The oxidation of β-oxonitrones, derivatives of pyrroline and imidazoline, afforded symmetric dimers with a C-C bond and dehydrodimers with a C=C bond. Oxidation of the trifluoroacetyl imidazoline derivative afforded an asymmetric dimer. The oxidative dimerization of endocyclic β-oxonitrones, derivatives of pyrroline, proceeded much faster than that of exocyclic β-oxonitrones, derivatives of imidazoline. Imidazoline derivatives containing a perfluorophenyl or cyano group at the α-carbon atom on the nitrone group also underwent oxidative dimerization.