Oligocyclization of 2-(hydroxymethyl)pyrroles with electron-withdrawing groups at β-positions: formation and structural elucidation of porphyrinogens and hexaphyrinogens

Abstract

Acid-catalyzed oligomerization of 2-(hydroxymethyl)pyrroles bearing C₆F₅, 2,6-Cl₂C₆H₃, CF₃ and CO₂Et groups at β-positions was examined. The reaction of ethyl pyrrole-3-carboxylates gave a mixture of oligomers and type I isomers of porphyrinogens and hexaphyrinogens were isolated when the other β-substituents were sufficiently bulky, for example, mesityl, 2,6-Cl₂C₆H₃ and C₆F₅ groups. On the other hand, the pyrroles having other electron-withdrawing groups afforded porphyrinogens as the only isolable products.