Versatile synthesis of 3,4-b diheteropentalenes

We describe a new route for the synthesis of thieno[3,4-b]thiophene, alkyl derivatives thereof, seleno[3,4-b]thiophene, and thieno[3,4-b]furan made from inexpensive starting materials, such as thiophene-2-carboxylic acid and furan-2-carboxylic acid. Such fused heterocycles are of great interest for low band gap organic semiconductors and applications including OLEDs, organic photovoltaic cells, and electrochromics.