Recent Advances in Metal-Catalyzed Functionalization of Indoles

Indole is one of the most important heterocycles in organic synthesis, natural products, and drug discovery. Recently, tremendous advances in the selective functionalization of indoles have been reported. Although the most important advances have been powered by transition metal catalysis, exceedingly useful methods in the absence of transition metals have also been reported. In this review, we provide an overview of functionalization reactions of indoles that have been published in the last years with a focus on the most recent advances, aims, and future trends. The review is organized by the positional selectivity and type of methods used for functionalization. In particular, we discuss major advances in transition-metal-catalyzed C-H functionalization at the classical C2/C3 positions, transition-metal-catalyzed C-H functionalization at the remote C4/C7 positions, transition-metal-catalyzed cross-coupling, and transition-metal-free functionalization.