Recent advances in the development of one-pot/multistep syntheses of 3,4-annulated indoles

Many naturally occurring indole alkaloids and biologically interesting compounds, such as the ergot alkaloids, contain the C-3/C-4-annulated indole scaffold. These important compounds are often tetracyclic structures with multiple stereocentres. While a lot of research has been directed towards the total syntheses of the naturally occurring indole alkaloids, most synthetic strategies involve intensive multistep procedures with low overall yields. Recently there has been significant progress in the development of "cascade", "tandem" or "domino" type processes, which involve multiple bond-forming reactions in one pot. The ability to install complexity into a chemical structure in a single operation is a powerful tool that can be applied to complex polycyclic C-3/C-4-annulated indole-containing compounds. This review will cover the past decade of development of one-pot/multistep reactions for the synthesis of C-3/C-4-annulated indoles employing on organo- and transition metal catalysis. (C) 2020 Elsevier Ltd. All rights reserved.