Novel chemical modifications at the 4-position of chromones. Synthesis and reactivity of 4H-chromene-4-spiro-5′-isoxazolines and related compounds |
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| Authors: | Vyacheslav Ya. Sosnovskikh Boris I. Usachev Mikhail I. Kodess |
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| Affiliation: | a Department of Chemistry, Ural State University, 620083 Ekaterinburg, Russian Federation
b Institute of Organic Synthesis, Ural Branch of the Russian Academy of Sciences, 620219 Ekaterinburg, Russian Federation |
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| Abstract: | Reactions of chromones with dilithiooximes proceed via nucleophilic 1,2-addition to give, on acidification, 4H-chromene-4-spiro-5′-isoxazoline derivatives in high yields. On treatment with concentrated H2SO4 the isoxazoline ring of this novel spiroannulated heterocyclic system opens to give α,β-unsaturated oximes, which undergo nitrosation, bromination, and the Beckmann rearrangement to the corresponding spiroisoxazolines and α,β-unsaturated amides, respectively. The latter can be obtained directly by the Beckmann rearrangement of 4H-chromene-4-spiro-5′-isoxazolines. |
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| Keywords: | Chromones Dilithiooximes 4H-Chromene-4-spiro-5&prime -isoxazolines α,β-Unsaturated oximes Beckmann rearrangement Nitrosation Bromination |
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