- An Intramolecular Wittig Approach toward Heteroarenes: Synthesis of Pyrazoles, Isoxazoles, and Chromenone-oximes
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α-Halohydrazones/ketoximes are transformed into trisubstituted pyrazoles/disubstituted isoxazoles by treatment with phosphine, acyl chloride, and a base. Mechanistic investigations revealed the in situ formation of azo/nitroso olefin intermediates which underwent a tandem phospha-Michael/N- or O-acylation/intramolecular Wittig reaction to afford the heteroarenes in moderate to good yields. Further, proper functionalization of α-haloketoximes and a change of conditions allowed the chemoselective synthesis of chromenone-oximes as well as rearranged isoxazoles, thereby realizing a diversity-oriented synthesis.
- Khairnar, Pankaj V.,Lung, Tsai-Hui,Lin, Yi-Jung,Wu, Chi-Yi,Koppolu, Srinivasa Rao,Edukondalu, Athukuri,Karanam, Praneeth,Lin, Wenwei
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p. 4219 - 4223
(2019/06/17)
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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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- 5-Hydroxy-2-pyrazolines and some of their 1-substituted analogs
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The use of 1,3-dicarbonyl compounds containing strong electron-withdrawing substituents (perfluoroalkyl, 4-nitrophenyl) at one of the carbonyl groups in reaction with hydrazine or its monosubstituted derivatives (4-nitro- and 2,4-dinitrophenylhydrazines) leads to the formation of stable intermediates for the synthesis of pyrazoles (5-hydroxy-2-pyrazolines) or their linear tautomers (hydrazones).
- Zelenin,Tugusheva,Yakimovich,Alekseev,Zerova
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p. 668 - 676
(2007/10/03)
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- Study of the reactivity of α-acylenaminoketones. Synthesis of pyrazoles
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The reactions of 4-(methylamino)-3-penten-2-one with diazoketones yielded the α-acylenaminoketones 1-3 in good yields. Preparation of the α-acylenaminoketone 4 was carried out by treatment of 4-(t-butylamino)-3-penten-2-one with benzoyl chloride being followed by reaction of transamination with methylamine. The reactions were carried out in five different solvents and were submitted to gas chromatography/mass spectrometry analysis, with the goal of obtaining substituted pyrazoles and determining which of the carbonyls would preferentially be attacked by the nucleophile. The reactions of compounds 1-4 with hydrazine reagents led to the formation of the pyrazoles 5-7a-q. Small amounts of 4-methylamino-2-pentenones 10a-q, amides 11a-q and pyrazoles 12a-q were also obtained in these reactions. The unexpected formation of pyrazoles 15d,h,q was detected when methanol and N,N-dimethylformamide were used as solvents in the reactions of α-acylenaminoketone 4 with hydrazine reagents.
- Negri,Kascheres
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p. 109 - 123
(2007/10/03)
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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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- Cross-coupling of 1-aryl-5-bromopyrazoles: Regioselective synthesis of 3,5-disubstituted 1-arylpyrazoles
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The cross-coupling of 1-aryl-5-bromopyrazoles 4 with alkynes, vinyltins and arylboronic acids promoted by Pd(PPh3)4 afforded unsymmetrical 3,5- disubstituted 1-arylpyrazoles 5-8 in excellent yields, 1-Aryl-5- bromopyrazoles 4 were prepared from their corresponding 1-arylpyrazolones 3 with PBr3 in refluxing acetonitrile. (C) 2000 Elsevier Science Ltd.
- Wang, Xiao-Jun,Tan, Jonathan,Grozinger, Karl
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p. 4713 - 4716
(2007/10/03)
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- 5-Hydroxy-4,5-Dihydropyrazoles
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The use of β-diketones with strong electron-withdrawing substituents in reaction with hydrazine and its monosubstituted derivatives leads to the stable intermediates of pyrazole synthesis - 5-hydroxy-4,5-dihydropyrazoles or their open chain isomers.
- Zelenin, Kirill N.,Alekseyev, Valery V.,Tygysheva, Alja R.,Yakimovitch, Stanislav I.
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p. 11251 - 11256
(2007/10/02)
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- Oxidative Cyclization of Arylhydrazones of Chalcones and Benzalacetones to Pyrazoles by Thianthrene Cation Radical
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Phenyl-, (p-nitrophenyl)-, and (2,4-dinitrophenyl)hydrazones of chalcone (benzalacetophenone), benzalacetone, and of some of their derivatives undergo oxidative cyclization in reactions with thianthrene cation radical perchlorate.The products are, respect
- Kovelesky, Albert C.,Shine, Henry J.
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p. 1973 - 1979
(2007/10/02)
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