Unconventional Passerini Reaction toward α-Aminoxy-amides

Innovative synthesis of drug-like molecules using tetrazole as core building blocks

Tetrazole is widely utilized as a bioisostere for carboxylic acid in the field of medicinal chemistry and drug development, enhancing the drug-like characteristics of various molecules. Typically, tetrazoles are introduced from their nitrile precursors through late-stage functionalization. In this work, we propose a novel strategy involving the use of diversely protected, unprecedented tetrazole aldehydes as building blocks. This approach facilitates the incorporation of the tetrazole group into multicomponent reactions or other chemistries, aiding in the creation of a variety of complex, drug-like molecules. These innovative tetrazole building blocks are efficiently and directly synthesized using a Passerini three-component reaction (PT-3CR), employing cost-effective and readily available materials. We further showcase the versatility of these new tetrazole building blocks by integrating the tetrazole moiety into various multicomponent reactions (MCRs), which are already significantly employed in drug discovery. This technique represents a unique and complementary method to existing tetrazole synthesis processes. It aims to meet the growing demand for tetrazole-based compound libraries and novel scaffolds, which are challenging to synthesize through other methods.

Exploring Phthalimide as the Acid Component in the Passerini Reaction

Multicomponent reactions, particularly the Passerini reaction, serve as efficient tools for the synthesis of druglike molecules and the creation of compound libraries. Despite the effectiveness of the Passerini reaction, the limited alternatives to the crucial carboxylic acid component pose a structural constraint. Here, we have discovered that the phthalimide moiety and its derivatives react in the Passerini reaction as an acid component. We explored their potential in synthesizing diverse and intricate molecules. The phthalimide moiety stands out as a favorable building block due to its oxidative stability, heat-stable characteristics, and resistance to solvents. Our approach introduces a novel perspective to multicomponent reactions by incorporating NH-based acid components, addressing the ongoing need for the development of innovative molecular scaffolds.

3-Trifluoroacetyl-quinolin-2(1H)-ones as Carbonyl and Acid Surrogates in the Passerini-/Ugi-Type Reaction

Herein, we report tailored 3-trifluoroacetyl-quinolin-2(1H)-ones (1) as carbonyl and acid surrogates in Passerini- and Ugi-type reactions for the synthesis of α-trifluoromethyl-α-hydroxy carboxamides (4) and α-trifluoromethyl α-amino acids (6) in high yields, respectively. The reaction proceeds under mild reaction conditions via an exocyclic carboximidate intermediate (3). The amide group in compound 1 acts as an acid component as well as a reversible oxygen nucleophile to facilitate the reaction.

Two decades of recent advances of Passerini reactions: synthetic and potential pharmaceutical applications

This perspective describes the applications of Passerini reactions in the last two decades from 2000 to 2021 in pharmaceutical applications and synthesis of peptides, natural products, macrocycles, dendrimers, and versatile types of heterocycles.

Three Component Synthesis of β‑Aminoxy Amides

A multicomponent reaction for the synthesis of β‑aminoxy amides is described. In this reaction, N-hydroxamic acids, yna-mides and aldehydes could assemble efficiently to deliver structurally diverse β‑aminoxy amides under the...

Passerini-type reaction of boronic acids enables α-hydroxyketones synthesis

Multicomponent reactions (MCRs) facilitate the rapid and diverse construction of molecular scaffolds with modularity and step economy. In this work, engagement of boronic acids as carbon nucleophiles culminates in a Passerini-type three-component coupling reaction towards the synthesis of an expanded inventory of α-hydroxyketones with skeletal diversity. In addition to the appealing features of MCRs, this protocol portrays good functional group tolerance, broad substrate scope under mild conditions and operational simplicity. The utility of this chemistry is further demonstrated by amenable modifications of bioactive products and pharmaceuticals as well as in the functionalization of products to useful compounds.

Multicomponent reactions enable the rapid construction of diverse molecular scaffolds with modularity and step economy. In this work, the authors report the use of boronic acids as carbon nucleophiles in a Passerini-type three-component coupling reaction towards an expanded inventory of α-hydroxyketones.

