Still Unconquered: Enantioselective Passerini and Ugi Multicomponent Reactions

Photomediated One-Pot Three-Component Approach Enables the Formal Direct N-Acylation/Sulfonylation and α-C-H Functionalization of 1,2,3,4-Tetrahydroisoquinoline

N-Acyl/sulfonyl-α-functionalized 1,2,3,4-tetrahydroisoquinolines (THIQs) are significant structural motifs in organic synthesis and drug discovery. However, the one-pot approach enabling direct difunctionalization of THIQs remains challenging. Herein we report a photomediated one-pot three-component strategy to access N-acyl/sulfonyl-α-functionalized THIQs. This method features the use of oxygen (from air) as the green oxidant, high atom and step economy, and decent structural diversity. The synthetic applicability of the method was further demonstrated via the facile construction of valuable bioactive molecules. Mechanistic studies indicated that oxidation with singlet oxygen and the acceptor-less dehydrogenation were involved in the photoredox process.

De Novo Synthesis of α-Ketoamides via Pd/TBD Synergistic Catalysis

Precisely controlling the product selectivity of a reaction is an important objective in organic synthesis. α-Ketoamides are vital intermediates in chemical transformations and privileged motifs in numerous drugs, natural products, and biologically active molecules. The selective synthesis of α-ketoamides from feedstock chemicals in a safe and operationally simple manner under mild conditions is a long-standing catalysis challenge. Herein, an unprecedented TBD-switched Pd-catalyzed double isocyanide insertion reaction for assembling ketoamides in aqueous DMSO from (hetero)aryl halides and pseudohalides under mild conditions is reported. The effectiveness and utility of this protocol are demonstrated by its diverse substrate scope (93 examples), the ability to late-stage modify pharmaceuticals, scalability to large-scale synthesis, and the synthesis of pharmaceutically active molecules. Mechanistic studies indicate that TBD is a key ligand that modulates the Pd-catalyzed double isocyanide insertion process, thereby selectively providing the desired α-ketoamides in a unique manner. In addition, the imidoylpalladium(II) complex and α-ketoimine amide are successfully isolated and determined by X-ray analysis, confirming that they are probable intermediates in the catalytic pathway.

Saccharide branched cellulose with controllable molecular structure and excellent water retention ability

In this work, saccharide branched cellulose (saccharide b-Cel) was synthesized by combining reducing saccharides with cellulose molecules using Ugi four-component reaction (Ugi-4CR). First, the carboxyl groups required for Ugi-4CR are obtained by carboxymethylating cellulose molecules. Then, saccharide b-Cel with a controlled molecular structure is formed when the terminal aldehyde group of reducing saccharides combines with the carboxyl group and auxiliary functional group. The types of saccharides, the degree of substitution of carboxymethyl groups, and the degree of branching all affect the molecular structure of saccharide b-Cel. Through molecular structural regulation, the relationship between the branching structure and water retention ability of saccharide b-Cel was examined in detail. This work not only provides new insights into the synthesis of cellulose derivatives, but it also provides a template for the synthesis of other biomass derivatives.

Modular Assembly of 2-Aminoaniline Derivatives by Merging Hydroxylamine-Passerini and Hetero-Cope Rearrangement

A metal-free three-component protocol that combines a hydroxylamine-Passerini reaction and hetero-Cope rearrangement was realized, which enables the modular assembly of a wide range of structurally new and interesting 2-aminoanilines bearing an α-hydroxyamide substructure.

