Enynone-enabled migratory insertion and Schmittel cyclization cascade for the synthesis of furan-fused fluorenes

A new method for the synthesis of furan-/benzo-fused fluorenes through copper(I)-catalyzed coupling of conjugated enynones or α-diazocarbonyl compounds with dialkynylbenzenes has been developed. This process includes 5-exo-dig cyclization, carbene migratory insertion, Schmittel cyclization and 1,5-H transfer. The obvious advantages of wide substrate scopes, mild reaction conditions, and high atom efficiency make this system highly appealing for the construction of six-substituted benzofuran-embedded fluorenes in a one-pot manner.