Let the best ring win: Selective macrocycle formation through Pd-catalyzed or Cu-mediated alkyne homocoupling

Competition is good: The reported "Pd" homocoupling procedure is now a viable alternative to the traditional Cu-mediated reaction for the formation of diacetylenic macrocycles. From the same starting material, use of Cu(OAc)2 or [PdCl2(dppe)]/I2 (dppe = 1,2-bis(diphenylphosphanyl)ethane) leads to selective formation of either the bis[15]- or bis[14]annulenes (see scheme).