Environmentally Benign Arylations of 5-Membered Ring Heteroarenes by Pd-Catalyzed C-H Bonds Activations

The palladium-catalyzed functionalization of 5-membered ring heteroaromatics, through a C-H bonds activation, for access to arylated heteroaromatics represent a very attractive alternative to more classical cross-coupling reactions, as it saves steps and reduces the amount of wastes. Despite these advantages, these transformations initially suffered from major limitations in terms of sustainable chemistry concerning the reaction media, the nature of the catalyst, the catalyst loading, the aryl source or the regioselectivity control. Tremendous improvements allowing more sustainable reaction conditions using greener solvents, new aryl sources or employing easily removable catalysts and lower catalyst loadings have been described during the last decades. This review summarizes some of the most important contributions made in these directions.