S 78 Spiro[4H-chromene-4,5-isoxazolines] and related compounds: Synthesis and reactivities [Electronic resource] / V. Ya. Sosnovskikh, A. Yu. Sizov, B. I. Usachev, M. I. Kodess, V. A. Anufriev // Russian Chemical Bulletin (Translation of Izvestiya Akademii Nauk, Seriya Khimicheskaya). - 2006. - Vol. 55, № 3. - P535-542 Рубрики: ХИМИЧЕСКИЕ НАУКИ Аннотация: Reactions of chromones with methyl ketoximes in the presence of lithium diisopropylamide follow the nucleophilic 1,2-addition mechanism to give spiro[4H-chromene-4,5?-isoxazolines] in good yields. The isoxazoline ring in spiro[4H-chromene-4,5?-isoxazolines] undergoes opening under the action of conc. H2SO4, yielding ?,?-unsaturated oximes. Their nitrosation and bromination lead to the corresponding spiroisoxazolines, while the Beckmann rearrangement, to ?,?-unsaturated amides. The latter are also formed directly from spiro[4H-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 \\\\Expert2\\nbo\\Russian Chemical Bulletin\\2006, 55 (3), 535.pdf |