Ullmann-Type Intramolecular C–O Reaction Toward Thieno[3,2‑b]furan Derivatives with up to Six Fused Rings

A new strategy for the efficient synthesis of thieno­[3,2-b]­benzofuran derivatives (15 examples) was achieved on the basis of successive regioselective intermolecular Suzuki and newly developed intramolecular Ullmann C–O reactions in up to a 70% overall yield. The fast intramolecular C–O reaction can be realized by an efficient catalytic combination of CuI/1,10-phenanthroline in up to a 97% yield. This method is suitable for the construction of highly fused thieno­[3,2-b]­furan-containing heterocycles including DTBDF and TTDBF. The π–π and hydrogen-bonding interactions observed for the C8-DTBDF single crystal suggest its great potential for OFET applications in the near future.