When the nickel 1-substituted octa-β-alkyltetradehydrocorrins are heated, they rearrange to nickel corroles containing geminal substituents at C-3 rather than at C-2 as previously thought. The use of a mixture of ethyl and methyl substituents has shown that the migration of the 1-substituent proceeds in a two-stage process involving C-2, and the order of migratory aptitude of the various substituents is allyl > ethoxycarbonyl > ethyl > methyl. The rearrangements probably occur by a sigmatropic mechanism.