Synthesis of Isoxazoline Ring from the 1,3-Dipolar Cycloaddition Reaction of Nitrile oxide and 2-Indeno[1,2-b]quinoxaline-11-ylidene-1-phenyl-ethanone

Nitrile oxide 1,afforded in situ from the reaction of dibromo formaldoxime and KHCO3,reacts with the olefin compounds to give bromoisoxazolines in satisfactory yields[1- 4]. Reaction of indeno[1,2-b]quinoxalin-11-one2 with 1-phenyl-2-(triphenylphosphanylidene)- ethanone3in ethanol resultedin 2-indeno[1,2-b]quinoxaline-11-ylidene-1- phenyl-ethanone (corresponding chalcone)4 at room temperature. 1,3-Dipolar cycloaddition of 2-indeno[1,2-b]quinoxalin-11-ylidene-1-phenyl-ethanone4 with nitrile oxide 1at room temperature in dichloromethane for 3 h formed a spiro compound with an isoxazole ring5(figure1).The structures were confirmed spectroscopically (IR, 1H- and 13C-NMR, and EI-MS) and by elemental analyses.