Synthesis of indoles, indolines, and carbazoles via palladium-catalyzed C─H activation

The construction of indole, indoline, and carbazole heterocycles has been of significant interest in the synthetic community over the last century due to their prevalence in natural products and other biologically active compounds. In particular for indoles, many conventional methods developed to date require highly pre-functionalized arene precursors, diminishing their attractiveness as "green" syntheses. Carbon-hydrogen bond activation, on the other hand, presents an elegant solution to this problem and can achieve the construction of indoles and their derivatives from comparatively simpler arene precursors. In this short review, we discuss various approaches for preparing indoles, indolines, and carbazoles via palladium-catalyzed C─H bond activation, highlighting their reaction mechanisms and synthetic applications.