Selective synthesis of 5-alkenyl-15-alkynyl-porphyrin and 5,15-dialkynyl-porphyrin by 2+2 acid-catalyzed condensation of dipyrrylmethane and TMS propynal

One of 5-alkenyl-15-alkynyl-porphyrin and 5,15-dialkynyl-porphyrin was prepared selectively by 2+2 acid-catalyzed condensation of bicyclo[2.2.2]octadiene-fused dipyrrylmethane and TMS propynal in the presence of BF3·OEt2 only by the choice of the solvent. The alkenyl group was expected to be obtained by a protonation followed by intramolecular 1,2-hydride transfer from methine position of porphyrinogen.