Rh-Catalyzed [2 + 2 + 2] Cycloaddition between Aryl-Substituted 1,6-Diynes and Monoynes: Controlling Alkyne Reactivity with Hexafluoroisopropanol

The transition metal-catalyzed [2 + 2 + 2] cycloaddition between aryl-substituted 1,6-diynes and monoynes is a valuable transformation for synthesizing π-conjugated compounds. The formation of metallacyclopentadiene from the 1,6-diyne is entropically favored. However, monoynes and 1,6-diynes can react with this intermediate, leading to the undesired homocycloadduct of the 1,6-diyne in addition to the desired cross-cycloadduct. Thus, the synthesis of tetraarylbenzenes by controlling chemoselectivity using diaryl-substituted 1,6-diynes, which have a flexible tether and are prone to the homo-[2 + 2 + 2] cycloaddition, and less reactive bulky diarylacetylenes is challenging. Here, we report that a cationic Rh(I)/BINAP catalyst enables the cross-[2 + 2 + 2] cycloaddition between diaryl-substituted monoynes and 1,6-diynes with the flexible tether at room temperature, giving the corresponding tetraarylbenzenes in high yields. The electronic property of the terminal substituents of the 1,6-diynes and monoynes affects the chemoselectivity. Additionally, incorporating hexafluoroisopropanol (HFIP) into the reaction solvent effectively controls alkyne reactivity, thereby suppressing the homocycloaddition of 1,6-diynes and favoring cross-cycloaddition.