Cationic lipids from multi-component Passerini reaction for non-viral gene delivery: A structure-activity relationship study

Although many types of cationic lipids have been developed as efficient gene vectors, the construction of lipid molecules with simple procedures remains challenging. Passerini reaction, as a classic multicomponent reaction, could directly give the α-acyloxycarboxamide products with biodegradable ester and amide bonds. Herein, two series of novel cationic lipids with heterocyclic pyrrolidine and piperidine as headgroups were synthesized through Passerini reaction (P-series) and amide condensation (A-series), and relevant structure-activity relationships on their gene delivery capability was studied. It was found that although both of the two series of lipids could form lipid nanoparticles (LNPs) which could effectively condense DNA, the LNP derived from P-series lipids showed higher transfection efficiency, serum tolerance, cellular uptake, and lower cytotoxicity. Unlike the A-series LNPs, the P-series LNPs showed quite different structure-activity relationship, in which the relative site of the secondary amine had significant effect on the transfection performance. The othro-isomers of the P-series lipids had lower cytotoxicity, but poor transfection efficiency, which was probably due to their unstable nature. Taken together, this study not only validated the feasibility of Passerini reaction for the construction of cationic lipids for gene delivery, but also afforded some clues for the rational design of effective non-viral lipidic gene vectors.

Multicomponent Cyclizative 1,2-Rearrangement Enabled Enantioselective Construction of 2,2-Disubstituted Pyrrolinones

The 1,2-rearrangement reaction is one of the most important approaches to construct carbon-carbon bonds in organic synthesis. However, the development of catalytic asymmetric 1,2-rearrangements is still far from mature and often suffers from problems such as complex substrates, single product structure, and lack of synthetic application. Multicomponent reaction has been recognized as a robust tool for the synthesis of diverse and tunable products from readily available starting material. Conceptionally and practically, the development of multicomponent asymmetric 1,2-rearrangements is highly desirable. In this regard, we report herein a three-component benzilic acid-type rearrangement of 2,3-diketoesters, aromatic amines and aldehydes for the asymmetric construction of synthetically challenging pyrrolinones bearing aza-quaternary stereocenters. To the best of our knowledge, this reaction represents the first example of organocatalyzed multicomponent asymmetric 1,2-rearrangements.

Cyanation with isocyanides: recent advances and perspectives

Cyanation has attracted considerable attention in organic synthesis because nitriles are key structural motifs in numerous important dyes, agrochemicals, natural products and drug molecules. As the fourth generation of cyanating reagents, isocyanides occupy a prominent place in the synthesis of nitriles due to their favorable stability, easy operability and high reactivity. In recent years, three types of cyanation with isocyanides have been established: the cleavage of the C-NC bond of tertiary alkyl isocyanides (Type I), the rearrangement of aryl isocyanides with azides (Type II), and the reductive cyanation of ketones with α-acidic isocyanides (Type III). This review focuses on advances in cyanation with isocyanides with an emphasis on reaction scope, limitations and mechanisms, which could reveal their remarkable value and superiority for accessing various nitriles. In addition, the future development prospects of this specific field are also introduced. We believe that this feature article will serve as a comprehensive tool to navigate cyanation with isocyanides across the vast area of synthetic chemistry.

Crystal Clear: Decoding Isocyanide Intermolecular Interactions through Crystallography

The isocyanide group is the chameleon among the functional groups in organic chemistry. Unlike other multiatom functional groups, where the electrophilic and nucleophilic moieties are typically separated, isocyanides combine both functionalities in the terminal carbon. This unique feature can be rationalized using the frontier orbital concept and has significant implications for its intermolecular interactions and the reactivity of the functional group. In this study, we perform a Cambridge Crystallographic Database-supported analysis of isocyanide intramolecular interactions to investigate the intramolecular interactions of isocyanides in the solid state, excluding isocyanide-metal complexes. We discuss examples of different interaction classes, including the isocyanide as a hydrogen bond acceptor (RNC···HX), halogen bonding (RNC···X), and interactions involving the isocyanide and carbon atoms (RNC···C). The latter interaction serves as an intriguing illustration of a Bürgi-Dunitz trajectory and represents a crucial experimental detail in the well-known multicomponent reactions such as the Ugi- and Passerini-type mechanisms. Understanding the spectrum of intramolecular interactions that isocyanides can undergo holds significant implications in fields such as medicinal chemistry, materials science, and asymmetric catalysis.

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.

