Photochemical Double 5-exo Cyclization of Alkenyl-Substituted Dithienylacetylenes: Efficient Synthesis of Diarylated Dithienofulvalenes

摘要

Pentafulvalene is a hydrocarbon that possesses two cyclo-pentadiene rings formally cross-conjugated through an exo-cyclic double bond. Whereas the parent pentafulvalene is thermally unstable, it can be stabilized by ring fusion or the introduction of peripheral substituents. Pentafulvalene exhibits characteristic redox properties, because it forms a stable radical anion and a dianion with Hiickel 6π aromaticity. Utilization of its dianion as a ligand for metal complexes has been extensively studied. The other notable feature is its high electron-accepting character, which renders itself being a potent core skeleton for electron-accepting π-conjugated materials, such as n-type semiconducting materials. For example, Wudl and co-workers have recently reported the application of arene-fused pentafulvalene derivatives as an electron-transporting material for organic photovoltaic cell.