Ugi-Smiles couplings: new entries to N-aryl carboxamide derivatives

Stefano Marcaccini: a pioneer in isocyanide chemistry

Stefano Marcaccini was one of the pioneers in the use of isocyanide-based multicomponent reactions in organic synthesis. Throughout his career at the University of Florence he explored many different faces of isocyanide chemistry, especially those geared towards the synthesis of biologically relevant heterocycles. His work inspired many researchers who contributed to other important developments in the field of multicomponent reactions and created a school of synthetic chemists that continues today. In this manuscript we intend to review the articles on isocyanide multicomponent reactions published by Dr. Marcaccini and analyse their influence on the following works by other researchers. With this, we hope to highlight the immense contribution of Stefano Marcaccini to the development of isocyanide chemistry and modern organic synthesis as well as the influence of his research on future generations. We believe that this review will not only be a well-deserved tribute to the figure of Stefano Marcaccini, but will also serve as a useful inspiration for chemists working in this field.

N-Oxide-Induced Ugi Reaction: A Rapid Access to Quinoline-C2-amino Amides via Deoxygenative C(sp2)-H Functionalization

A logic-based replacement of the carboxylic acid component of the Ugi reaction by quinoline N-oxides has been developed. In this approach, the carboxylic isostere, quinoline N-oxide, plays a vital role by shifting the equilibria toward the product side with irreversible addition onto the C2-position of the N-oxide. Thus, aldehydes react with amines, isocyanides, and quinoline N-oxides to furnish quinoline four-component Ugi adducts. The unique reactivity of N-oxides with Ugi components opens an efficient synthetic route for the preparation of biologically active compounds.

Three-Component Reactions of 3-Arylidene-3H-Indolium Salts, Isocyanides and Amines

A multicomponent reaction of isocyanides with aryl(indol-3-yl)methylium salts and amines has been found. A series of aryl(indol-3-yl)acetimidamides was obtained in up to 96% yields. In the case of ethyl isocyanoacetate, the reaction is followed by cyclization to form 3,5-dihydro-4H-imidazol-4-one derivatives.

Implementing parallel arithmetic via acetylation and its application to chemical image processing

Chemical mixtures can be leveraged to store large amounts of data in a highly compact form and have the potential for massive scalability owing to the use of large-scale molecular libraries. With the parallelism that comes from having many species available, chemical-based memory can also provide the physical substrate for computation with increased throughput. Here, we represent non-binary matrices in chemical solutions and perform multiple matrix multiplications and additions, in parallel, using chemical reactions. As a case study, we demonstrate image processing, in which small greyscale images are encoded in chemical mixtures and kernel-based convolutions are performed using phenol acetylation reactions. In these experiments, we use the measured concentrations of reaction products (phenyl acetates) to reconstruct the output image. In addition, we establish the chemical criteria required to realize chemical image processing and validate reaction-based multiplication. Most importantly, this work shows that fundamental arithmetic operations can be reliably carried out with chemical reactions. Our approach could serve as a basis for developing more advanced chemical computing architectures.

The status of isocyanide-based multi-component reactions in Iran (2010-2018)

Isocyanides as key intermediates and magic reactants have been widely applied in organic reactions for direct access to a broad spectrum of remarkable organic compounds. Although the history of these magical compounds dates back more than 100 years, it still has been drawing widespread attention of chemists who confirmed their versatility and effectiveness. Because of their wide spectrum of pharmacological, industrial and synthetic applications, many reactions with the utilization of isocyanides are reported in the literature. In this context, Iranian scientist played a significant role in the growth of isocyanides chemistry. The present review article covers literature from the period starting from 2010 onward and encompasses new synthetic routes and organic transformation involving isocyanides by Iranian researchers. During this period, a diverse range of isocyanide-based multi-component reactions (I-MCRs) has been reported such as a new modification of Ugi, post-Ugi, Passerini and Groebke-Blackburn-Bienayme condensation reactions, isocyanide-based [1 + 4] cycloaddition reactions, isocyanide-acetylene-based MCRs, isocyanide and Meldrum's acid-based MCRs, several unexpected reactions besides green mediums and novel catalytic systems for the synthesis of diverse kinds of pharmaceutically and industrially remarkable heterocyclic and linear organic compounds. This review also emphasizes the neoteric applications of I-MCR for the synthesis of valuable peptide and pseudopeptide scaffolds, enzyme immobilization and functionalization of materials with tailorable properties that can play important roles in the plethora of applications.

