Successive Pd‐Catalyzed Decarboxylative Cross‐Couplings for the Modular Synthesis of Non‐Symmetric Di‐Aryl‐Substituted Thiophenes

Oligothiophenes are important organic molecules in a number of burgeoning industries as semi-conducting materials due to their extensive pi-conjugation and charge transport properties. Typically, non-symmetric, di-aryl-substituted thiophenes are prepared by the successive formation of Grignards, organotin, and/or boronic acid intermediates that can be subsequently employed in cross-coupling reactions. While reliable, these approaches present synthetic difficulties due to the reactivity of organo-metallic/pseudo-metallic species, and produce considerable amounts of waste due to necessary pre-functionalization. We have developed a decarboxylative cross-coupling route as an effective strategy for the modular and less wasteful synthesis of a wide range of non-symmetric, di-arylthiophenes. This method uses a thiophene ester building block for successive decarboxylative palladium-catalyzed couplings that allows for the efficient synthesis and evaluation of the opto-electronic properties of a library of candidate semi-conductors with functional groups that could be challenging to access using previous routes.