Synthesis of 5-substituted 1-aryl-1H-pyrazole-4-acetonitriles, 4-methyl-1-phenyl-1H-pyrazole-3-carbonitriles and pharmacologically active 1-aryl-1H-pyrazole-4-acetic acids

Lithium aluminum hydride reduction of 5-substituted or unsubstituted ethyl or methyl 1-aryl-1H-pyrazole-4-carboxylates gave, generally in excellent yields, 5-substituted or unsubstituted 1-aryl-1H-pyrazole-4-methanols which afforded the corresponding 1-aryl-4-(bromomethyl)-1H-pyrazoles with hydrobromic acid in acetic acid solution. These crude intermediates gave by reaction with potassium cyanide in dimethylsulfoxide solution 1-aryl-1H-pyrazole-4-acetonitriles only in the case of 5-unsubstituted compounds, otherwise mixtures of 5-substituted 1-aryl-1H-pyrazole-4-acetonitriles and 4-methyl-1-phenyl-1H-pyrazole-3-carbonitriles were generally obtained. Acetonitriles IIIa,b,i,l gave in excellent yields the corresponding 1-aryl-1H-pyrazole-4-acetic acids Va,b,i,l by alkaline hydrolysis. Compounds Vb,i,l showed in the writhing test appreciable analgesic properties, associated with low acute toxicity; moreover, compound VI exhibited a statistically significant antiinflammatory activity in the carrageenan-induced edema assay.     

Synthesis of 3-aryl-5-dichloromethyl-1H-pyrazole-1-carboxamides from 1-aryl-3,4,4-trichlorobut-3-en-1-ones

The reaction of 1-aryl-3,4,4-trichlorobut-3-en-1-ones with semicarbazide hydrochloride in the presence of sodium acetate is accompanied by prototropic allylic rearrangement, leading to the formation of two isomeric products, semicarbazones of the initial ketones and 1-aryl-3,4,4-trichlorobut-2-en-1-one semicarbazones. The latter undergo heterocyclization in the presence of triethylamine to give the corresponding 3-aryl-5-dichloromethyl-1H-pyrazole-1-carboxamides.     

Synthetic and structural studies of some chloro-substituted methyl 2,1-benzisoxazole-3-carboxylates and related compounds

Methyl 5-chloro- and 5,7-dichloro-2,1-benzisoxazole-3-carboxylates have been synthesized by treatment of o-nitromandelic and 5-chloro-2-nitroamandelic methyl esters, respectively, with thionyl chloride under appropriate reaction conditions. The structural assignments of both heterocyclic products were based on elemental and spectral analyses, and their conversion to the corresponding 5-chloro- and 5,7-dichloro substituted 2,1-benzisoxazole-3-carboxylic acids and isatins. Methyl α-chloro-o-nitrophenylacetate and o-nitrophenylcarbomethoxymethinyl sulfite were also obtained from reactions of methyl o-nitromandelate and thionyl chloride. A possible reaction mechanism involving two consecutive nucleophilic substitutions of methyl o-nitromandelate with thionyl chloride was proposed to account for the formation of methyl 5-chloro-2,1-benzisoxazole-3-carboxylate.     

Synthesis and anti-TMV activity of novel N-(3-alkyl-1H-pyrazol-4-yl)-3-alkyl-4-substituted-1H-pyrazole-5-carboxamides

In order to investigate the biological activity of novel bis-pyrazole compounds,a series of N-（3-alkyl-5-（N-methylcarbamyl）- 1H-pyrazol-4-yl）-3-alkyl-4-substituted-1H-pyrazole-5-carboxamides were designed and synthesized with ethyl 3-alkyl-1H-pyrazole -5-carboxylate 1 as starting materials.N-Methyl-3-alkyl-4-amino-1H-pyrazole-5-carboxamides 6 were obtained from 1 via 5 steps.3-Alkyl-4-substitued-1H-pyrazole-5-carboxyl chlorides 4a,4b,11a,11b,11c or 12 were also obtained from 1 via several steps.Target compounds 7a-7g were obtained after the reaction of 6 with the above 1H-pyrazole-5-carboxyl chlorides.Preliminary bioassay showed some compounds possessing good inactivation effect against TMV（tobacco mosaic virus）.Compound 7a showed higher activity superior to ningnanmycin at a concentration of 5.0×10^-4 g/mL and equal activity at 1.0×10^-4 g/mL;7b and 7c showed equal activity to virazole both at concentrations of 5.0×10^-4 g/mL and 1.0×10^-4 g/mL.     

