Recent developments in the total synthesis of natural products using the Ugi multicomponent reactions as the key strategy

The total syntheses of selected natural products using different versions of the Ugi multicomponent reaction is reviewed on a case-by-case basis. The revision covers the period 2008-2023 and includes detailed descriptions of the synthetic sequences, the use of state-of-the-art chemical reagents and strategies, as well as the advantages and limitations of the transformation and some remedial solutions. Relevant data on the isolation and bioactivity of the different natural targets are also briefly provided. The examples clearly evidence the strategic importance of this transformation and its key role in the modern natural products synthetic chemistry toolbox. This methodology proved to be a valuable means for easily building molecular complexity and efficiently delivering step-economic syntheses even of intricate structures, with a promising future.

Brønsted Acid-Catalyzed Synthesis of 1,2,5-Trisubstituted Imidazoles via a Multicomponent Reaction of Vinyl Azides with Aromatic Aldehydes and Aromatic Amines

A facile and efficient approach to the synthesis of 1,2,5-trisubstituted imidazoles is developed via a multicomponent reaction under metal-free catalysis. Under Brønsted acid catalysis, the desired products can be obtained from readily available vinyl azides, aromatic aldehydes, and aromatic amines without generating any toxic waste. The convenient operations and high functional group compatibility indicate that this approach offers an attractive alternative method for the synthesis of imidazole derivatives.

New antifungal cycloheximide epimers produced by Streptomyces sp. YG7

A couple of new cycloheximide epimers, 13(α)-acetoxy-anhydroisoheximide (1) and 13(β)-acetoxy-anhydroisoheximide (2), together with six known compounds (3-8), were obtained from the cultures of Streptomyces sp. YG7. The structures were elucidated based on a comprehensive spectroscopic data analysis including 1D and 2D NMR, as well as HRESIMS, and by comparison with the literature. The X-ray crystal analysis of 1 further confirmed the structure. All the compounds were tested for antifungal activity. Compounds 1, 2 and 5-8 showed moderate Canidia albicans inhibitory activity, while 5 and 6 presented moderate Pyricularia oryzae inhibitory activity. [Formula: see text].

One-pot multi-component synthesis of new bis-pyridopyrimidine and bis-pyrimidoquinolone derivatives

A variety of bis-heterocycles such as bis(pyrimido[4,5-b]quinolone), bis(chromeno[3′,4':5,6]pyrido[2,3-d]pyrimidine), bis(pyrido[2,3-d:6,5-d']dipyrimidine), and bis(benzo[g]pyrimido[4,5-b]quinolone) derivatives were synthesized via one-pot, multi-component reaction of various 6-aminouracils or 6-aminothiouracils, terephthalaldehyde, and CH-acids such as 4-hydroxycoumarin, dimedone, 2-hydroxy-1,4-naphthoquinone, barbituric acid, and thiobarbituric acid in EtOH as a solvent at reflux. The mild conditions, fast rate of reaction, absence of catalyst, different functional group compatibility, simple operation and work-up involving no chromatographic process, are worth mentioning.

Ag2O-catalysed nucleophilic isocyanation: selective formation of less-stable benzylic isonitriles

Both primary and secondary benzylic isonitriles were exclusively produced by the Ag₂O-catalysed reaction of benzylic phosphates and trimethylsilyl cyanide without formation of the thermodynamically favoured regioisomers, benzylic nitriles.

Two decades of recent advances of Ugi reactions: synthetic and pharmaceutical applications

Multicomponent reactions (MCRs) are powerful synthetic tools in which more than two starting materials couple with each other to form multi-functionalized compounds in a one-pot process, the so-called “tandem”, “domino” or “cascade” reaction, or utilizing an additional step without changing the solvent, the so-called a sequential-addition procedure, to limit the number of synthetic steps, while increasing the complexity and the molecular diversity, which are highly step-economical reactions. The Ugi reaction, one of the most common multicomponent reactions, has recently fascinated chemists with the high diversity brought by its four- or three-component-based isonitrile. The Ugi reaction has been introduced in organic synthesis as a novel, efficient and useful tool for the preparation of libraries of multifunctional peptides, natural products, and heterocyclic compounds with stereochemistry control. In this review, we highlight the recent advances of the Ugi reaction in the last two decades from 2000–2019, mainly in the synthesis of linear or cyclic peptides, heterocyclic compounds with versatile ring sizes, and natural products, as well as the enantioselective Ugi reactions. Meanwhile, the applications of these compounds in pharmaceutical trials are also discussed.

We highlight the recent advances of the Ugi reaction in the last two decades from 2000–2019, mainly in the synthesis of linear or cyclic peptides, heterocyclic compounds with versatile ring sizes, and natural products, as well as the enantioselective Ugi reactions.

Rapid and catalyst free synthesis of new bis(benzo[g]chromene) and bis(pyrano[3,2-c]chromene) derivatives and optimization of reaction conditions using response surface methodology

4,4'-(1,4-phenylene)bis(2-(alkylamino)-3-nitro-4H-benzo[g]chromene-5,10-dione) and 4,4'-(1,4-phenylene)bis(2-(alkylamino)-3-nitropyrano[3,2-c]chromen-5(4H)-one) derivatives are synthesized by a one-pot, multi-component reaction of N-alkyl-1-(methylthio)-2-nitroethenamine (derived from the reaction of various amines and 1,1-bis(methylthio)-2-nitroethene) with terephthalaldehyde or isophthalaldehyde, and 2-hydroxy-1,4-naphthoquinone or 4-hydroxycoumarin in EtOH/H2O (85 : 15) as the solvent at 89 °C. Response surface methodology (RSM) is used to investigate the effect of reaction temperature and water content of aqueous ethanol on the product yields and reaction time. The notable features of this work are the optimization of reaction conditions with minimal experiments, absence of catalyst, good yields, simple work-up and the non-chromatographic purification of products.

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.

DBU-functionalized MCM-41-coated nanosized hematite (DBU-F-MCM-41-CNSH): a new magnetically separable basic nanocatalyst for the diastereoselective one-pot four-component synthesis of 2-(N-carbamoylacetamide)-substituted 2,3-dihydrothiophenes

Conversion of DBU from a nonrecoverable liquid base to a magnetically separable solid catalyst and its application for the diastereoselective multicomponent synthesis of 2-(N-carbamoylacetamide)-substituted 2,3-dihydrothiophenes.