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

Abstract

a-Formyl-a'-methyldipyrrylmethanes have been shown to react with a,a'- dicarboxydipyrrylmethanes to give hexapyrrenes which cyclize with copper acetate in pyridine to yield meso -pyrrolylporphyrins. However, if an a,a'-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 a-formyl-a'-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.