5-Alkenyl-15-alkynylporphyrins have been obtained unexpectedly by [2+ 2] acid-catalyzed condensation of dipyrrylmethane and TMS propynal in addition to 5, 15-dialkynylporphyrin, and the unsymmetrical porphyrin can be converted to a butadiyne-linked dimer by selective desilylation of the alkynyl TMS.