 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.