Porphyrin quinones with sterically demanding 3,6-di-tert-butyl-o-quinones were synthesized for electron transfer studies. In the presence of atmospheric oxygen the covalently free base porphyrin-o-quinones are oxidized to muconic acid anhydride and 3,6-dicarbonyl-derivatives. In contrast to the well established chemistry of catecholase models based on 3,5-substituted quinones this is the first example for oxidative ring expansion of 3,6-disubstituted o-quinones.