Bromination of tetrapyrrolic scaffolds: a sustainable approach
A sustainable procedure developed for the bromination of organic substrates, such as olefins and small aromatic rings, has been applied to porphyrin derivatives. The synthetic method, based on a V(V) or Mo(VI) catalyzed reaction, occurs in a two-phase medium and uses cheap and environmental friendly reagents such as KBr and H2O2 as the bromine source and primary oxidant respectively. Compared to the classical protocols for porphyrinoid bromination, this approach is based on milder and safer reaction conditions. The selective formation of mono or polybrominated substrates has been achieved by accurate tuning of key parameters (H2O2 and KBr amount, catalyst). While with vanadium good results to obtain partially substituted porphyrins have been gained, full peripheral functionalization can be obtained with either vanadium or molybdenum catalysis depending on the metal ion coordinated to the inner core.