Transition-metal-catalyzed cyclization of [a,c] biladiene salts as an efficient route to the synthesis of alkyl porphyrins

Several alkyl porphyrins have been synthesized by cyclization of different 1,19-dimethyl [a,c]biladiene dihydrobromides, catalyzed by rhodium, ruthenium and chromium salts in buffered alcoholic media. When the reactions were carried out without base, a drastic reduction of porphyrin yields was observed. No substantial differences were observed on changing the solvent. A different reaction pathway was seen when the 1,19-substituent groups were bulkier than methyl. © 1990.