- Pyrrole and Pyrazole Ring Closure in Heterogeneous Media
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Pyrroles and pyrazoles may be conveniently prepared by dispersing primary amines or hydrazines and 1,4- or 1,3-diketones, respectively, on alumina or clay (montmorillonite K 10) without solvent, keeping the mixture at 20 deg C or higher temperatures for 1-26 h, and then eluting the product with dichloromethane.
- Texier-Boullet, F.,Klein, B.,Hamelin, J.
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- Palladium-catalyzed coupling of pyrazole triflates with arylboronic acids
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A general protocol for the palladium-mediated Suzuki coupling reaction of pyrazole inflates and aryl boronic acids has been developed. The use of additional dppf ligand was determined to increase product yields allowing for the use of a broad range of rea
- Dvorak, Curt A.,Rudolph, Dale A.,Ma, Sandy,Carruthers, Nicholas I.
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- Reactivity of p-phenyl substituted β-enamino compounds using K- 10/ultrasound. I. Synthesis of pyrazoles and pyrazolinones
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The reactivity of the β-enamino ketones, 3-amino-1-(p-phenyl- substituted)-2-buten-1-ones 1a-d and β-enamino esters, ethyl 3-amino-3-(p- phenyl-substituted)-2-propenoates 5a-d was systematically studied when allowed to react with hydrazine and methylhydrazine under solid support K- 10/ultrasound conditions and in homogeneous media (reflux in ethanol or dichloromethane). The products were pyrazoles 2a-d, N-methylpyrazoles 3a-d, 4a-d and N-methylpyrazolinones 6a-c and 7a-c. The regiochemistry of the cyclization reactions showed dependence upon the reaction conditions employed as well as upon the substituent in the aromatic ring.
- Valduga,Braibante,Braibante
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- Small molecule library synthesis using segmented flow
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Flow chemistry has gained considerable recognition as a simple, efficient, and safe technology for the synthesis of many types of organic and inorganic molecules ranging in scope from large complex natural products to silicon nanoparticles. In this paper
- Thompson, Christina M.,Poole, Jennifer L.,Cross, Jeffrey L.,Akritopoulou-Zanze, Irini,Djuric, Stevan W.
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experimental part
p. 9161 - 9177
(2012/01/03)
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- A novel synthesis of fluorinated pyrazoles via gold(I)-catalyzed tandem aminofluorination of alkynes in the presence of Selectfluor
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A mild and efficient protocol for the synthesis of fluorinated pyrazoles has been developed via gold(I)-catalyzed tandem aminofluorination of alkynes in the presence of Selectfluor. This method offers a broad substrate scope.
- Qian, Jianqiang,Liu, Yunkui,Zhu, Jie,Jiang, Bo,Xu, Zhenyuan
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supporting information; experimental part
p. 4220 - 4223
(2011/10/04)
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- Regioselective synthesis of 1,3,5- and 1,3,4,5-substituted pyrazoles via acylation of N-Boc-N-substituted hydrazones
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Acylation of N-Boc-N-methylhydrazones followed by TFA treatment affords regioselective access to substituted pyrazoles. Both regioisomers of 1-methyl-3,5-disubstituted-1H-pyrazoles can be selectively obtained. This procedure can also be employed for the r
- Tinarelli, Alessandro,Righi, Paolo,Rosini, Goffredo,Andreotti, Daniele,Profeta, Roberto,Spada, Simone
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experimental part
p. 612 - 617
(2011/03/19)
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- The preparation of substituted pyrazoles from β,β-dibromo-enones by a tandem condensation/Suzuki-Miyaura cross-coupling process
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Two consecutive tandem processes are described for the regioselective, two-step synthesis of 1,3,5-trisubstituted pyrazoles from α- hydroxyketones. The first, a tandem MnO2-mediated oxidation/Ramirez olefination reaction, provides a facile route to β,β-dibromo-enones. These valuable 1,3-dicarbonyl synthons can then be converted into 1,3,5-trisubstituted pyrazoles via a second tandem hydrazine condensation/Suzuki-Miyaura cross-coupling reaction. Using these procedures, a range of aryl and alkyl α-hydroxyketones have been transformed regioselectively into 1,3,5-trisubstituted pyrazoles. Georg Thieme Verlag Stuttgart.
- Beltrán-Rodil, Sandra,Edwards, Michael G.,Pugh, David S.,Reid, Mark,Taylor, Richard J.K.
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scheme or table
p. 602 - 606
(2010/09/18)
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- Reactions of lithium silylcuprates with pyrazolium and indazolium salts
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Although pyrazolium salts have been shown to be unreactive toward lithium carbocuprates, these substrates were opened by lithium silylcuprate reagents to give versatile N-silylated β-enaminoimines stabilized by coordination of the silyl group with both ni
- Gonzalez-Nogal, Ana M.,Calle, Mariola,Cuadrado, Purificacion
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p. 6089 - 6096
(2008/09/17)
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- A new and a convenient route to enaminones and pyrazoles
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A new method has been developed for the regioselective preparation of enaminones and pyrazoles from 1,3-diketonatoboron difluorides. The reactions proceed smoothly under mild reaction conditions, producing enaminones and pyrazoles in high yields.
