Synthesis comproportionation

The porphyrins have excellent activity, but practical use has been hampered by their multistep synthesis and tendency to deactivate, usually by oxidative degradation from free-radical side reactions, or by alkylation of the pyrrole unit. The porphyrins also have a tendency to undergo comproportionation where the active epoxidizing intermediate forms a less active dimer through axial bonding as shown by Bruice [527]. Stability has been improved by the addition of bulky groups on the sides of the porphyrin [528,529], the synthesis of elaborate... 

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