Bidirectional iterative synthesis of alternating benzene-furan oligomers towards molecular wires.

Reaction of propargylic dithioacetal 2a with BuLi gives the sulfur-substituted allenyllithium 3a which is allowed to react with a dialdehyde to yield the corresponding alternating benzene-furan oligoaryls 6. Functional group transformation converts the ester groups in 6 to dialdehyde 8 which can be used for the synthesis of higher homologues towards molecular wires. A combination of this furan annulation, Heck reaction and Sonogashira coupling leads to a variety of benzene-furan-alkene/alkyne conjugated oligomers of precise length.