1,3-Dipolar Cycloaddition Route to Isoxazoline N-Oxides

Significance

A general method for the synthesis of substituted isoxazoline N-oxides via a 1,3-dipolar cycloaddition of simple olefins with in situ generated 1-halo-O-silyl nitronates, followed by halo­silane elimination, in moderate to good overall yield is reported. Stable bromonitro analogues undergo slow reaction thereby limiting the scope to terminal olefins, whereas the more reactive fluoro­nitro analogues, although unstable to isolation, undergo cycloaddition with disubstituted olefins. Calculated relative rate constants (Gaussian) for the cycloaddition step agree with the experimental data.