Cu-Catalyzed Dehydrogenative C-O Cyclization for the Synthesis of Furan-Fused Thienoacenes.

The first Cu-catalyzed dehydrogenative C-O cyclization for the synthesis of furan-fused thienoacenes is described. A variety of heteroacenes including a thieno[3,2-]furan or a thieno[2,3-]furan skeleton were synthesized by intramolecular C-H/O-H coupling. The use of a mixed solvent of -methyl-2-pyrrolidone, ethylene glycol monomethyl ether, and toluene was essential for suppressing side reactions and efficiently promoting the reaction.