Photoredox radical cyclization reaction of o-vinylaryl isocyanides with acyl chlorides to access 2,4-disubstituted quinolines

We herein report an efficient photoredox radical cyclization reaction of o-vinylaryl isocyanides with acyl chlorides to access a wide range of 2,4-disubstituted quinolines. Preliminary mechanism experiment results suggested that this reaction was initiated by an acyl radical generated from acyl chlorides through a single-electron-transfer (SET) process. This transformation showed good substrate suitability and functional group compatibility at room temperature.

Enantioselective Multifunctionalization with Rh Carbynoids

Multifunctionalization from the interception of active intermediates is an attractive synthetic strategy for the efficient construction of complex molecular scaffolds in an atom and step economic fashion. However, the design of reactions involving metal carbynoids that exhibit carbene/carbocation behavior is currently limited, and developing catalyst-controlled highly enantioselective versions poses significant challenges. In this study, we present the first asymmetric trifunctionalization reactions with rhodium carbynoids. This reaction unveils the distinctive reactivity of the carbynoid precursor, enabling it to react with simultaneously two nucleophiles and one electrophile. This process involves the formation of two distinct carbene ylides with the alcohol/carbamate and the trapping of one ylide with the imine, resulting in the formation of three new bonds. Furthermore, this strategy allows for the divergent synthesis of a wide array of β-amino esters in high yields and exceptional enantioselectivity.

Three-Component Direct Phosphorylation of Aldehydes and Alkylation of Ketones: Synthesis of γ-Ketophosphine Oxides under Acidic Conditions

An effective and economical acid-promoted three-component reaction for the construction of C-P and C-C bonds for the synthesis of γ-ketophosphine oxides with water as the only byproduct was developed. Detailed mechanistic experiments confirmed that the reaction proceeds by phospha-aldol elimination, in which a benzylic carbocation is generated from the phosphorylation of aldehydes, which then reacts with ketone enolates under acidic conditions.

Rapid Access to Fused Tetracyclic N-Heterocycles via Amino-to-Alkyl 1,5-Palladium Migration Coupled with Intramolecular C(sp3)-C(sp2) Coupling

An unprecedented route for the preparation of fused tetracyclic N-heterocycles is presented through the palladium-catalyzed cyclization of isocyanides with alkyne-tethered aryl iodides. In this transformation, a novel amino-to-alkyl 1,5-palladium migration/intramolecular C(sp3)-C(sp2) coupling sequence was observed first. More importantly, isocyanide exhibited three roles, serving simultaneously as a C1 synthon, a C1N1 synthon, and the donor of C(sp3) for C(sp3)-C(sp2) coupling, and the reaction was the sole successful example that achieved C(sp3)-H activation of isocyanide.

Accessing indole-isoindole derivatives via palladium-catalyzed [3+2] cyclization of isocyanides with alkynyl imines

A facile protocol for the preparation of indole-isoindole derivatives was developed and proceeds via a palladium-catalyzed [3+2] cyclization of isocyanides with alkynyl imines. In this transformation, the palladium catalyst has a triple role, serving simultaneously as a π acid, a transition-metal catalyst and a hydride ion donor, thus enabling the dual function of isocyanide both as a C1 synthon for cyanation and a C1N1 synthon for imidoylation. Significantly, the reaction is the sole successful example for accessing indole-isoindole derivatives, and will open up new avenues to assemble unique N-heterocycle frameworks. Furthermore, the synthetic value of this protocol is demonstrated in the late-stage modification of physiologically active molecules and in the construction of aggregation-induced emission compounds.

Construction of Covalent Organic Frameworks via Multicomponent Reactions

Multicomponent reactions (MCRs) combine at least three reactants to afford the desired product in a highly atom-economic way and are therefore viewed as efficient one-pot combinatorial synthesis tools allowing one to significantly boost molecular complexity and diversity. Nowadays, MCRs are no longer confined to organic synthesis and have found applications in materials chemistry. In particular, MCRs can be used to prepare covalent organic frameworks (COFs), which are crystalline porous materials assembled from organic monomers and exhibit a broad range of properties and applications. This synthetic approach retains the advantages of small-molecule MCRs, not only strengthening the skeletal robustness of COFs, but also providing additional driving forces for their crystallization, and has been used to prepare a series of robust COFs with diverse applications. The present perspective article provides the general background for MCRs, discusses the types of MCRs employed for COF synthesis to date, and addresses the related critical challenges and future perspectives to inspire the MCR-based design of new robust COFs and promote further progress in this emerging field.

