Unprecedented Copper/Iron-Cocatalyzed Homocoupling of Propargyl Ethers to Conjugated Benzofurans

A dual-catalytic strategy has been developed to access conjugated enyne benzofurans via an unprecedented unsymmetrical homocoupling of <i>ortho</i>-iodophenyl propargyl ethers. An earth-abundant Cu-(II)/Fe-(III) dual-catalyst system enables high chemoselectivity and efficiency. Detailed mechanistic investigations, including control experiments and comprehensive density functional theory (DFT) studies, reveal that the reaction proceeds through <i>in situ</i> generation of Cu-(I) species, followed by an annulation event. The transformation culminates in a unique three-carbon homologation, involving a second propargyl unit and facilitated by the Fe-(III) cocatalyst. A broad array of enyne benzofuran derivatives bearing diverse functional groups was synthesized in up to 90% isolated yield. The synthetic practicality and wide applicability of this methodology are further demonstrated through gram-scale synthesis and postfunctionalization of the enyne moiety.