Spiro[4H-chromene-4,5′-isoxazolines] and related compounds: Synthesis and reactivities |
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| Authors: | V Ya Sosnovskikh A Yu Sizov B I Usachev M I Kodess V A Anufriev |
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| Institution: | (1) A. M. Gorky Ural State University, 51 prosp. Lenina, 620083 Ekaterinburg, Russian Federation;(2) I. Ya. Postovskii Institute of Organic Synthesis, Ural Division of the Russian Academy of Sciences, 20 ul. S. Kovalevskoi, 620219 Ekaterinburg, Russian Federation |
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| Abstract: | Reactions of chromones with methyl ketoximes in the presence of lithium diisopropylamide follow the nucleophilic 1,2-addition
mechanism to give spiro4H-chromene-4,5′-isoxazolines] in good yields. The isoxazoline ring in spiro4H-chromene-4,5′-isoxazolines] undergoes opening under the action of conc. H2SO4, yielding α,β-unsaturated oximes. Their nitrosation and bromination lead to the corresponding spiroisoxazolines, while the
Beckmann rearrangement, to α,β-unsaturated amides. The latter are also formed directly from spiro4H-chromene-4,5′-isoxazolines] under the action of PCl5. N-Substituted acetophenone hydrazones in the presence of lithium diisopropylamide react at the C(4) atom of 2-trifluoromethylchromone,
while acetophenone anil under the same conditions, at the C(2) atom.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 516–522, March, 2006. |
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| Keywords: | chromones dilithio oximes and dilithio hydrazones spiro[4H-chromene-4 5′ -isoxazolines] and spiro[4H-chromone-4 5′ -pyrazolines] α β -unsaturated oximes and amides Beckmann rearrangement nitrosation bromination |
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