1,3-dipolar cycloaddition of a nitronyl nitroxide-substituted alkyne to heteroaromatic n-imines

1,3-Dipolar cycloaddition of the triple bond in an ethynyl-substituted nitronyl nitroxide to heteroaromatic N-imines is described. The reaction opens a pathway to polyfunctional nitronyl nitroxides with pyrazolo[1,5-a]pyridine or related substituents. According to X-ray diffraction analysis, dihedral angles between the plane of the paramagnetic moiety and heteroaromatic cycle do not exceed 24°. Reactions between Cu(hfac)2 (hfac≤hexafluoroacetylacetonate ion) and a pyrazolo[1,5-a]pyridine-substituted radical produced a polymer chain complex with a 'head-to-tail' motif resembling that in breathing crystals.