General and Scalable Approach to A 2 B- and A 2 BC-Type Porphyrin Phosphonate Diesters
Résumé
A two-step reaction sequence for accessing meso-(dialkoxyphosphoryl) porphyrins from readily available trans-A(2)-type porphyrins was developed. This approach involves bromination and subsequent palladium-catalyzed phosphonylation. Optimal conditions for both steps were identified after exploration of various reaction parameters such as solvent, temperature and catalyst. A series of dialkoxyphosphoryl-substituted A2B-porphyrins Zn3(a-g) bearing electron-donating, electron-withdrawing or sterically bulky substituents at the meso-aryl groups were prepared in overall yields close to 40 %. These compounds, being air-stable and soluble in most organic solvents, are valuable synthetic intermediates because they can be readily transformed into functionalized trans-A(2)BC-type porphyrins through regioselective functionalization at the unsubstituted meso position of the macrocycle. Therefore, this approach offers considerable promise for application to the synthesis of trans-A(2)BC-type porphyrins, including water-soluble derivatives, push-pull chromophores and bis(porphyrin)s.