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.