Synthesis of functionalized diarylbenzofurans via Ru-catalyzed C-H activation and cyclization under air: rapid access to the polycyclic scaffold of diptoindonesin G

An efficient method was developed for synthesis of 2,3-diarylbenzofuran-4-carboxylic acids from m-hydroxybenzoic acids and alkynes via Ru-catalyzed C-H alkenylation and aerobic annulation, in which air was employed as a mild oxidant. This method is compatible for various substrates with high regioselectivity for the C-H bonds. The obtained products can be transformed to polycyclic compounds via intramolecular Friedel-Crafts acylation. This protocol was successfully applied for total synthesis of diptoindonesin G, a natural product with a benzofuran-containing tetracyclic scaffold and potent biological activities.