Recent advances in Ugi reaction and its post-transformation strategies for crafting diverse indole frameworks

Indoles and their fused analogues are ubiquitous structural scaffolds present in a plethora of bioactive natural products and pharmaceutical compounds, showcasing their importance in drug design and delivery. Since the discovery of isocyanide-based multicomponent reactions (IMCRs), especially the Ugi reaction, there has been exponential growth in the development of new methodologies based on the post-modification of the Ugi reaction. This has led to the creation of diverse heterocyclic scaffolds, macromolecules, and natural products. This review summarizes the progression of Ugi-multicomponent reactions (MCRs) and their post-modification methods from 2012 to mid-2024. It highlights the documented protocols for constructing various indoles and hetero-fused indole derivatives in an enantioselective, regioselective, and chemoselective manner, emphasising their significance for medicinal chemists.

Challenge N- versus O-six-membered annulation: FeCl3-catalyzed synthesis of heterocyclic N,O-aminals

A new class of heterocyclic N,O-aminal and hemiaminal scaffolds was successfully obtained by means of a three-component reaction (3-CR) of 1,2-diaza-1,3-dienes (DDs), α-aminoacetals and iso(thio)cyanates. These stable imine surrogates are generated from key-substituted (thio)hydantoin intermediates through selective FeCl3-catalyzed intramolecular N-annulation.

Ethyl 4-hydroxy-2-oxo-1,2-dihydroquinoline-3-carboxylate in the smiles rearrangement reaction: straightforward synthesis of amino acid derived quinolin-2(1H)-one enamines

This paper describes the development of 4-hydroxy-2-oxo-1,2-dihydroquinoline-3-carboxylate compound as a heterocyclic enols containing a Michael acceptor so that it participates in an Ugi-type multicomponent condensation through a Smiles rearrangement in replacement of acid components. The new four-component containing 4-hydroxy-2-oxo-1,2-dihydroquinoline-3-carboxylate, aldehyde derivatives, amine derivatives and isocyanides process leads readily and efficiently to heterocyclic enamines. This report is an outstanding strategy for the preparation of new biologically structures containing peptidic or pseudo-peptidic with quinolin-2(1H)-one scaffolds.

Cobalt-catalyzed carbonylative synthesis of free (NH)-tetrahydro-β-carbolinones from tryptamine derivatives

A new cobalt-catalyzed carbonylative synthesis of free (NH)-tetrahydro-β-carbolinones from tryptamine derivatives has been developed. A variety of free (NH)-tetrahydro-β-carbolinones were produced in good yields. The oxidant, silver salt, can be recycled and reused.

Doebner-type pyrazolopyridine carboxylic acids in an Ugi four-component reaction

Substituted 1H-pyrazolo[3,4-b]pyridine-4- and 1H-pyrazolo[3,4-b]pyridine-6-carboxamides have been synthetized through a Doebner-Ugi multicomponent reaction sequence in a convergent and versatile manner using diversity generation strategies: combination of two multicomponent reactions and conditions-based divergence strategy. The target products contain as pharmacophores pyrazolopyridine and peptidomimetic moieties with four points of diversity introduced from readily available starting materials including scaffold diversity. A small focused compound library of 23 Ugi products was created and screened for antibacterial activity.

A Two-Step Multicomponent Synthetic Approach and Anti-inflammatory Evaluation of N-Substituted 2-Oxopyrazines

Inflammation is widely reported as a main factor for the development of chronic diseases such as cancer, diabetes, and even metabolic syndrome. Thus, the search for novel anti-inflammatory compounds is required. Herein we describe the synthesis of a collection of peptidic pyrazinones by a convenient approach involving a multicomponent isocyanide-based reaction followed by a tandem deprotection/oxidative cyclization step. This series of compounds were tested for their potential anti-inflammatory capacity in an in vivo murine model, and four compounds were identified to inhibit tetradecanoylphorbol acetate (TPA)-induced edema by more than 75 %. The two most active compounds, N-benzyl-2-(4-hydroxy-3,5-dimethoxyphenyl)-2-[2-oxopyrazin-1(2H)-yl]acetamide (10 o) and N-cyclohexyl-2-[2-oxopyrazin-1(2H)-yl]-2-[4-(trifluoromethyl)phenyl]acetamide (10 x), with methyl and trifluoromethyl groups, were also able to decrease myeloperoxidase activity and leukocyte infiltration. Moreover, 10 x decreased the thickness of TPA-treated mouse ears, as observed in histological analysis of the tissues.

β-Carbolinone Analogues from the Ugi Silver Mine

Here we describe a facile, tandem synthetic route for β-carbolinones, a class of natural products of high biological significance. Commercially available building blocks yield highly diverse analogues in just two simple steps.

Recent advances in the application of indoles in multicomponent reactions

Indoles are some of the most versatile and common nitrogen-based heterocyclic scaffolds and are frequently used in the synthesis of various organic compounds. Indole based compounds are very important among heterocyclic structures due to their biological and pharmaceutical activities. The last decade, in particular, has witnessed considerable activity towards the synthesis of indole derivatives due to the possibilities for the design of polycyclic structures by the incorporation of multiple fused heterocyclic scaffolds in an attempt to achieve promising new heterocycles with chemical and biomedical relevance. In this study, we provide an overview on recent applications of indole in the multicomponent reactions for the synthesis of various heterocyclic compounds during the period of 2012 to 2017.

Copper-Catalyzed Regioselective C-H Sulfonyloxylation of Electron-Rich Arenes with p-Toluenesulfonic Acid and Sulfonyloxylation of Aryl(mesityl)iodonium Sulfonates

Copper-catalyzed regioselective C-H sulfonyloxylation of electron-rich arenes with p-toluenesulfonic acid has been developed. Electron-rich benzene derivatives and heteroarenes can undergo this C-H sulfonyloxylation reaction to generate aryl tosylates. Furthermore, sulfonyloxylation of aryl(mesityl)iodonium sulfonates has also been investigated. Both aryl(mesityl)iodonium tosylates and triflates can react smoothly to get aryl sulfonates. The formed aryl sulfonates can be converted to phenols, as well as used as good partners of cross-coupling reactions.

Synthesis of 6-methyl-3,4-dihydropyrazinones using an Ugi 4-CR/allenamide cycloisomerization protocol

A two-step synthesis of 6-methyl-3,4-dihydropyrazinones from Ugi adducts and their transformation into pyrazino[2,1-a]isoindole and pyrazino[2,1-a]isoquinoline cores has been accomplished.

Concise approach to pyrrolizino[1,2-b]indoles from indole-derived donor–acceptor cyclopropanes

A direct approach to previously unexplored pyrrolizidino[1,2-b]indole system from indole-derived donor–acceptor cyclopropanes based on a sequence of three synthetic steps was developed.