Exploring the limitations of the MacDonald ‘3 + 1’ condensation in the preparation of porphyrins with fused electron-withdrawing heterocyclic rings: Synthesis of a bis(thiadiazolo)benzoporphyrin and a related benzocarbaporphyrin

[Display omitted] A pyrrole ethyl ester with a fused bis(thiadiazolo)benzo unit was prepared by reacting 4-nitrobenzo[1,2-c:3,4-c’]bis(1,2,5)thiadiazole with ethyl isocyanoacetate in the presence of a non-nucleophilic base. Cleavage of the ester moiety, followed by reaction with a chloromethylpyrrole in refluxing pyridine, afforded a tripyrrane and subsequent acid-catalyzed condensation with pyrrole or indene dialdehydes gave porphyrinoids incorporating fused electron-deficient heterocyclic units.