Intramolecular cyclization of steroidal semicarbazones to pyrazoles using Vilsmeier reagent

The preparation of hitherto unknown steroidal heterocycles containing pyrazole fused to 6,7-position of the steroidal nucleus is described. These heterocycles were prepared by the action of Vilsmeier reagent with steroidal semicarbazones in DMF. The structure of the compounds has been established on the basis of their elemental analysis and spectral data. A general mechanistic scheme for these reactions is also suggested based on current and previous results.

A Mini-Review 5-Amino-N-Substituted Pyrazoles as Building Blocks for Bioactive Molecules

In this review a five-membered heterocyclic ring having two adjacent nitrogen atoms known as Pyrazole, we have framed 5-amino-N-substituted pyrazoles in particular focusing on its substantial role as a building block and starting materials for producing enormous heterocyclic skeletons. The existence of this moiety in larger compounds renders them to expose medicinal, pharmacological and biological therapeutic activities. Enormous drugs contain 5-amino-N-substituted pyrazoles such as celecoxib anti-inflammatory, antipsychotic, anti-obesity, analgesic, and antidepressant. We reported various routes of synthesis and the use of these compounds.

A Convenient Synthesis of Pyrazolylpyrazoles Using α-Oxo Ketene S,S- and N,S-Acetals

Substituted pyrazolylpyrazoles were synthesized through the reaction of hydrazine hydrate and α-oxo-(3, 5-dimethyl-1 H-pyrazole-1-ly)ketene S, S- and N,S-Acetals which were obtained from α-oxo-(3,5-dimethyl-1 H-pyrazole-1-yl) acetophenone. Pyrazolylpyrazole was also prepared via α-oxo ketene N,O-acetal by way of ring chain transformation.

Enantioselective synthesis of functionalized fluorinated dihydropyrano[2,3-c]pyrazoles catalyzed by a simple bifunctional diaminocyclohexane-thiourea

Enantioselective synthesis of functionalized fluorinated dihydropyrano[2,3-c]pyrazoles has been achieved via a diaminocyclohexane-thiourea catalyzed cascade Michael addition and Thorpe-Ziegler type cyclization in high yields （up to 98%） with moderate to good enantioselectivity （up to 90% ee）.

Palladium-catalyzed late-stage mono-aroylation of the fully substituted pyrazoles via aromatic C-H bond activation

The palladium-catalyzed late-stage aroylation of 4-methyl-1,5-diaryl-lH-pyrazole-3-carboxylates has been developed via direct and exclusive mono-Csp^2-H bond activation with broad substrate scope and good functional group tolerance. A dual-core dimeric palladacycle is confirmed by X-ray single crystal crystallography, and probably serves as an active species in the catalytic cycle.

Silica chloride catalyzed one-pot synthesis of fully substituted pyrazoles

Silica chloride catalysted one pot cyclocondensation of aldehydes,ethyl acetoacetate and phenyl hydrazine leading to substituted pyrazoles has been reported.

Two Dawson-type U(Ⅵ)-containing selenotungstates with sandwich structure and its high-efficiency catalysis for pyrazoles

Two novel uranium-containing selenotungstates Na_(3)[H_(19)(UO_(2))_(2)(μ_(2)-O)(Se_(2)W_(14)O_(52))_(2)]·41 H_(2)O(U_(2))and(NH_(4))_(10)[H_(4)(SeO)_(2)(UO_(2))_(2)(H_(2)O)_(2)(H_(2)Se_(2)W_(14)O_(52))(Se_(2)W_(14)O_(52))]·66 H_(2)O(Se_(2)U_(2))based on the{Se_(2)W_(14)O_(52)}unit were successfully prepared and fully characterized.To our knowledge,the uranium is firstly introduced into the selenotungstates.Moreover,it is notable that U_(2)exhibits excellent Lewis acid-base catalytic activities in the condensation cyclization of sulfonyl hydrazides with diketones to synthesize polysubstituted pyrazoles.All the desired products were obtained in moderate to good yields(up to 99%).

Base-mediated formal [3＋2] cycloaddition of β,γ-alkenyl esters and p-TsN3 for the synthesis of pyrazoles

A novel 1,8-diazabicyclo[5.4.0]undec-7-ene(DBU)-mediated formal cycloaddition of β,γ-alkenyl esters with p-tolylsulfonylazide(p-TsN_3) for the synthesis of 3,5-disubstituted pyrazoles has been developed.The reaction proceeded through diazotization of β,γ-alkenyl esters sequential with thermodynamic cyclization.p-Tolylsulfonylazide played a role as a source of two-nitrogen synthons.The reaction employs readily available starting materials,tolerates a wide range of functional groups,and proceeds under mild conditions.

