Practical Solvent-Free Ruthenium Trichloride-Mediated Benzannulation Approach to Fused Functionalized Arenes

The solvent-and ligand-free [2+2+2] ruthenium-promoted cycloaddition of alpha,omega-diynes and alkynes provides a facile and efficient strategy for the synthesis of substituted benzene-derived systems. The search for the optimal reaction conditions revealed the unprecedented catalytic activity of ruthenium trichloride for benzannulation reactions and this atom-economical process allowed the synthesis of fused arenes including dihydrobenzofurans, isoindolines, indanes in good to high yields. This practical protocol also gave rise to the preparation of pentasubstituted aromatic derivatives and was applied to the one-gram scale synthesis of a functionalized heterocycle.