Synthetic Methods for 3,4‐Fused Tricyclic Indoles via Indole Ring Formation

Abstract

3,4-Fused tricyclic indole frameworks are found in various bioactive natural products and pharmaceuticals. The development of an efficient synthetic method for this structural motif has therefore attracted attention in the field of synthetic organic chemistry and medicinal chemistry. Herein, we summarize recent advances in the synthesis of 3,4-fused tricyclic indoles. This class of synthetic methods can be roughly classified into two categories: methods using functionalized indole derivatives as starting materials to construct a fused medium-sized ring (Types A-D: Category I), and methods of constructing a 3,4-fused tricyclic indole skeleton via indole ring formation (Types E-G: Category II). In this focus review, synthetic methods for 3,4-fused tricyclic indoles classified as Category II methods are highlighted, following a brief overview of the Category I methods. 2 3 4 5 6 7 8

A novel and robust heterogeneous Cu catalyst using modified lignosulfonate as support for the synthesis of nitrogen-containing heterocycles

“…With the catalysts in hand, we investigated their catalytic activity in organic reactions. Tricyclic indole alkaloids bearing 3,4-fused seven-membered rings have attracted much attention because of their interesting molecular architectures and important biological activities [ 32 – 33 ]. Here the three-component reaction of 4-aminoindole ( 1a ), 4-methylbenzaldehyde ( 2a ) and diethyl acetylenedicarboxylate ( 3a ) was performed to construct the seven-membered indole ring system with the aid of the LS-FAS-Cu catalyst, and the results are summarized in Table 1 .…”

Regioselectivity of the SEAr-based cyclizations and SEAr-terminated annulations of 3,5-unsubstituted, 4-substituted indoles

“…Herein, we summarize these literature reports, with a special attention on the regiochemistry. Noteworthy is that although three reviews on the synthesis of 3,4-fused indoles have been published in the last decade [5][6][7], this is the first time the regioselectivity of the S E Ar-based/terminated cyclization and annulation reactions of 3,5-unsubstituted, 4-substituted indolesis is sytematized as a dedicated topic.…”

Tandem Annulations of Propargylic Alcohols to Indole Derivatives

“…Due to the importance of indole derivatives, considerable effort has been made to develop highly efficient synthetic methodologies to access these compounds [3] . Among these methods, synthetic approaches based on cascade reactions [3g,4] are highly powerful as they tend to avoid multiple work‐up steps as well as purifications of all intermediates. On the other hand, propargylic alcohols, bearing alkynyl and hydroxyl functional groups, have emerged as promising feedstock materials for the construction of carbo‐ and heterocycles [5] .…”