The synthesis of covalently linked porphyrin dimers and trimers is described. Mono‐ and dihydroxyporphyrins were synthesized by transeslerifying 5,10,15,20‐tetra(4‐carbomethoxy‐phenyl)porphyrin with ethylene glycol. The mixture of transesterified porphyrins were separated by preparative thin layer chromatography. Metal derivatives were made of the mono‐ and dihydroxyporphyrins and these were reacted with the acid chloride of a monocarboxyporphyrin to yield hybrid dimers and trimers containing one melalloporphyrin and either one or two free base porphyrins. The structures and purity of the dimers and trimers were established by measuring the absorbance spectra, nmr spectra, and molecular weight by gel permeation chromatography.

The photochemistry of 4-pyrones has been shown to be remarkably dependent on the number of substituents present in the pyrone ring. Thus although the dimerization of 2,6-disubstituted-4-pyrones is a welldocumented photochemical reaction,1-2 Ishibi has (1) P.

Bei Bestrahlung der Pyry.lium‐Kationen (I) in 96%iger Schwefelsäure entstehen die entsprechenden 2‐Hydroxy‐pyrylium‐Kationen, die bei nachfolgender Neutralisation in die entsprechendenPyrone (II) übergehen.

In der Porphyrin‐ Reihe dienen der Tetracarbonsäureester (I) sowie der Monoester (III) als Ausgangsmaterial.