Sequential Cu(II)-Catalyzed Multicomponent C-N Coupling, Nucleophilic Addition, and Cyclization Cascade: A Diastereoselective Approach to Carboxamide-Embedded Hexahydrobenzofuran Core

Cascade or domino reactions serve as a powerful technique for the synthesis of complex organic scaffolds in one pot. Herein, a Cu(II)-catalyzed and silica gel-assisted multicomponent reaction (MCR) between bromoalkyne-tethered cyclohexadienones, amides, and water for the construction of hexahydrobenzofuran-3-carboxamide is developed. The reaction proceeds via a C-N coupling reaction followed by hydrative cyclization of ynamide intermediates. Notably, good to excellent diastereoselectivity is complementary of this reaction.

Recent Advances in the Electrochemical Functionalization of Isocyanides

Isocyanides are well-known as efficient CO surrogates and C1 synthons in modern organic synthesis. Although tremendous efforts have been devoted to fully exploiting the reactivity of isocyanides, these transformations are primarily limited by their utilization of stoichiometric toxic chemical oxidants. With the recent resurgence of organic electrochemistry, which has considerably laid dormant over the past several decades, electrolysis has been identified as a green and powerful tool to enrich structural diversity by solely utilizing electric current as clean and inherently safe redox equivalents of stoichiometric chemical oxidants. In this regard, the unique reactivity of isocyanides has been studied in numerous electrochemical transformations. This review comprehensively highlights the most relevant progress in electrochemical strategies towards the functionalization of isocyanides up until June of 2022, with a focus on reaction outcomes and mechanisms.

Coupling of Thiazole-2-Amines with Isocyanide Ligands in bis-(Isocyanide) Platinum Complex: A New Type of Reactivity

The treatment of cis-[PtCl2(XylNC)2] with thiazol-2-amines in a 2:1 ratio leads to a regioisomeric mixture of two binuclear complexes. These regioisomers are products of kinetic and thermodynamic control capable of regioisomerization. When the same reaction is carried out with a 5-fold excess of thiazol-2-amine, the nucleophile is able to react with the in situ-formed binuclear platinum(II) complexes, yielding a new type of bis-carbene platinum species. All new isolated compounds were characterized by 1H, 13C{1H}, and 195Pt{1H} NMR spectroscopy, high-resolution ESI-MS, and single-crystal X-ray diffraction.

An enantioselective four-component reaction via assembling two reaction intermediates

A reaction intermediate is a key molecular entity that has been used in explaining how starting materials converts into the final products in the reaction, and it is usually unstable, highly reactive, and short-lived. Extensive efforts have been devoted in identifying and characterizing such species via advanced physico-chemical analytical techniques. As an appealing alternative, trapping experiments are powerful tools in this field. This trapping strategy opens an opportunity to discover multicomponent reactions. In this work, we report various highly diastereoselective and enantioselective four-component reactions (containing alcohols, diazoesters, enamines/indoles and aldehydes) which involve the coupling of in situ generated intermediates (iminium and enol). The reaction conditions presented herein to produce over 100 examples of four-component reaction products proceed under mild reaction conditions and show high functional group tolerance to a broad range of substrates. Based on experimental and computational analyses, a plausible mechanism of this multicomponent reaction is proposed.

