Rational approach to the synthesis of meso-meso (5,5') linked bis-porphyrins

A novel approach for the synthesis of 5,5'-directly linked metal-free bis-porphyrins is reported; McMurry type coupling of dipyrroketones (e.g. 1) leads to 1,1,2,2-tetra(2-pyrrolyl)ethene 2, which after tetra-formylation (to give 3) and MacDonald macrocyclization with a 1,9-di-unsubstituted dihydrodipyrrin 4, affords the 5,5'-bis-porphyrin 5.