A new synthetic route to chiral 3-aryl-5-ethyl-1,4,2-oxazaphosphorines

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Structure of 1-aryl-3-alkyl-5-(2-benzothiazolyl)formazans

The isomeric and tautomeric structures of 1-aryl-3-alkyl-5-(2-benzothiazolyl)formazans in solutions were investigated by means of NMR, IR, and electronic spectroscopy. It is shown that the nature of the solvent and the alkyl substituent in the 3 position affects the ratio of the Z and E isomers relative to the C=N bond of the azohydrazone chain. An increase in the length of the alkyl substituent in the 3 position leads to preponderance of the Z isomer in solution, while branching stabilizes the Z configuration with an N²...HN⁵ intramolecular hydrogen bond (IMHB), regardless of the solvent. The nature of the solvent has a significant effect on the ratio of the amino and imino tautomeric forms of the E isomers. The benzothiazolylhydrazone form predominates in CHCl₃, while the tautomer with a benzothiazolidene fragment is the major form in DMSO.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 834–839, June, 1993.     

A regioselective route to 5-substituted pyrazole- and pyrazoline-3-phosphonic acids and esters

The regioselective synthesis of 5-substituted-3-dimethoxyphosphono-pyrazoles and -2-pyrazolines has been accomplished through the 1,3-dipolar cycloaddition of a suitable nitrile imine to monosubstituted alkynes and alkenes. Examples of hydrolysis of the heterocyclic phosphonic esters to the corresponding acids are described.     

Synthesis and properties of 5-aryl-3-diazo-3H-pyrazoles and 3-aryl-1H-pyrazole-5-diazonium salts. Preparation and cytolytic activity studies of 2-arylpyrazolo-[5,1-c][1,2,4]benzotriazines

Chemistry of Heterocyclic Compounds - A comparative analysis of physicochemical properties and reactivity of 3-aryl-1H-pyrazole-5-diazonium tetrafluoroborates and 5-aryl-3-diazo-3H-pyrazoles in azo...     

A one-pot three-component reaction to access 1-alkyl-2-aryl-5-nitrobenzimidazoles under solvent-free conditions

A novel and expeditious method to access 1-alkyl-2-aryl-5-nitrobenzimidazoles has been developed. Enlisting solvent-free conditions, 2-fluoro-5-nitroaniline, a primary amine, and substituted aldehyde were melted together in one-pot to generate a variety of 1-alkyl-2-aryl-5-nitrobenzimidazoles.     

A new synthesis of 1-aryl-5-cyano-1H-pyrazole-4-carboxylic acid,ethyl esters

A novel conversion of 5-amino-1-aryl-1H-pyrazole-4-carboxylic acid, ethyl esters to the corresponding 5-cyano esters is described. The process involves nonaqueous diazotization of the amine to form the methyl thioether, which is oxidized to the methyl sulfone, which, in turn, is displaced by cyanide ion. The cyano esters are precursors to chemical hybridizing agents in wheat and barley.     

A different route to 3-aryl-4-hydroxycoumarins

We herein report the simple and direct arylation of 4-hydroxycoumarins by photoinduced reaction with aryl halides (iodobenzene, iodonaphthalene, 4-iodoanisole, 2-iodoanisole). Good yields of 3,4-disubstituted coumarins were obtained in these reactions (>60%). Extension of the procedure to the reaction with o-dihalobenzenes leads to the synthesis of ring closure products which bear a tetracyclic aromatic-condensed ring system, although in lower overall yields (≈45%).     

Thermal isomerization of 5-methoxy-3-arylisoxazoles to methyl 3-aryl-2H-azirine-2-carboxylates

The thermal isomerization of 5-methoxy-3-arylisoxazoles to methyl 3-aryl-2H-azirine-2-carboxylates was subjected to a kinetic study. A correlation between the isomerization rate constants and the ⁺ constants of the substituents in the aromatic ring is observed. The enthalpies of formation of a number of isoxazoles and 2H-azirines were calculated. The effect of the nature of the substituents on the mutual isomerization of isoxazoles and azirines is discussed. The results make it possible to refute the approved and previously proposed diradical mechanism for the isomeric transformations and are in agreement with a nitrene mechanism for the formation of azirines.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1053–1056, August, 1978.     

A direct route to 2-alkyl-4-carbethoxy-5-vinyloxazoles

The reaction of an α-chloroglycinate ester with the dimethylaluminum acetylide derivative of phenyl propargyl ether provides the corresponding 5-vinyloxazole in 40-50% yield.     

