Expeditious preparation of isoxazoles from Δ2-isoxazolines as advanced intermediates for functional materials (original) (raw)
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European Journal of Organic Chemistry, 2018
An efficient catalytic asymmetric synthesis of 3,4,5‐trisubstituted isoxazoline N‐oxides and regioselective synthesis of 3,4,5‐trisubstituted isoxazoles has been described. α‐Nitrocinnamates and α‐nitrobenzophenones were utilized as Michael acceptors respectively. Hydroquinine derived thiourea in combination with cesium carbonate was effective for the synthesis of isoxazoline N‐oxides whereas stoichiometric di‐isopropylethylamine (DIPEA) was the best choice for isoxazole synthesis. In both cases a range of aryl and heteroaromatic groups was tolerated.
Isoxazolines from Nitro Compounds: Synthesis and Applications
This paper reviews the construction of isoxazoline rings via 1,3-dipolar cycloaddition of nitrile oxides or nitronates, including silyl nitronates, generated from nitroalkanes, with alkenes. Recent studies on the mechanism and regiochemistry, inter- and intramolecular versions and asymmetric approaches to the cycloaddition are also dealt with in this review. A comparison of the nitrile oxide cycloaddition with silyl nitronate cycloaddition, especially their intramolecular versions, indicates the superiority of the silyl nitronate approach in providing the cycloadducts in greater yield and selectivity. Finally, various modes of cleavage of the isoxazoline ring to potentially useful synthetic intermediates are also discussed.
Journal of Molecular Structure, 2021
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Beilstein Journal of Organic Chemistry
Herein we report a method for the synthesis of 3,4,5-trisubstituted isoxazoles in water under mild basic conditions at room temperature via a [3 + 2]-cycloaddition of nitrile oxides and 1,3-diketones, β-ketoesters, or β-ketoamides. We optimized the reaction conditions to control the selectivity of the production of isoxazoles and circumvent other competing reactions, such as O-imidoylation or hetero [3 + 2]-cycloaddition. The reaction happens fast in water and completes within 1–2 hours, which provides an environmentally friendly access to 3,4,5-trisubstituted isoxazoles, an important class of structures found in numerous bioactive natural products and pharmaceuticals. Additionally, we optimized the reaction conditions to produce trifluoromethyl-substituted isoxazoles, a prevalent scaffold in biomedical research and drug discovery programs. We also proposed a plausible mechanism for the selectivity of the [3 + 2]-cycloaddition reaction to produce 3,4,5-trisubstituted isoxazoles. Not...
2021
A selective [3+2]-cycloaddition reaction of nitrile oxides and 1,3-diketones, β-ketoesters, or β-ketoamides in water without the need of a metal catalyst is described. The selectivity of the reaction can be controlled by the polarity of solvents in the presence of an appropriate base. The optimized reaction condition circumvents other reactions, such as O-imidoylation or hetero [3+2]-cycloaddition. The reaction happens fast in water to provide an environment friendly access to 3,4,5-trisubstituted isoxazoles, specifically acyl-substituted, ester-substituted, or amide-substituted isoxazoles, which are important structures found in numerous bioactive natural products and pharmaceuticals.