Rh-Catalyzed [3 + 2] Cascade Annulation of Aromatic Acids with Oxabicyclic Alkenes: Direct Access to Planar Benzo[ a ]fluorenones

Abstract

A rhodium-catalyzed [3 + 2] annulation of aromatic acids and 7-oxabenzonorbornadienes has been developed, enabling a facile one-step synthesis of planar π-conjugated polycyclic benzo[a]fluorenone featuring an ordered herringbone packing motif with slipped stacking in moderate to excellent yields. The reaction proceeds under simple conditions via a carboxyl-directed naphthylation, which comprises direct addition of the C–H bond to the alkenes with subsequent dehydration, followed by an intramolecular Friedel–Crafts reaction. This protocol features simple reaction conditions and a broad substrate.