Lewis Acid Mediated Aminobenzannulation Reactions of δ-Ketoalkynes: Synthesis of 1-Aminocarbazoles and 9-Aminopyrido[1,2-a]indoles

Recent synthetic strategies for the construction of functionalized carbazoles and their heterocyclic motifs enabled by Lewis acids

This article demonstrates recent innovative cascade annulation methods for preparing functionalized carbazoles and their related polyaromatic heterocyclic compounds enabled by Lewis acid catalysts. Highly substituted carbazole scaffolds were synthesized via Lewis acid mediated Friedel-Crafts arylation, electrocyclization, intramolecular cyclization, cycloaddition, C-N bond-formations, aromatization and cascade domino reactions, metal-catalyzed, iodine catalyzed reactions and multi-component reactions. This review article mainly focuses on Lewis acid-mediated recent synthetic methods to access a variety of electron-rich and electron-poor functional groups substituted carbazole frameworks in one-pot reactions. Polyaromatic carbazole and their related nitrogen-based heterocyclic compounds were found in several synthetic applications in pharma industries, energy devices, and materials sciences. Moreover, the review paper briefly summarised new synthetic strategies of carbazole preparation approaches will assist academic and pharma industries in identifying innovative protocols for producing poly-functionalized carbazoles and related highly complex heterocyclic compounds and discovering active pharmaceutical drugs or carbazole-based alkaloids and natural products.

One-Pot Arylative Benzannulation of 2-Carbonyl-3-propargyl Indoles with Boronic Acids Leading to Arylated Carbazoles

Arylative annulation of 2-carbonyl-3-propargyl indoles with boronic acids under sequential palladium/triflic acid catalysis is described. The present strategy to provide di- and triaryl carbazoles in one pot involves benzannulation through difunctionalization of alkynes. The strategy showed a good substrate scope with respect to boronic acids as well as 2-carbonyl-3-propargyl indoles to afford the corresponding carbazoles in decent yields.

MediaChrom: Discovering a Class of Pyrimidoindolone-Based Polarity-Sensitive Dyes

A small library of six polarity-sensitive fluorescent dyes, nicknamed MediaChrom, was prepared. This class of dyes is characterized by a pyrimidoindolone core fitted out with a conjugated push-pull system and a carboxy linker for a conceivable coupling with biomolecules. The optimized eight-step synthetic strategy involves a highly chemo- and regioselective gold-catalyzed cycloisomerization reaction. The photophysical properties of MediaChrom dyes have been evaluated in-depth. In particular, the MediaChrom bearing a diethylamino as an electron-donating group and a trifluoromethyl as an electron-withdrawing group displays the most interesting and advantageous spectroscopic features (e.g., absorption and emission in the visible range and a good quantum yield). Promising results in terms of sensitivity have been obtained in vitro on this dye as a membrane/lipophilic probe and as a peptide fluorescent label.

Titanocene-catalyzed multicomponent coupling approach to diarylethynyl methanes

A titanocene-catalyzed multicomponent coupling to provide diarylethynyl methanes is described. By combining the multifunctionality of Cp(2)TiCl(2) with the traceless dielectrophilicity of aryl aldehydes, all-carbon tertiary centers are obtained in 55-99% yield.

Indol-2-yl ethanones as novel indoleamine 2,3-dioxygenase (IDO) inhibitors

Indoleamine 2,3-dioxygenase (IDO) is a heme dioxygenase which has been shown to be involved in the pathological immune escape of diseases such as cancer. The synthesis and structure-activity relationships (SAR) of a novel series of IDO inhibitors based on the indol-2-yl ethanone scaffold is described. In vitro and in vivo biological activities have been evaluated, leading to compounds with IC(50) values in the micromolar range in both tests. Introduction of small substituents in the 5- and 6-positions of the indole ring, indole N-methylation and variations of the aromatic side chain are all well tolerated. An iron coordinating group on the linker is a prerequisite for biological activity, thus corroborating the virtual screening results.