Synthesis and characterization of meso-tetraphenylporphyrin-corrole unsymmetrical dyads

Flat and gable meso-tetraphenylporphyrin-corrole heterodimers have been synthesized following a stepwise approach. The macrocyclic precursor for both isomers is a functionalized meso-tetraphenylporphyrin (TPP) bearing a formyl group at one of the peripheral phenyl groups. The preparation of these starting materials has been improved with respect to the previously reported method. Acidic condensation with pyrrole 8 allows the preparation of a TPP-dipyrromethane intermediate. Subsequent decarboxylation followed by reaction with formylpyrrole 2 affords the corresponding TPP-a,c-biladiene species. Final cyclization of this intermediate affords the desired heterodimer. Attempts to use the functionalized corrole 5 as starting material were unsuccessful, as this corrole failed to condense with pyrrole and benzaldehyde. This synthetic approach provides new examples of tetrapyrrolic heterodimers, which can represent useful biomimetic models to study photochemical processes.