Enantioselective Ugi and Ugi-azide reactions catalyzed by anionic stereogenic-at-cobalt(III) complexes

Ugi reactions and related variations are proven to be atom and step-economic strategies for construction of highly valuable peptide-like skeletons and nitrogenous heterocycles. The development of structurally diverse range of novel catalytic systems and the discovery of new approaches to accommodate a broader scope of terminating reagents for asymmetric Ugi four-component reaction is still in high demand. Here, we report a strategy that enables enantioselective Ugi four-component and Ugi-azide reactions employing anionic stereogenic-at-cobalt(III) complexes as catalysts. The key nitrilium intermediates, generated through the nucleophilic addition of isocyanides to the chiral ion-pair which consists of stereogenic-at-cobalt(III) complexes counteranion and a protonated iminium, are trapped by either carboxylic acids or in situ-generated hydrazoic acid, delivering α-acylamino amides and α-aminotetrazoles in good to excellent enantioselectivities (up to 99:1 e.r.).

Cascade reaction of o-enoyl arylisocyanide and o-hydroxy aromatic aldimine: diastereoselective access to a polycyclic spirobenzoxazine chromeno[4,3-b]pyrrole derivative

A series of structurally unusual spirobenzoxazine chromeno[4,3-b]pyrrole derivatives have been efficiently constructed in a single operation from readily available starting materials. This domino transformation forms successively three new rings and provides a fast and economic strategy with excellent diastereoselectivity.

Copper-Catalyzed One-Step Formation of Four C-N Bonds toward Polyfunctionalized Triazoles via Multicomponent Reaction

A novel four-component reaction of alkynes, amines, azides, and 2H-azirines has been developed for the first time by the efficient formation of four C-N bonds in one step under mild conditions, rapidly preparing polyfunctionalized triazoles with molecular diversity involving three different intermediates of copper-acetylide, copper-allenylidene, and copper-vinyl nitrene. Propargylic ester is disclosed as a "three-in-one" building block possessing triplicate cycloaddition and nucleophilic and electrophilic properties, which could enable such a four-component transformation by high yields, broad substrate scope, and functionalization.

Solvent Dependent Competitive Mechanisms for the Ugi Multicomponent Reaction: A Joint Theoretical and Experimental Study in the α-Acyl Aminocarboxamides vs α-Amino Amidines Formation

A synthetic protocol for the preparation of α-acyl aminocarboxamides and α-amino amidines is proposed. The selectivity toward each of these two possible products was tuned by simple modifications of the reaction conditions. A broad scope is presented, allowing access to the desired products in up to 87% (Ugi adduct) and 93% (α-amino amidine). Theoretical calculations were carried out, and the analysis led to the proposal of a new mechanistic pathway for the Ugi reaction, in which methanol acts not only as the solvent but also as a reagent. High-resolution (tandem) mass spectrometry experiments allowed the detection and characterization of the key intermediate associated with this new and alternative reaction pathway, thus supporting the theoretical proposal.

Innovations and Inventions: Why Was the Ugi Reaction Discovered Only 37 Years after the Passerini Reaction?

This year represents the 100th anniversary of the discovery of the Passerini three-component reaction. The related Ugi four-compound reaction was discovered 37 years after the Passerini reaction. Undoubtedly, both reactions are very important multicomponent reactions but the Ugi reactions outperform the Passerini reactions in terms of combinatorial space according to the equation x^y [x is the number of building blocks per component, and y is the order of the multicomponent reaction (for Passerini, y = 3; for Ugi, y = 4)]. In this work, a historical but contemporary perspective of the discoveries and innovations of the two reactions is given. From a bird's eye view and in a more general sense, the discovery of novel reactions is discussed and how it relates to inventions and innovations.

Biosynthesis of Isonitrile- and Alkyne-Containing Natural Products

Natural products are a diverse class of biologically produced compounds that participate in fundamental biological processes such as cell signaling, nutrient acquisition, and interference competition. Unique triple-bond functionalities like isonitriles and alkynes often drive bioactivity and may serve as indicators of novel chemical logic and enzymatic machinery. Yet, the biosynthetic underpinnings of these groups remain only partially understood, constraining the opportunity to rationally engineer biomolecules with these functionalities for applications in pharmaceuticals, bioorthogonal chemistry, and other value-added chemical processes. Here, we focus our review on characterized biosynthetic pathways for isonitrile and alkyne functionalities, their bioorthogonal transformations, and prospects for engineering their biosynthetic machinery for biotechnological applications.

