MacDonald [2 + 2]-type condensation with vicinal diketones: synthesis and properties of novel spiro-tricyclic porphodimethenes.

[structure: see text] Acid-catalyzed [2 + 2] condensation reactions of polycyclic aromatic vicinal diketones including aceanthrenequinone, phenathrenequinone, and pyrene-4,5-dione with 5-mesityldipyrromethanes are outlined, and this methodology provides a flexible entry to spiro-tricyclic porphodimethenes. The porphodimethene products have been fully characterized, including X-ray structure analyses and fluorescence spectroscopy. In the case of the phenanthrenone-substituted macrocycle, the two spiro-locks can be ring-opened to form a trans-bis(2'-hydroxymethylbiphenyl)-substituted porphyrin.