Dirhodium-Catalyzed [2 + 2 + 2] Cycloaddition of 1,6-Diynes and Alkynes

A facile method for the construction of fused arenes has been developed through dirhodium-catalyzed [2 + 2 + 2] cycloaddition, which represents a new application of dirhodium complexes. This protocol is convenient to handle without the addition of extra ligands and reductants and tolerates a broad range of functional groups. Mechanistic studies revealed that the two-electron oxidation process, carboxylate ligand departure, and heteroatom coordination-promoted [2 + 2 + 2] cycloaddition were possibly involved.