Catalytic Syntheses of Five-membered Cyclic Compounds via -Unsaturated Early Transition Metal Alkylidene Intermediates

Cyclopentadienes and pyrroles are synthetically valuable five-membered cyclic compounds. Transition metal-catalyzed [2+2+1]-cycloaddition reactions involving two simple alkynes and a carbene or nitrene precursor offer an efficient and atom-economical route to these compounds. However, the scope of suitable carbene and nitrene precursors remains limited in such catalytic transformations. In this presentation, I will introduce our strategy employing cyclopropenes and azoarenes as novel substrates for unprecedented [2+2+1]-cycloaddition reactions with alkynes. These reactions are catalyzed by low-valent early transition metal complexes such as niobium and tungsten, and proceed via key intermediates featuring β-unsaturated metal alkylidene species.