Stability of electron deficient activated nitronates under neutral and Lewis acid catalyzed conditions. Facile nitronate cycloaddition reactions to the magnesium alkoxides of allylic alcohols leading to isoxazolidines and isoxazolines

Article abstract of DOI:10.1016/S0040-4039(98)01902-9

N-Methoxy-N-[bis(methoxycarbonyl)methylene]amine N-oxide and N-methoxy- N-(methoxycarbonylmethylene)amine N-oxide as electron-deficient activated nitronates, show an exceptionally high reactivity to the magnesium alkoxides of allylic alcohols. Isoxazolidines or isoxazolines are formed as cycloadducts, depending upon the substitution pattern of the allylic alcohols. When the latter C-monosubstituted nitronate is treated with a catalytic amount of boron trifluoride etherate, the corresponding nitrile oxide is smoothly generated through β-elimination of methanol.