Self-assembly of a new 3D platelike ternary-oxo-cluster:An efficient catalyst for the synthesis of pyrazoles

A new metal-oxo-clusters-based inorganic framework[NaCo_(2)Mo_(2)O_(7)(OH)_(3)]_(n)(NaCoMo),named as 3D platelike ternary-oxo-cluster,has been hydrothermally synthesized and characterized by single-crystal X-ray diffraction structure analysis,FT-IR spectroscopy,powder X-ray diffraction(PXRD),scanning electron microscope(SEM),energy-dispersive X-ray spectroscopy(EDS)analyses,X-ray photoelectron spectroscopy(XPS)and thermogravimetric analysis(TGA).Structure analysis reveals that there are no classical building units in NaCoMo,and the asymmetric units of NaCoMo are directly extended into a new platelike 3D structure.Density functional theory calculations(DFT)indicates that the crystal formation process is exothermic and the structure is extremely stable.In addition,the compound presents excellent catalytic activity in the condensation and cyclization reaction of sulfonyl hydrazides and 1,3-diketones to synthesize pyrazoles,and the yield of the desired product is up to 99%.The successful synthesis of NaCoMo represents the discovery of a new kind of non-classical polyoxometalates.

Morpholine triflate promoted one-pot,four-component synthesis of dihydropyrano[2,3-c]pyrazoles

A one-pot, four-component reaction of ethyl acetoacetate, hydrazine hydrate, aldehydes, and malononitrile was discussed using Lewis acid catalyst morpholine triflate （MorT） to afford a series of dihydropyrano[2,3-c]pyrazoles, which were generally catalyzed by organic alkalis. Moderate to excellent yields, no chromatographic purification, and evasion of environmentally hazardous solvents in the reaction process make this protocol very useful for academia and industry.

Efficient synthesis of fused pyrazoles via simple cyclization of o-alkynylchalcones with hydrazine

The synthesis of pyrazole derivatives from o-alkynylchalcones and hydrazine via simple cyclization is described. This greener synthetic methodology provides a straightforward approach to the synthesis of a variety of pyrazole derivatives under mild reaction condition.

STRUCTURAL DETERMINATION AND ^(13)C NMR STUDIES OF ALKYL IMIDAZOLES AND PYRAZOLES

INTRODUCTION Due to their special structures, two nitrogen five-membered heterocyclic com- pounds, including imidazole and pyrazole derivatives, are very important in biochem- istry, medical chemistry, physical chemistry, organic chemistry and catalysis. How- ever, unbranched alkyl-substituted imidazoles and pyrazoles are relatively few.

Au（I）-Catalyzted Synthesis of 5-Bromodifluoromethyl Pyrazoles from Fluorinated Alkynyl Ketones and Hydrazine

Fluorinated alkynyl ketones react with hydrazine to give fluorinated pyrazols in good to excellent yields with Au（I） as catalyst. All the reactions were carried out at room temperature with excellent regioselectivity.

Effects of Micelle on Pyrazoles as Antioxidants in Radical-induced Oxidation of DNA

Effects of 4-（1,3-diphenyl-1H-pyrazol-5-yl）phenol（APP）,4-（1,5-diphenyl-lH-pyrazol-3-yl）phenol（BPP） and 4-（3,5-diphenyl-1H-pyrazol-1-yl）phenol（CPP） on 2,2＇-azobis-（2-amidinopropane hydrochloride）（AAPH）-induced oxidation of DNA were measured in the presence of various concentrations of Triton X-100,cetyltrimethylammonium bromide（CTAB）,or sodium dodecyl sulfate（SDS） in order to clarify the influence of neutral,cationic and anionic microenvironments on antioxidant capacities of APP,BPP and CPP.Although these surfactants can protect DNA against AAPH-induced oxidation,the pyrazoles in the presence of these surfactants functioned as prooxidants when the concentrations of Triton X-100 and CTAB increased.However,CPP exhibited antioxidant property with the increase of the concentration of CTAB.On the contrary,APP,BPP and CPP were antioxidants in the presence of various concentrations of SDS.The added surfactants resulted in the complication of the microenvironments around DNA,pyrazoles and peroxyl radical（ROO＊） derived from AAPH.The anionic charge of SDS was beneficial to enhancing the antioxidant effectiveness of these pyrazoles.It can be concluded that the charge property of surfactants markedly influenced the behavior of an antioxidant in AAPH-induced oxidation of DNA.

