The chemistry of pyrrolic compounds. XX. Bilenes-b as intermediates in the synthesis of porphyrins related to protoporphyrin IX. meso-Pyrrolylporphyrins

α-Formyl-α'-methyldipyrrylmethanes have been shown to react with α,α'- dicarboxydipyrrylmethanes to give hexapyrrenes which cyclize with copper acetate in pyridine to yield meso-pyrrolylporphyrins. However, if an α,α'-dicarboxydipyrrylmethane is decarboxylated in N,N-dimethylformamide and the product converted into its monoimmonium salt (Vilsmeier-Haack intermediate) with benzoyl chloride this salt with an α-formyl-α'-methyldipyrrylrnethane affords a bilene-b which with copper acetate-pyridine gives a normal porphyrin. This latter procedure has been adapted to prepare tetrapyrroles of the protoporphyrin IX type. A synthesis of pemptoporphyrin dimethyl ester is reported.