Fixing CO2 into β-oxopropylcarbamates in neat condition by ionic gelation/Ag(i) supported on dendritic fibrous nanosilica

In this research, a novel approach to produce a novel nanocatalyst, AgBr supported on an ionic gelation (IG)-based nanomaterial, was developed through the aqueous coprecipitation approach for the dendritic fibrous nanosilica (DFNS) production and the wet impregnation method for IG coating, taking into account TPP as the cross-linking agent. In addition, DFNS/IG@Ag(i) had heterogeneous features that contributed to the quick improvement of the catalyst by filtration separation. The catalytic activity of DFNS/IG@Ag(i) was examined to synthesize β-oxopropylcarbamates through a multicomponent coupling of CO2, amines and propargyl alcohols in moderate conditions. The DFNS/IG@Ag(i) NPs were completely investigated by taking advantage of TG, TEM, FESEM and FT-IR spectroscopy analyses. The DFNS/IG@Ag(i) nanocatalyst indicated high stability in the reaction for five cycles without considerable loss of some properties like activity, which could be because of the high loading of IG on the catalyst surface.

Multicomponent Reaction Toolbox for Peptide Macrocyclization and Stapling

In the past decade, multicomponent reactions have experienced a renaissance as powerful peptide macrocyclization tools enabling the rapid creation of skeletal complexity and diversity with low synthetic cost. This review provides both a historical and modern overview of the development of the peptide multicomponent macrocyclization as a strategy capable to compete with the classic peptide cyclization methods in terms of chemical efficiency and synthetic scope. We prove that the utilization of multicomponent reactions for cyclizing peptides by either their termini or side chains provides a key advantage over those more established methods; that is, the possibility to explore the cyclic peptide chemotype space not only at the amino acid sequence but also at the ring-forming moiety. Owing to its multicomponent nature, this type of peptide cyclization process is well-suited to generate diversity at both the endo- and exo-cyclic fragments formed during the ring-closing step, which stands as a distinctive and useful characteristic for the creation and screening of cyclic peptide libraries. Examples of the novel multicomponent peptide stapling approach and heterocycle ring-forming macrocyclizations are included, along with multicomponent methods incorporating macrocyclization handles and the one-pot syntheses of macromulticyclic peptide cages. Interesting applications of this strategy in the field of drug discovery and chemical biology are provided.

Post-Ugi Cyclization for the Construction of Diverse Heterocyclic Compounds: Recent Updates

Multicomponent reactions (MCRs) have proved as a valuable tool for organic and medicinal chemist because of their ability to introduce a large degree of chemical diversity in the product in a single step and with high atom economy. One of the dominant MCRs is the Ugi reaction, which involves the condensation of an aldehyde (or ketone), an amine, an isonitrile, and a carboxylic acid to afford an α-acylamino carboxamide adduct. The desired Ugi-adducts may be constructed by careful selection of the building blocks, opening the door for desired post-Ugi modifications. In recent times, the post-Ugi transformation has proved an important synthetic protocol to provide a variety of heterocyclic compounds with diverse biological properties. In this review, we have discussed the significant advancements reported in the recent literature with the emphasis to highlight the concepts and synthetic applications of the derived products along with critical mechanistic aspects.

Iminium Ion and N-Hydroxyimide as the Surrogate Components in DEAD-Promoted Oxidative Ugi Variant

A practical metal-free oxidative Ugi-type three-component assembly has been achieved efficiently, employing a tertiary-amine-derived iminium ion as an imine surrogate, N-hydroxyimide as an acid surrogate, and DEAD as an oxidant. This dual-surrogate Ugi variant proceeded with a broad substrate scope and desired functional group tolerance, leading to a wide range of N-alkyl- N-acyl aminophthalimide and N-alkyl- N-acylaminosuccinimide derivatives in good isolated yields.

N–N bond formation in Ugi processes: from nitric acid to libraries of nitramines

N–N bond formation in Ugi processes: from nitric acid to libraries of nitramines.

Application of heterocyclic aldehydes as components in Ugi-Smiles couplings

Efficient one-pot Ugi–Smiles couplings are reported for the use of furyl-substituted aldehyde components. In the presence of these heterocyclic aldehydes, reactions tolerated variations in amine components and led to either isolated N-arylamide Ugi–Smiles adducts or N-arylepoxyisoindolines, products of tandem Ugi–Smiles Diels–Alder cyclizations, in moderate yields. A thienyl-substituted aldehyde was also a competent component for Ugi–Smiles adduct formation.

Optimized Conditions for Passerini-Smiles Reactions and Applications to Benzoxazinone Syntheses

Initial conditions disclosed for the Passerini-Smiles reaction are associated with a lack of efficiency that has prevented chemists from using it since its discovery. We wish to report herein our thorough study in the development of new experimental conditions for this coupling between electron-poor phenols, isocyanides, and carbonyl derivatives. These new conditions have been applied to several synthetic strategies towards benzoxazinones.

