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.