four-component reaction of the sodium salt of diethyloxaloacetate, an aromatic aldehyde, hydrazine hydrate, and malononitrile. The products were obtained in moderate to high yields.     

Synthesis and biological activity of some new pyrazoline and pyrrolo[3,4-c]pyrazole-4,6-dione derivatives: reaction of nitrilimines with some dipolarophiles

Several 1,3-diaryl-5-(cyano-, aminocarbonyl- and ethoxycarbonyl-)-2-pyrazoline, pyrrolo[3,4-c]pyrazole-4,6-dione and 1,3,4,5-tetraaryl-2-pyrazoline derivatives were prepared by the reaction of nitrilimine with different dipolarophilic reagents. The new compounds were characterized using IR, (1)H-NMR, (13)C-NMR and mass spectra. Biological screening of some compounds is reported.     

A facile synthesis of 6-amino-2H, 4H-pyrano[2,3-F]pyrazole-5-carbonitriles in deep eutectic solvent

A convenient synthesis of 6-amino-2H,4H-pyrano[2,3-F]pyrazole-5-carbonitriles has been accomplished by one pot four-component cyclocondensation of aromatic aldehydes(1a-o) malanonitrile(2), ethyl acetoacetate(3), and hydrazine hydrate(4) in freshly prepared deep eutectic solvent, DES(choline chloride:urea). This protocol has afforded corresponding pyrano[2,3-F]pyrazoles in shorter reaction time with high yields, and it avoids the use of typical toxic catalysts and solvents.     

Research in the azole series. 103. Synthesis and 13C NMR study of pyrazole-4-carboxaldehydes

Ten new pyrazoles have been prepared and their ¹³C nmr chemical shifts compared with those of twelve other pyrazoles, some of them prepared purposely for this study. The chemical shifts are discussed statistically assuming that they are additive. A formyl group in the position 4 of the pyrazole ring produces a large effect on carbon C₄ (SCS = 17.3 ppm) and medium effects on carbons C₃ (SCS = 1.9 ppm) and C₅ (SCS = 3.8 ppm). The azines derived from pyrazole-4-carboxaldehydes are of the E,E-configuration.     

Synthesis of halosulfuron-methyl via selective chlorination at 3- and/or 5-position of pyrazole-4-carboxylates

Reactions of methyl pyrazole-4-carboxylates 4b-d with N-chlorosuccinimide under heating conditions without a solvent gave methyl 3,5-dichloro-1-methylpyrazole-4-carboxylate 4a in good yields. The reaction of 4a with sodium hydrosulfide led to a nucleophilic substitution on the 5-position regioselectively to afford methyl 3-chloro-1-methyl-5-mercaptopyrazole-4-carboxylate 6a, which was followed by oxidative chlorination and amination to obtain 3-chloro-1-methyl-5-sulfamoylpyrazole-4-carboxylate 2a. Finally, the reaction of 2a with phenyl 4,6-dimethoxypyrimidin-2-yl carbamate 7 provided methyl 3-chloro-5-(4,6-dimethoxypyrimidin-2-ylcarbamoylsulfamoyl)-1-methylpyrazole-4-carboxylate (halosulfuron-methyl) 1a promising herbicide in com.     

A novel synthetic approach towards pyrazole-4-carboxamides using N-(3-(dimethylamino)-2-formylacryloyl)formamide

Abstract  

A novel synthesis of pyrazole-4-carboxamides is reported. The reaction of N-(3-(dimethylamino)-2-formylacryloyl)formamide, an intermediate obtained by Vilsmeier–Haack formylation of acetonitrile, with hydrazine hydrate or monosubstituted hydrazines provides such compounds in good yields. This method has advantages over other methods for construction of such ring systems previously described in the literature.     

Mild,four-component synthesis of 6-amino-4-aryl-3-methyl-1,4-dihydropyrano[2,3-c]pyrazole-5-carbonitriles catalyzed by titanium dioxide nano-sized particles

A convenient and efficient solvent-free procedure is described for preparation of 6-amino-4-aryl-3-methyl-1,4-dihydropyrano[2,3-c]pyrazole-5-carbonitriles by four-component reaction of hydrazine hydrate, ethyl acetoacetate, aryl aldehyde, and malononitrile in the presence of a catalytic amount of titanium dioxide nano-sized particles. Short reaction times, high yields under ambient conditions, simple reaction, clean work-up, and reusability of the nano heterogeneous catalyst are the advantages of this method.     

Electrosynthesis of pyrazole-4-carboxylic acids by oxidation of 4-formylpyrazoles on NiO(OH)-electrode in aqueous alkaline solution

Electrochemical oxidation of di- and trisubstituted 4-formylpyrazoles on a Ni-anode in aqueous alkali led to the formation of the corresponding pyrazole-4-carboxylic acid in 60–90% yields. The yields of the target products depend on position of substituent in the pyrazole ring and are decreased in the following sequence of substituent at position 1 Me > Et > Ph, as well as when the aqueous medium was replaced with aqueous alcohol (50% Bu^tOH). Oxidation of 4-formylpyrazoles containing Me groups at the carbon atoms of the pyrazole ring led, to monoacids and also pyrazoledicarboxylic acids in small (1.5–14%) amounts; the latter were the oxidation products of the aldehyde and the Me groups.