Reactions of heterocyclic paramagnetic aldonitrone, 2,2,5,5-tetramethyl-3-imidazoline-1-oxyl 3-oxide, with alkynes

The reactions of heterocyclic paramagnetic aldonitrone, viz., 2,2,5,5-tetra methyl-3-imidazoline-1-oxyl 3-oxide, with mono- and disubstituted alkynes a fford unstable isoxazoline derivatives. The reactions with monosubstituted alkynes yield predominantly 5-substituted regioisomers. The resulting isoxa zoline derivatives are readily (and often spontaneously) converted into ena minoketones, viz., imidazolidine-1-oxyl derivatives. In the presence of tol an, the title paramagnetic aldonitrone gives a dimer in which one imidazoli ne ring undergoes profound transformation. The structure of the resulting d imer was established by X-ray diffraction analysis.