Functional Isocyanide-Based Polymers

Research interest in the isocyanide-based reaction can be traced back to 1921 when the Passerini reaction was first reported. However, most of these research efforts did not lead to important progress in the synthesis of isocyanide-based polymers (IBPs). The major challenge resides in the lack of highly efficient polymerization methods, which limits large-scale preparation and applications. Modern organic chemistry provides efficient access to develop functional IBPs on the basis of isocyanide chemistry. However, it is still challenging to prepare the IBPs with small molecular isocyanide reaction. Our investigations into catalyst exploration and polymerization methodology have prompted the synthesis of a series of IBPs. Two classes of isocyanide monomers can be used for the construction of IBPs. The first class includes monomers with a single isocyanide. Novel catalysts for the synthetic chemistry of isocyanide allow the introduction of functional pendants into the linear polymer chains. This molecular functionalization endows the polymers with an array of new functional properties. For example, the incorporation of a chromophore on the polymeric side chain provides novel functional properties, such as aggregation-induced emission and optical activity. Diisocyanide monomers can be also utilized for the construction of heterocyclic, spiro-heterocyclic, and bispiro-heterocyclic polymers in the polymeric backbones. A new concept of "multi-component spiropolymerization" has been developed for the preparation of spiropolymers using the catalysis-free one-pot reaction. Proper structural design allows for the preparation of a heterocyclic polymeric chain with natural bioactivity and biological compatibility, generating new IBPs with biofunctionalities.In this Account, we discuss progress mainly made in our lab and related fields for the design of isocyanide monomers, exploration of new catalysts, and optimization of reaction conditions. The subsequent section discusses the characteristic properties and applications of selected examples of these functional polymers, mainly focusing on their optical applications. We have investigated the UV-sensitive IBPs that could potentially be used for lithography applications. One-pot highly efficient polymerization of diisocyanides and CO₂ under mild conditions can provide a new method for realizing the reuse of CO₂ and reducing the greenhouse effect. Through a combination of structural modifications, IBPs bearing dimethylbenzene moieties exhibit characteristics of black materials that can be potentially utilized as pyroelectric sensors, thermal detectors, and optical instruments. Most recently, our group synthesized a spiro-heterocyclic IBP with clusterization-triggered emission properties that can be used to discriminate cancer cells from normal cells and provides a new method for the treatment of cancer. The studies reviewed in this Account suggest that polymerization with isocyanide chemistry can be implemented in diverse functional macromolecules and materials.

Isocyanide-based consecutive Bargellini/Ugi reactions: an efficient method for the synthesis of pseudo-peptides containing three amide bonds

Isocyanide-based consecutive Bargellini/Ugi multicomponent reactions as a combinatorial strategy have been developed for the synthesis of new class of pseudo-peptides. Via Bargellini reaction 3-carboxamido-isobutyric acids are prepared using acetone, chloroform, sodium hydroxide, and isocyanides. Then, using Ugi multicomponent reaction strategy, pseudo-peptides containing three amide bonds are synthesized using the Bargellini reaction product, aldehydes, amines, and isocyanides. This is an efficient and eco-friendly approach for easy access to wide variety of structurally diverse, drug-like pseudo-peptides from cheap and readily available precursors in high yields.

Cu-catalyzed cross-coupling of methyl ketones and pyridin-2-amines for the synthesis of N-(2-pyridyl)-α-ketoamides

An efficient copper-catalyzed strategy for the synthesis of α-ketoamides via cross-coupling of methyl ketones and pyridin-2-amines is described. This transformation has provided a simple process for the formation of C−N and C=O bonds to prepare α-ketoamides, which are important substrates and intermediates for the preparation of fine chemicals. The reaction mechanism is investigated, which suggests that the reaction proceeds via a radical pathway.

Ultrasound-Facilitated Direct meta-C-H Functionalization of Arenes: A Time-Economical Strategy under Ambient Temperature with Improved Yield and Selectivity

The horizon of ultrasound-assistance has been expanded to palladium-catalyzed distal C-H functionalization of arenes. Compared to thermal conditions, operationally simple ultrasound mediated distal C-H functionalization occurred with a shorter reaction time and enhanced reactivity of reactants to give superior yields with improved selectivity both in terms of meta:others and mono:di. A wide variety of meta-functionalizations such as olefination, alkylation, acetoxylation, allylation and cyanation were successfully carried out under ambient temperature.

