Preferential Formation of Cyclic Trimers by Palladium‐Catalyzed Oxidative Coupling Reactions of 2,18‐Diethynylporphyrins

And palladium makes three: In contrast to the formation of cyclic dimers in the Cu-mediated reaction, Pd-catalyzed oxidative coupling of 2,18-diethynylporphyrins preferentially produced cyclic trimers (see scheme). A porphyrin hexamer with a doubly 1,3-butadiyne-bridged conjugated trimeric core and directly meso-appended peripheral porphyrin substituents was also synthesized.