Controlling conformations and physical properties of meso-tetrakis(phenylethynyl)porphyrins by ring fusion: synthesis, properties and structural characterizations

The boron trifluoride-catalyzed Rothemund condensations of phenylpropargylaldehyde with 4,7-dihydro-4,7-ethano-2H-isoindole or 3, 4-diethylpyrrole in dichloromethane at low temperature give 5,10,15,20-tetrakis(phenylethynyl) porphyrins bearing bicyclo [2.2.2] octadiene and octaethyl substituents, respectively. The former undergoes a retro Diels Alder reaction to afford 5, 10,15,20-tetrakis(phenylethynyl) benzoporphyrin quantitatively. The different conformations of the porphyrin periphery were determined by X-ray diffraction and their redox and spectroscopic properties have been investigated.