Cobalt-catalyzed alkyne cyclotrimerization and crossed [2 + 2 + 2] cycloadditions are developed in a plug flow reactor. The protocol generally uses 5 mol % of Co2(CO)8 and is scalable at least at multigram scale. Efficient and scalable use of Co2(CO)8 for crossed reactions of diynes and alkynes has hardly any precedent.
A practical and convenient solvent-free iridium-catalyzed [2+2+2] cycloaddition of alpha,omega-diynes and alkynes to prepare fused arenes has been developed. The method has shown high efficiency as isoindolines, dihydroisobenzofurans and indanes have been synthesized in good to excellent yields.