Recent Advances in the Synthesis of Indenes

Indenes constitute an important class of molecules which continue to attract interest from the synthetic organic chemists′ community because not only many natural and synthetic compounds embodying the indene skeleton display bioactivity or pharmaceutical activity but also because indenes find applications in material science, e.g. in photovoltaic solar cells and in the preparation of new fluorescent materials, and in the preparation of metal complexes with special catalytic activity. Many approaches have been exploited in the last four years to build this bicyclic system, the two most explored being cationic processes involving an intramolecular Friedel‐Crafts reaction and those in which a transition metal plays a key role in assembling the indene framework. In this review the results of the synthetic efforts toward indenes made in the 2016–2019 period are reviewed.