An Alternate Route of Transforming meso-Tetraarylporphyrins to Porpholactams, and Their Conversion to Amine-Functionalized Imidazoloporphyrins

A novel and efficient synthetic pathway toward known meso-tetraphenylporpholactams, also applicable to the synthesis of hitherto unknown and inaccessible meso-C6F5-substituted porpholactam, is detailed (dioxochlorin -> dioxochlorin urea adduct -> porpholactam). meso-Tetraphenylporpholactam was converted to an imidazoloporphyrin-alpha-triflate derivative that was demonstrated to be of utility for the generation of functionalized imidazoloporphyrins with a substituted amine adjacent to the outside N atom of the imidazole moiety (using pyridine, Et2NH, diethyliminodiacetic acetate, dipicolylamine (DPA), and cyclen). The DPA- and iminodiacetate-imidazoloporphyrin conjugates were structurally characterized. The chemosensing potential of the metal chelate-imidazoloporphyrin conjugates was evaluated, though their constrained metric parameters led to muted chemosensing responses to various divalent metal ions. The accessibility of the meso-arylporpholactams and the meso-tetraphenylimidazoloporphyrin triflate enables the continued exploration of porphyrin-like pyrrole-modified porphyrins that incorporate a nitrogen atom in place of a beta-carbon atom in their macrocycles.