Transition-Metal-Catalyzed C-H Functionalization for the Synthesis of Substituted Pyridines

The direct functionalization of pyridine and related azine derivatives through carbon-carbon bond-forming reactions is reviewed. Various transformations that use a variety of transition-metal catalysts are covered, including alkylation, alkenylation, arylation, and acylation. In addition to the conventionally observed C2-selectivity for these transformations, recent developments involve selective introduction of newly formed carbon-carbon bonds to the C3- and C4-positions of pyridine and azine nuclei. The reaction scope and a proposed mechanism for each transformation are briefly summarized.