Synthesis of p-Diiodobenzenes by [2+2+2] Cycloaddition

Significance

A new, high-yielding synthetic route to bicyclic diiodobenzenes is presented. Readily accessible dialkyne substrates were subjected to silver-catalyzed iododehydrogenation, followed by ruthenium-catalyzed [2+2+2] cycloaddition, leaving the carbon-iodine bonds untouched. Although acetylene was the most reactive partner, the use of both terminal and internal alkynes also resulted in good yields of products 2a-c. Tricyclic o-diiodobenzene 3 and diiodobiphenyl 4 were prepared by intramolecular cycloaddition of α,ω-diiodotriyne and -tetrayne precursors. Conjugated oligomers were synthesized by Suzuki, Sonoga­shira, and Heck couplings of the title compounds.