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-b]­furan or a thieno­[2,3-b]­furan skeleton were synthesized by intramolecular C–H/O–H coupling. The use of a mixed solvent of N-methyl-2-pyrrolidone, ethylene glycol monomethyl ether, and toluene was essential for suppressing side reactions and efficiently promoting the reaction. Double C–O cyclization was also conducted to afford highly π-expanded furan-fused thienoacenes.

A one-pot procedure for the synthesis of thienyl thioethers is described. Several thienyl thioethers were synthesized by a TfOH-promoted Friedel–Crafts-type cyclization, a subsequent nucleophilic attack by an arenethiol, and dehydration. This protocol was successfully applied to the synthesis of thienoacene derivatives by using a Pd-catalyzed dehydrogenative cyclization.