Ionic Reactivity of 2-Isocyanoaryl Thioethers: Access to 2-Halo and 2-Aminobenzothia/Selenazoles

An ionic cascade insertion/cyclization reaction of thia-/selena-functionalized arylisocyanides has been successfully developed for the efficient and practical synthesis of 2-halobenzothiazole/benzoselenazole derivatives. This synthetic protocol, incorporating a halogen atom when forming the five-membered ring of benzothia/selenazoles, is different from the existing ones, where halogenation of the preformed benzothia/selenazole precursors happens. Additionally, a facile access to 2-aminobenzothiazoles is also achieved by the one-pot cascade reaction of 2-isocyanoaryl thioethers, iodine, and amines.

Molecular insights into chirality transfer from double axially chiral phosphoric acid in a synergistic enantioselective intramolecular amination

In the most general practice of asymmetric catalysis, a chiral catalyst, typically bearing a center or an axis of chirality, is employed as the chiral source for imparting enantiocontrol over the developing product. Given the current interest toward optically pure compounds, various forms of chiral induction enabled by diverse chiral sources as well as the use of multiple catalysts under one-pot conditions have been in focus. In one such promising development, an achiral N-sulfonamide protected 1,6-amino allyl alcohol (NaphSO₂NHCH₂C(Ph)₂CH₂CH Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> CHCH₂OH) was subjected to Tsuji–Trost activation and an intramolecular amination to form important chiral pyrrolidine frameworks. A dual catalytic system comprising Pd(PPh₃)₄ and DAPCy (β-cyclohexyl substituted double axially chiral phosphoric acid derived from two homocoupled BINOL backbones with a dynamic central chiral axis) under mild conditions was reported to offer quantitative conversion with an ee of 95%. Here, we provide molecular insights into the origin of chiral induction by DAPCy, as obtained through a comprehensive density functional theory (SMD_(toluene)/B3LYP-D3/6-31G**,Pd(SDD)) investigation. Two key steps in the mechanism are identified to involve a cooperative mode of activation of the Pd-bound allyl alcohol in the form of a Pd-π-allyl moiety at one end of the substrate, followed by an intramolecular nucleophilic addition of N-sulfonamide from the other end to yield a pyrrolidine derivative bearing an α-vinyl stereogenic center. (S,R,S)-DAPCy is found to steer the dehydroxylation to yield a Pd-π-allyl intermediate with a suitably poised si prochiral face for the nucleophilic addition. In the enantiocontrolled (as well as the turn-over determining step) nucleophilic addition, the chiral catalyst is identified to serve as a chiral phosphate counterion. The chiral induction is facilitated by a series of N–H⋯O, C–H⋯O, C–H⋯π, lone pair (lp)⋯π, O–H⋯O, O–H⋯π, and π⋯π noncovalent interactions, which is noted as more effective in the lower energy C–N bond formation transition state through the si prochiral face of the Pd-π-allyl moiety. These insights into the novel dynamic axially double chiral catalyst could be valuable toward exploiting such modes of stereoinduction.

The origin of enantiocontrol in an intramolecular amination involving Pd(PPh₃)₄ and a double axially chiral phosphoric acid (DAPCy) dual catalytic system is traced to a more effective series of noncovalent interactions in the lower energy C–N bond formation transition state.

Catalytic Metal-Enabled Romance of Isocyanides for Use as “C1N1” Synthons in Cyclization: Beyond Radical Chemistry

Cyclizative reactions have attracted considerable attentions in organic synthesis with regard to the high atom economy and synthetic efficiency towards cyclic architectures. Especially, isocyanide-based cyclizations have proven to be a...

An overview of the applications of chiral phosphoric acid organocatalysts in enantioselective additions to CO and CN bonds

Since 2004, chiral phosphoric acids (CPAs) have emerged as highyl efficient organocatalysts, providing excellent results in a wide reaction scope. In this review, the applications of CPA for enantioselective additions to CO and CN bonds are covered.

