Synthesis of Fused Dibenzofuran Derivatives via Palladium-Catalyzed Domino C-C Bond Formation and Iron-Catalyzed Cycloisomerization/Aromatization.

A range of tetracyclic dibenzofuran derivatives bearing a variety of functional groups was readily synthesized via a two-stage domino strategy starting from propargyl ethers of 2-halo phenol derivatives. The first stage in the strategy involves Pd(0)-catalyzed domino intramolecular carbopalladation/Suzuki coupling via 5-exo-dig cyclization onto the alkyne, leading to 3-methylene-2,3-dihydrobenzofuran derivatives. In the second stage of the domino strategy, an iron(III)-catalyzed cycloisomerization and aromatization reaction produces tetracyclic benzofuran derivatives. This two-step sequence provides efficient access to diversely substituted polycyclic dibenzofuran derivatives in high yields and in an atom-efficient and environmentally friendly manner. Moreover, this strategy was also successfully used for the synthesis of a naturally occurring tetracyclic dibenzofuran, β-brazan.