Pd-Catalyzed Functionalization of Heterocycles Through C–H Activation

Pd-catalyzed transformations of heterocyclic compounds is an area of rapid growth that pushes the limit of chemical reactivity and is thus involved in a broad spectrum of redox organic transformations, such as cross-couplings, hydrogenation/dehydrogenation, hydrogenolysis, dehydrogenative coupling reactions and many other C-C and C-heteroatom bond forming reactions. This chapter presents a detailed overview of Pd-catalyzed C-H functionalizations of various heterocycles and their activation modes. Heterocyclic compounds, depending on their electronic nature, are often classified into π-excessive heterocycles and π-deficient heterocycles. Mechanistically, C-H functionalization of π-excessive heterocycles is often governed by electrophilic metalation, whereas in the case of π-deficient heterocycles, C-H activation mainly occurs via the directing group strategy. Moreover, we have covered a detailed discussion of the C-H functionalization of π-excessive and π-deficient heterocycles. Various activation modes have been discussed in the case of directing group-assisted C-H activation of π-deficient heterocycles. Combining different activation modes allows one to selectively functionalize at multiple positions around a heteroaromatic system.