- Stefane, Bogdan,Polanc, Slovenko
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- Scope and limitations in the regioselective synthesis of 1,3,5-trisubstituted pyrazoles from β-amino enones and hydrazine derivatives. 13C-chemical shift prediction rules for 1,3,5-trisubstituted pyrazoles
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β-amino enones react with hydrazine derivatives to give regioselectively 1,3,5-trisubstituted pyrazoles. The synthetic method only presents limitations when the β-substituent of the enone and the hydrazine substituent are bulky or possess an electron withdrawing character. Comparison of the 13C-NMR spectra of the seventy pyrazoles allowed us to estimate a 13C-chemical shift prediction rule for 1,3,5-trisubstituted pyrazoles, with deviations of less than ± 1 ppm.
- Alberola, Angel,Calvo Bleye, Luis,Gonza?lez-Ortega, Alfonso,Sa?daba, M.Luisa,San?udo, M.Carme
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p. 331 - 352
(2007/10/03)
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- Reactivity of p-Phenyl Substituted β-Enamino Compounds using K-10/ultrasound. I. Synthesis of Pyrazoles and Pyrazolinones
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The reactivity of the β-enamino ketones, 3-amino-l-(p-phenyl-substituted)-2-buten-l-ones la-d and β-enamino esters. Ethyl-3-amino-3-(p-phenyl-substituted)-2-propenoates 5a-d were evaluated by systematic studies of the reactions with hydrazine and methylhydrazine by reactions with solid support K-10/ultrasound and homogeneous media (reflux in ethanol or dichloromethane) yielding pyrazole rings 2a-d, Af-methylpyrazoles 3a-d, 4a-d and N-methylpyrazolinones 6a-c and 7a-c. The regiochemistry of the cyclization showed dependence of the reaction conditions employed as well as the substituent in the aromatic ring.
- Valduga, Claudete J.,Braibante, Hugo S.,Braibante, Mara E.F.
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p. 189 - 192
(2007/10/03)
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- INVESTIGATIO OF THE MECHANISMS OF FORMATION OF HETEROCYCLES BY NMR SPECTROSCOPY. INTERMEDIATES IN THE PRODUCTION OF PYRAZOLES FROM 1,3-DIKETONES AND HYDRAZINES
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The structure of the intermediates formed in the reaction of 1,3-diketones RCOCH2COCH3 (R = Me, Et, t-Bu, Ph, CF3) with hydrazines NH2NHR' (R'= H, Me) in methanol and chloroform was determined by NMR spectroscopy in the normal and flow techniques.When R' = H, the reaction takes place through the formation of dihydroxypyrazolidine and 5-hydroxy-2-pyrazolines; for R'= Me, in addition, intermediate products with ketohydroxyazine and ketoenehydrazone structures were detected.A scheme with their participation is proposed for the formation of the isomeric pyrazoles.A pre-equilibrium between the 1,3-diketone, its hydrazinium salt in the Z,Z configuration, and the anion in the E,Z configuration was detected.The reaction rate of the ketone form of the 1,3-diketone is significantly higher than the reaction rate of the enol.
- Selivanov, S. I.,Bogatkin, R. A.,Ershov, B. A.
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p. 788 - 795
(2007/10/02)
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- Recherches en serie triazepine XVI. Condensation des composes β-dicarbonyles avec les thiosemicarbazides
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Condensations of β-dicarbonyl compounds with thiosemicarbazide and 1- and 2-methylthiosemicarbazide give three types of heterocyclic compounds.Depending upon the reagents and experimental conditions, triazepinones, triazepines, 1,2,4-triazolines or pyrazoles are formed.Mechanisms explaining these cyclisations are proposed.
- Hasnaoui, A.,Lavergne, J.-P.,Viallefont, Ph.
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p. 301 - 306
(2007/10/02)
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- Reaction of pyrylium salts with hydrazine and methylhydrazine. Concerning the scope of the 1,2(4H)-diazepine synthesis
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The reaction of pyrylium salts 1a-e with methylhydrazine gives pyrazolines(2), pyrazoles(3), pyridines(4), 1,2-diazepine(5), and N-methylaminopyridinium salts(6).Product composition has been studied as a function of pyrylium salt counter anion, concentration of methylhydrazine, and conditions of the reaction(Table 1).Pyridines(4), and 1,2-diazepines(5) are minor components, the major products being the pyrazolines(2) and pyrazoles(3).The reactions of more unusual pyrylium salts(1f-i, 8a, 9a, 9c, and 11a) with hydrazine have been shown to provide 1,2(4H)-diazepines(10, 12-15) and N-aminopyridinium salts(8b, 9b) (Table 2), the nature of the product apparently depending on the absence or presence of 2-methyl substitution respectively in the starting pyrylium salts.
- Harris, D. J.,Kan, G. Y.-P.,Tschamber, T.,Snieckus, V.
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p. 494 - 500
(2007/10/02)
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