Solution- and Solid-Phase Macrocyclization of Peptides by the Ugi-Smiles Multicomponent Reaction: Synthesis of N-Aryl-Bridged Cyclic Lipopeptides

A new multicomponent methodology for the solution- and solid-phase macrocyclization of peptides is described. The approach comprises the utilization of the Ugi-Smiles reaction for the cyclization of 3-nitrotyrosine-containing peptides either by the N-terminus or the lysine side-chain amino groups. Both the on-resin and solution cyclizations took place with good to excellent efficiency in the presence of an aldehyde and a lipidic isocyanide, while the use of paraformaldehyde required an aminocatalysis-mediated imine formation prior to the on-resin Ugi-Smiles ring closure. The introduction of a turn motif in the peptide sequence facilitated the cyclization step, shortened the reaction time, and delivered crude products with >90% purity. This powerful method provided a variety of structurally novel N-aryl-bridged cyclic lipopeptides occurring as single atropisomers.

Transition-metal-free synthesis of indole-fused dibenzo[b,f][1,4]oxazepines via Smiles rearrangement

A one-pot transition-metal-free approach for the synthesis of indole-fused dibenzo[b,f][1,4]oxazepines from 2-(1H-indol-2-yl)phenol and 1,2-dihalobenzenes or 2 halonitroarenes has been developed.

Cu-catalyzed one-pot synthesis of fused oxazepinone derivatives via sp2 C–H and O–H cross-dehydrogenative coupling

An efficient Cu-catalyzed cascade reaction protocol was developed for the synthesis of fused oxazepinone derivatives via sp² C–H and O–H cross-dehydrogenative coupling.

Highly stereoselective synthesis of natural-product-like hybrids by an organocatalytic/multicomponent reaction sequence

In an endeavor to provide an efficient route to natural product hybrids, described herein is an efficient, highly stereoselective, one-pot process comprising an organocatalytic conjugate addition of 1,3-dicarbonyls to α,β-unsaturated aldehydes followed by an intramolecular isocyanide-based multicomponent reaction. This approach enables the rapid assembly of complex natural product hybrids including up to four different molecular fragments, such as hydroquinolinone, chromene, piperidine, peptide, lipid, and glycoside moieties. The strategy combines the stereocontrol of organocatalysis with the diversity-generating character of multicomponent reactions, thus leading to structurally unique peptidomimetics integrating heterocyclic, lipidic, and sugar moieties.

Cu(i)-catalyzed microwave-assisted synthesis of 1,2,3-triazole linked with 4-thiazolidinones: a one-pot sequential approach

A novel copper(i) catalyzed, microwave-assisted, one-pot, four-component, sequential reaction has been developed for the synthesis of 3-phenyl-2-[4-{(1-phenyl-1H-1,2,3-triazol-4-yl)methoxy}phenyl]thiazolidin-4-ones.

Solvent switchable cycloaddition: a (one-pot) metal-free approach towards N-substituted benzo[e]- or [f]isoindolones via C(sp(2))-H functionalization

The tuning of selective ring closure is a nontrivial challenge in synthetic organic chemistry. Herein we report a solvent switchable metal-free [4 + 2] cycloaddition approach via Csp(2)-H functionalization. The protocol is highly atom economical with water being the only by-product, delivering N-substituted benzo[e]- or [f]isoindolones in high yields.

Predicting new Ugi-smiles couplings: a combined experimental and theoretical study

Following our previous mechanistic studies of multicomponent Ugi-type reactions, theoretical calculations have been performed to predict the efficiency of new substrates in Ugi-Smiles couplings. First, as predicted, 2,4,6-trichlorophenol experimentally gave the corresponding aryl-imidate. Theoretical predictions of nitrosophenols as good acidic partners were then successfully confirmed by experiments. In the latter case, the reaction offers a new access to benzimidazoles.

Double Smiles rearrangement of Passerini adducts towards benzoxazinones

A new straightforward access to benzoxazinones based on a three-component coupling is presented here.

Post-Ugi gold-catalyzed diastereoselective domino cyclization for the synthesis of diversely substituted spiroindolines

An Ugi four-component reaction of propargylamine with 3-formylindole and various acids and isonitriles produces adducts which are subjected to a cationic gold-catalyzed diastereoselective domino cyclization to furnish diversely substituted spiroindolines. All the reactions run via an exo-dig attack in the hydroarylation step followed by an intramolecular diastereoselective trapping of the imminium ion. The whole sequence is atom economic and the application of a multicomponent reaction assures diversity.

Regio- and diastereoselective synthesis of β-lactam-triazole hybrids via Passerini/CuAAC sequence

Passerini (P-3CR) and Passerini-Smiles reactions were investigated in azetidine-2,3-diones, affording the corresponding 3,3-disubstituted-β-lactams with complete diastereoselectivity in high yields. The study has been carried out using different isocyanides, carboxylic acids, and phenols showing the scope of both reactions. In addition, the regioselective synthesis of highly functionalized β-lactam-triazole hybrids has been developed via a Passerini/CuAAC sequence. Interestingly, the use of dialkynes/diazides or trialkynes/triazides as linkers in the CuAAC step has allowed the synthesis of C(2) and C(3) symmetric β-lactam-triazole hybrids, respectively.