Soluble Polymer-Supported Synthesis of Pyrazoles via 1,3-Dipolar Cycloaddition Strategy

Rapid parallel liquid-phase synthesis of pyrazoles has first been developed. The 1,3-dipolar cycloaddition be-tween nitrilimines generated in situ and soluble polymer-supported alkynyl or alkenyl dipolarophiles in parallel one-pot fashion gave the corresponding PEG-supported regioisomeric pyrazoles or regiospecific pyrazolines. The latter was assuredly oxidated by DDQ to PEG-supported regiospecific pyrazoles. Cleavage from the support under mild conditions afforded pyrazoles in good yields and high purity.

Synthesis of 1,3,5-Trisubstituted [4-tert-Butyl 2-（5,5-difluoro- 2,2-dimethyl-6-vinyl-l,3-dioxan-4-yl）acetate]pyrazoles via a Pd-Catalyzed C--H Activation

The gem-difluoromethylenated acetonide 2 was efficiently synthesized as new precursor of HMG-CoA reduc- tase inhibitor. Straightforward olefination via Pd-catalyzed C4-H activation of 1,3,5-trisubstituted pyrazoles 1 was proceeded smoothly in the presence of Pd（OAc）2 and AgCO3. This protocol has merits in terms of the improved atomic economy and prevention from the generation of by-products.

Heterocyclic Synthesis via Enaminones: Synthesis and Molecular Docking Studies of Some Novel Heterocyclic Compounds Containing Sulfonamide Moiety

4-Acetyl-N, N-diethylbenzenesulfonamide (1) was condensed with dimethylformamide dimethy-lacetal (DMF-DMA) to yield the enaminone, which reacts readily with different reagents to give the corresponding pyrazoles, triazolopyrimidine, imidazopyridine, pyrimidopyrimidine, pyrazolopyrimidine, benzofuran, pyranone, pyridine, pyrimidine and pyrazolopyridazine derivatives. These compounds were designed to comply with the general features of sulfonamide pharmacophore which act as Cyclooxygenase (COX-2) inhibitors. Virtual screening using molecular docking studies of the synthesized compounds was performed by (MOE), the molecular docking results indicate that, some synthesized compounds suitable inhibitor against (COX-2) with further modification.

Synthesis and <i>in Vitro</i>Cytotoxic Activity of Novel Pyrazole-3,4-dicarboxylates

N-Aryl-C-ethoxycarbonylnitrile imines (3a-g) react with ethyl cyanoacetate 1 in 1,3-dipolar cycloaddition to yield novel pyrazole-3,4-dicarboxylates (4a-g) in moderate yields. The reaction of pyrazole-3,4-dicarboxylates (4a, d) with hydrazine afforded pyrazolo[4,3-d]pyridazine-4,7-diones (5a, d) in good yields. All compounds were fully characterized by spectroscopic methods. Some of the newly synthesized compounds were evaluated for their cytotoxic activity against murine P815 mastocytoma cell line.

Use of Solid-Supported Reagents towards Synthesis of 2-Arylbenzoxazole, 3, 5-Diarylisoxazole and 1, 3, 5-Triarylpyrazole

Herein we report a convenient and efficient synthesis of 2-Arylbenzoxazole from the Schiff’s bases of 2-Aminophenol, 3, 5-Diarylisoxazole from α, β-unsaturated ketoxime and 1,3,5-Triarylpyrazole from 2-pyrazoline and N-Arylhydrazone by using milder, less toxic and less expensive-NBS-SiO2, KMnO4-Al2O3, PCC-SiO2 and ACC-Al2O3 as solid-supported oxidizing agents at room temperature. Within the framework of Green Chemistry, the use of solid supported reagents has many advantages such as 1) they are easy to remove from reactions by filtration 2) excess reagents can be used to drive the reaction without introducing any difficulties in purification 3) such solid-supported reagents react differently, mostly more selectively, than their unbound counterparts and 4) toxic, noxious and explosive chemicals are handled more safely when contained on solid support.

Cyclization Reaction of α-Triazolyl-α, β-unsaturated Ketones with Phenyl hydrazine

The reaction of α-triazolyl-α, β-unsaturated ketones with phenyl hydrazine was studied. The result indicated that cyclization took place and new heterocyclic compounds of substituted 4,5-2H-pyrazoles were obtained, whose structures and conformation were characterized by 1H NMR, IR, MS, elemental analysis and X-ray diffraction.