Dimerization–cyclization reactions of isocyanoaryl-tethered alkylidenecyclobutanes via a triplet biradical mediated process

A triplet biradical mediated dimerization–cyclization reaction of isocyanoaryl-tethered alkylidenecyclobutanes to construct macrocyclic skeletons including dihydroquinoline and quinoline units has been reported.

With unprotected amino acids to tetrazolo peptidomimetics

Here we describe the direct usage of C,N-unprotected amino acids in Ugi-tetrazole reactions to produce a novel class of acid-tetrazole compounds. Surprisingly, only the tetrazole Ugi product is found and not traces of other possible Ugi type reactions. Based on this reaction pathway we have designed the synthesis of novel tetrazole-peptidomimetics. A high level of structural diversity can be achieved using this isocyanide based multicomponent reaction (IMCR), providing a platform for the production of functionalized building blocks for novel bioactive molecules and nontraditional scaffolds which previously were not accessible.

Hexafluoroisopropanol as the Acid Component in the Passerini Reaction: One-Pot Access to β-Amino Alcohols

A new Passerini-type reaction in which hexafluoroisopropanol functions as the acid component is reported. The reaction tolerates a broad range of isocyanides and aldehydes, and the formed imidates can be reduced toward β-amino alcohols under mild and metal-free conditions. In addition, the imidate products were shown to undergo an unprecedented retro-Passerini-type reaction under microwave conditions, providing valuable mechanistic information about the Passerini reaction and its variations.

Synthesis of Highly Substituted Imidazole Uracil Containing Molecules via Ugi-4CR and Passerini-3CR

The synthesis of uracil/thymine containing tetra/trisubstituted imidazole derivatives was demonstrated using Ugi/Passerini-reaction followed by a postcyclization reaction sequence. The approach enables the one-pot facile construction of diverse compounds in moderate to excellent yields (47–82%). The 5-fluorouracil and 5-methyluracil moieties afford potentially bioactive molecules with drug-like properties. These scaffolds are currently being utilized in the screening deck of the European Lead Factory.

Diastereoselective One Pot Five-Component Reaction toward 4-(Tetrazole)-1,3-Oxazinanes

A diastereoselective one pot five-component reaction toward the synthesis of 4-(tetrazole)-1,3-oxazinanes has been reported. The sonication-accelerated, catalyst-free, simple, general and highly time efficient, Asinger-Ugi-tetrazole reaction was used for the synthesis of diverse 4-(tetrazole)-1,3-oxazinanes. The reaction exhibit excellent diastereoselectivity and broad substrate scope.

Highly Stereoselective Synthesis of a Compound Collection Based on the Bicyclic Scaffolds of Natural Products

Despite the great contribution of natural products in the history of successful drug discovery, there are significant limitations that persuade the pharmaceutical industry to evade natural products in drug discovery research. The extreme scarcity as well as structural complexity of natural products renders their practical synthetic access and further modifications extremely challenging. Although other alternative technologies, particularly combinatorial chemistry, were embraced by the pharmaceutical industry to get quick access to a large number of small molecules with simple frameworks that often lack three-dimensional complexity, hardly any success was achieved in the discovery of lead molecules. To acquire chemotypes beholding structural features of natural products, for instance high sp³ character, the synthesis of compound collections based on core-scaffolds of natural products presents a promising strategy. Here, we report a natural product inspired synthesis of six different chemotypes and their derivatives for drug discovery research. These bicyclic hetero- and carbocyclic scaffolds are highly novel, rich in sp³ features and with ideal physicochemical properties to display drug likeness. The functional groups on the scaffolds were exploited further to generate corresponding compound collections. Synthesis of two of these collections exemplified with ca. 350 compounds are each also presented. The whole compound library is being exposed to various biological screenings within the European Lead Factory consortium.

N-Hydroxyimide Ugi Reaction toward α-Hydrazino Amides

The Ugi four-component reaction (U-4CR) with N-hydroxyimides as a novel carboxylic acid isostere has been reported. This reaction provides straightforward access to α-hydrazino amides. A broad range of aldehydes, amines, isocyanides and N-hydroxyimides were employed to give products in moderate to high yields. This reaction displays N-N bond formation by cyclic imide migration in the Ugi reaction. Thus, N-hydroxyimide is added as a new acid component in the Ugi reaction and broadens the scaffold diversity.

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.