Synthesis and Characterization of Novel Methyl (3)5-(N-Boc-piperidinyl)-1H-pyrazole-4-carboxylates

Series of methyl 3- and 5-(N-Boc-piperidinyl)-1H-pyrazole-4-carboxylates were developed and regioselectively synthesized as novel heterocyclic amino acids in their N-Boc protected ester form for achiral and chiral building blocks. In the first stage of the synthesis, piperidine-4-carboxylic and (R)- and (S)-piperidine-3-carboxylic acids were converted to the corresponding β-keto esters, which were then treated with N,N-dimethylformamide dimethyl acetal. The subsequent reaction of β-enamine diketones with various N-mono-substituted hydrazines afforded the target 5-(N-Boc-piperidinyl)-1H-pyrazole-4-carboxylates as major products, and tautomeric NH-pyrazoles prepared from hydrazine hydrate were further N-alkylated with alkyl halides to give 3-(N-Boc-piperidinyl)-1H-pyrazole-4-carboxylates. The structures of the novel heterocyclic compounds were confirmed by ¹H-, ¹³C-, and ¹⁵N-NMR spectroscopy and HRMS investigation.     

Novel Synthesis of 5-Amino-3-bromo-1-(tert-butyl)-1H-pyrazole-4-carbonitrile: A Versatile Intermediate for the Preparation of 5-Amino-3-aryl-1-(tert-butyl)-1H-pyrazole-4-carboxamides

A simple, novel, and efficient route for the synthesis of 5-amino-3-aryl-1-(tert-butyl)-1H-pyrazole-4-carboxamides 1 has been devised. Preparation of pyrazole bromide 3 from potassium tricyanomethanide can be accomplished in only two steps in good yield and features a selective Sandmeyer reaction on the corresponding diaminopyrazole. This allows for a more versatile synthesis of 5-amino-3-aryl-1-(tert-butyl)-1H-pyrazole-4-carboxamides 1 than was previously possible.     

1H and 13C NMR studies on 3-aryl-5-alkyl-2,4-oxazolidinediones. The magnetic non-equivalence of isomeric nuclei

Magnetic non-equivalence of diastereotopically related proton and ¹³C nuclei in enantiomeric and diastereomeric rotational isomers of 3-aryl-5-alkyl-2,4-oxazolidinedlones has been investigated. Steric interactions between the aryl and the heterocyclic moieties of these compounds produce sufficient restriction to rotation about the aryl C? N bond that the presence of torsional isomers may be detected at normal temperatures. Free energies of activation for rotation have been calculated. Chemical shift differences, associated with rotational isomerism, may be detected for both the proton and the ¹³C nuclei on the hetero ring, but only in the ¹³C spectra of the nuclei on the aryl moiety.     

A concise and regioselective synthesis of 1-alkyl-4-imidazolecarboxylates

Reaction between ethyl 3-N,N-(dimethylamino)-2-isocyanoacrylate (1) and a primary amine (2) regioselectively affords 1-alkyl-4-imidazolecarboxylates (3) in good yields (52-89%). The method is applicable to unhindered and hindered amine substrates, as well as those containing reactive functionality such as alcohols and secondary and tertiary amines. [reaction: see text]     

Synthesis of cucurbitine derivatives: facile straightforward approach to methyl 3-amino-4-aryl-1-methylpyrrolydine-3-carboxylates

A general three- or four-step synthesis of cis- and trans-substituted cucurbitine (3-aminopyrrolidine-3-carboxylic acid) derivatives from methyl 2-nitroacetate is reported. The first step utilizes a Knoevenagel condensation with five different aromatic imines or their corresponding aldehydes to form (Z/E)-mixtures of α-nitro acrylates. The second step gives rise to the pyrrolidine-core structures of the title compounds by a 1,3-dipolar cycloaddition reaction using an azomethine ylide. The last step consists of reduction of the nitro group to yield both diastereoisomers of the corresponding 4-aryl cucurbitine methyl esters.     

Synthesis of 1-aryl-5-(trifluoromethyl)-1H-pyrazole-4-carboxylic acids and esters

Ethyl 1-aryl-5-(trifluoromethyl)-1H-pyrazole-4-carboxylates 2 were prepared by the condensation of arylhydrazines with ethyl 3-ethoxy-2-(trifluoroacetyl)-2-propenoate (1a) at low temperature. The corresponding acids were also synthesized. X-ray diffraction analysis of an amide derivative 4 verified the position of the trifluoromethyl group on the pyrazole ring.