The ring expansion of a dimethyl-substituted vinylcyclobutene derivative by metal complexes that can undergo an inner-sphere electron transfer

The ring expansion of a dimethyl-substituted vinylcyclobutene derivative to the corresponding dimethyl-substituted cyclohexadiene or aromatic compound was studied. It was found that metal complexes of Ni(I), Ti(III), Sm(II), and Fe(II), which can undergo an inner-sphere electron-transfer reaction, allow the rearrangement to occur at room temperature. Other oxidation states of these metals and complexes that can only undergo an outer-sphere electron-transfer process do not promote this ring expansion reaction.