Pictet-Spengler Synthesis of Quinoline-Fused Porphyrins and Phenanthroline-Fused Diporphyrins

Doubly and quadruply quinoline-fused porphyrins were effectively synthesized through a reaction sequence consisting of Suzuki-Miyaura coupling of beta-borylated porphyrins with 2-iodoaniline and subsequent Pictet-Spengler cyclization. These quinoline-fused porphyrins display red-shifted absorption bands and higher electron-accepting abilities. This synthetic protocol also allowed the synthesis of phenanthroline-fused porphyrin dimers, which bound either a Ni-II or Zn-II cation. The resultant metal complexes displayed further red shifted absorption spectra and molecular twists to effect an almost perpendicular arrangement of the two porphyrins.