Novel method for the synthesis of 4-(azol-5-yl)isoxazoles

Бакулев, В. А.; Efimov, Ilya; Belyaev, N. A.; Zhidovinov, Sergey S.; Rozin, Yu. A.; Волкова, Н. Н.; Хабарова, А. А.; Eltsov, Oleg S.

doi:10.1007/s10593-013-1225-1

Cited by 14 publications

(6 citation statements)

References 6 publications

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“…The starting enamines 1a–e bearing imidazole ( 1a,b ) and isoxazole ( 1c–e ) rings were prepared from the corresponding 5-methylazoles by reaction with dimethylformamide dimethyl acetal (DMF-DMA) adapting synthetic procedures published earlier [26–30]. Their structures can be unambiguously assigned as the trans -isomers by observing the coupling constant ( J = 13.0–13.6 Hz) for the protons of the vinyl fragment in the 1 H NMR spectra.…”

Section: Resultsmentioning

confidence: 99%

“…Enamines 1a–e , bearing imidazole and isoxazole rings and several hydroxamoyl chlorides 2a–h bearing aryls with electron-withdrawing and releasing groups, pyridine and cyclohexane can be used for the synthesis of azolylisoxazoles 4a–p . Reactions of enamines with hydroxamoyl chlorides mainly lead to aromatic isoxazoles via intermediate 4,5-dihydro-5-aminoisoxazoles, which in some cases were isolated [23–24 26]. The latter could be transformed to aromatic isoxazoles by treatment with bases or acids [32].…”

Section: Resultsmentioning

confidence: 99%

“…We turned our attention to the reaction of enamines with nitrile oxides (or their precursors, hydroxamoyl chlorides). The reaction has been shown to take place regioselectively to form only one of two possible regioisomers [18–26]. …”

Section: Introductionmentioning

confidence: 99%

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Combined experimental and theoretical studies of regio- and stereoselectivity in reactions of β-isoxazolyl- and β-imidazolyl enamines with nitrile oxides

Efimov¹,

Shafikov²,

Беляев³

et al. 2016

Beilstein J. Org. Chem.

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Reactions of β-azolyl enamines and nitrile oxides were studied by both experimental and theoretical methods. (E)-β-(4-Nitroimidazol-5-yl), (5-nitroimidazol-4-yl) and isoxazol-5-yl enamines smoothly react regioselectively at room temperature in dioxane solution with aryl, pyridyl, and cyclohexylhydroxamoyl chlorides without a catalyst or a base to form 4-azolylisoxazoles as the only products in good yields. The intermediate 4,5-dihydroisoxazolines were isolated as trans isomers during the reaction of (E)-β-imidazol-4-yl enamines with aryl and cyclohexylhydroxamoyl chlorides. Stepwise and concerted pathways for the reaction of β-azolyl enamines with hydroxamoyl chlorides were considered and studied at the B3LYP/Def2-TZVP level of theory combined with D3BJ dispersion correction. The reactions of benzonitrile oxide with both E- and Z-imidazolyl enamines have been shown to proceed stereoselectively to form trans- and cis-isoxazolines, respectively. The preference of E-isomers over Z-isomers, driven by the higher stability of the former, apparently controls the stereoselectivity of the investigated cycloaddition reaction with benzonitrilе oxide. Based on the reactivity of azolyl enamines towards hydroxamoyl chlorides, a novel, effective catalyst-free method was elaborated to prepare 4-azolyl-5-substituted isoxazoles that are otherwise difficult to obtain.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Combined experimental and theoretical studies of regio- and stereoselectivity in reactions of β-isoxazolyl- and β-imidazolyl enamines with nitrile oxides

Efimov¹,

Shafikov²,

Беляев³

et al. 2016

Beilstein J. Org. Chem.

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“…Therefore, it was alternatively generated from aminopyrazole 5e by reaction with sodium nitrite in an aqueous solution of HBF 4 at low temperature (Scheme 2) and tetrafluoroborate salt 6e was used in situ in further studies. Enamines 8a-f were prepared by treatment of the corresponding 5-methylthiadiazole-4-carboxylate 7a,b or alkyl 5-methyl-3-arylisoxazole-4-carboxylates esters 7c-f with DMF-DMA in the presence of N-methylimidazole under reflux for six hours as has been reported earlier 33,34 (Scheme 3). Then with diazonium salts 6a-e and azolyl enamines 8a-f in hands we studied the reaction of 3-substituted pyrazole-5-diazonium salts 6a-e with azolyl enamines 8a-f (Scheme 4) and optimized the reaction conditions (Table 1).…”

Section: Resultsmentioning

confidence: 99%

“…33,34 General procedure for the synthesis of 3-aryl-1H-pyrazole-5-diazonium hydrosulfates (6a-d). A cooled solution of NaNO 2 (0.08 g, 1.2 mmol) in water (0.5 mL) was added dropwise to a stirring suspension of 3-aryl-5-aminopyrazole 5a-d (1.0 mmol) in 30% H 2 SO 4 (4 mL, 2 mmol) at 0 °C.…”

Section: Methodsmentioning

confidence: 99%