Cycloaddition/ring opening of 3-unsubstituted cyclic nitronates, isoxazoline and 5,6-dihydro-4H-1,2-oxazine N-oxides, as synthetic equivalents of functionalized nitrile oxides

omega-Halo-alpha-nitropropane and -butane are cyclized with a base to form cyclic nitronates as labile 1,3-dipoles. They can be trapped by a variety of monosubstituted ethenes to give 3-(2-hydroxyethyl)isoxazolines or perhydroisoxazolo[2,3-b]o-oxazines depending upon the ring size of nitronates. The latter ring-fused heterocycles are transformed by treatment with an acid into 3-(3-hydroxypropyl)isoxazolines in good yields. Therefore, these cyclic nitronates are useful synthetic equivalents of functionalized nitrile oxides. Isolation of 5,6-dihydro-4H-1,2-oxazine N-oxide and their regio- and stereoselective cycloadditions are also discussed. (C) 1998 Elsevier Science Ltd. All rights reserved.