Nitrolic acids: efficient precursors of nitrile oxides under neutral conditions

Nitrolic acids are prepared in good yields from primary nitroalkanes or primary alkyl bromides. Upon heating in THF, they afford the corresponding nitrile oxides under neutral conditions. In the presence of dipolarophiles, isoxazoles are obtained in yields up to 95%. For the less stable alkoxycarbonyl- and arylnitrolic acids the crude nitrolic acids can be directly engaged in the cycloaddition reaction.