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

Abstract

Oligothiophenes are important organic molecules in a number of burgeoning industries as semi‐conducting materials due to their extensive π‐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.