Ester as a blocking group for palladium-catalysed direct forced arylation at the unfavourable site of heteroaromatics: simple access to the less accessible regioisomers

The use of esters as blocking groups at the C2 position on a range of 3-substituted 5-membered ring heteroaromatics such as thiophenes or furans, allows control of the regioselectivity for the palladium-catalysed direct arylation at C5-H. This arylation can be followed by easy decarboxylation. This method allows sequential catalytic C5 arylation, decarboxylation and catalytic C2 arylation reactions.