Synthesis of indoles: recent advances

Published data of the last 10 years concerning the development of new and upgrading of known approaches to indole synthesis are integrated and analyzed. Modern versions of the classical syntheses such as the Fischer synthesis, Nenitzescu synthesis, Ullmann reaction, Leimgruber-Batcho synthesis, Reissert synthesis, Bartoli reaction, Madelung synthesis and Cadogan-Sundberg reaction are considered. The presented new approaches include transformations of heterocycles, synthesis from o-alkynylanilines, reductive cyclization of nitrobenzene derivatives, synthesis with the use of arynes and catalysis by N-heterocyclic carbenes. The final Section summarizes original methods for the synthesis of indoles other than those listed above; they are classified in terms of the nature of the forming bond (C-C, C-N). Rarely used methods based on benzene ring construction in pyrrole derivatives are discussed separately.