Forgione, P., Bilodeau, F. et al. reported that heteroatoms containing a carboxylic acid also are tolerated by palladium monometallic systems and undergo decarboxylative cross coupling with aryl halides. In the proposed mechanism the initial step is oxidative addition of the aryl halide forming an aryl–palladium intermediate. Electrophilic palladation then occurs at carbon-3 of the heteroatom. From this intermediate there are two possible pathways for the cycle to continue on. The first is palladium migration from carbon-3 to carbon-2 along with the expulsion of carbon dioxide. This forms the aryl–palladium–heteroatom intermediate, which undergoes reductive elimination to form the final heteroaromatic compound. The second pathway only occurs when R is a proton. If this is the case, deprotonation occurs to regain aromaticity of the heteroatom. This intermediate then undergoes reductive elimination, coupling the aryl to the carbon-3 position of the heteroatom. As this compound still contains the carboxylic acid it is then free to re enter the catalytic cycle where it undergoes coupling at the carbon 2 position, along with the expulsion of carbon dioxide to form a biaryl heteroatom. As this pathway competes with the decarboxylation step, two products are formed making this reaction less selective. As a result, heteroatoms, which are substituted at the carbon 3 position and are more favored due to the higher level of control they provide.