Synthesis and functionalization of indoles through palladium-catalyzed reactions

The substituted indole nucleus [indole is the acronym from indigo (the natural dye) and oleum (used for the isolation)] is a structural component of a vast number of biologically active natural and unnatural compounds. The synthesis and functionalization of indoles has been the object of research for over 100 years, and a variety of well-established classical methods are now available. In the last 40 years or so, however, palladium catalyzed reactions, generally tolerant of a wide range of functionalities and therefore applicable to complex molecules, have achieved an important place in the arsenal of the practicing organic chemist. The impact of palladium chemistry of indoles in academic and medicinal chemistry communities has been extraordinary, as outlined by the number of studies developed in this area. Our aim is to try to provide a comprehensive and updated overview of recent developments in the palladium-catalyzed approaches to the preparation of indole derivatives with the emphasis on the rationale behind each synthetic procedure and the dependence of the results on a proper selection of reaction conditions.