Asymmetric synthesis of polycyclic spiroindolines via the Dy-catalyzed cascade reaction of 3-(2-isocyanoethyl)indoles with aziridines

An asymmetric cascade reaction catalyzed by a chiral N,N′-dioxide–Dy(iii) complex was realized to construct the valuable [6,5,5,6] tetracyclic spiroindolines with good yields and enantioselectivities by a concise and one-step protocol.

The regioselectivity of the sulfonylation of tetrazoles: a theoretical view

DFT calculations were performed to reveal the regioselectivity for the sulfonylation of tetrazoles.

An Olefin-based Multi-component Reaction to 1,2-Azaborolidine Derivatives

Reaction of the borane FmesBH2·SMe2 [Fmes: 2,4,6-tris(trifluoro-methyl)phenyl] with two molar equivs of a small series of 1-alkenes followed by treatment with two molar equivalents of the bulky isonitrile CN-Xyl (Xyl:...

Three-Component Reaction to 1,4,2-Diazaborole-Type Heteroarene Systems

The borane FmesBH₂ reacts in a three-component reaction with an isonitrile and a small series of organonitriles to give rare examples of the class of dihydro-1,4,2-diazaborole derivatives. In a related way, annulated BN-indolizine derivatives became conveniently available, as were dihydro-1,4,2-oxaza- or thiazaborole derivatives. The nucleophilic framework of a dihydro-1,4,2-diazaborole example allowed for an uncatalyzed acylation reaction. It also served as a 1,3-dipolar reagent and underwent a [3+2] cycloaddition/[4+2] cycloreversion sequence when treated with methyl propiolate to give the respective pyrrole product. The [3+2] cycloaddition product of a dihydro-1,4,2-diazaborole derivative with N-phenylmaleimide was isolated and its heterobicyclo[2.2.1]heptane derived structure characterized by X-ray diffraction.

Green Chemistry in the Synthesis of Pharmaceuticals

The principles of green chemistry (GC) can be comprehensively implemented in green synthesis of pharmaceuticals by choosing no solvents or green solvents (preferably water), alternative reaction media, and consideration of one-pot synthesis, multicomponent reactions (MCRs), continuous processing, and process intensification approaches for atom economy and final waste reduction. The GC's execution in green synthesis can be performed using a holistic design of the active pharmaceutical ingredient's (API) life cycle, minimizing hazards and pollution, and capitalizing the resource efficiency in the synthesis technique. Thus, the presented review accounts for the comprehensive exploration of GC's principles and metrics, an appropriate implication of those ideas in each step of the reaction schemes, from raw material to an intermediate to the final product's synthesis, and the final execution of the synthesis into scalable industry-based production. For real-life examples, we have discussed the synthesis of a series of established generic pharmaceuticals, starting with the raw materials, and the intermediates of the corresponding pharmaceuticals. Researchers and industries have thoughtfully instigated a green synthesis process to control the atom economy and waste reduction to protect the environment. We have extensively discussed significant reactions relevant for green synthesis, one-pot cascade synthesis, MCRs, continuous processing, and process intensification, which may contribute to the future of green and sustainable synthesis of APIs.

Ternary Catalysis Enabled Three-Component Asymmetric Allylic Alkylation as a Concise Track to Chiral α,α-Disubstituted Ketones

Multicomponent reactions that involve interception of onium ylides through Aldol, Mannich, and Michael addition with corresponding bench-stable acceptors have demonstrated broad applications in synthetic chemistry. However, because of the high reactivity and transient survival of these in situ generated intermediates, the substitution-type interception process, especially the asymmetric catalytic version, remains hitherto unknown. Herein, a three-component asymmetric allylation of α-diazo carbonyl compounds with alcohols and allyl carbonates is disclosed by employing a ternary cooperative catalysis of achiral Pd-complex, Rh₂(OAc)₄, and chiral phosphoric acid CPA. This method represents the first example of three-component asymmetric allylic alkylation through an S_N1-type trapping process, which involves a convergent assembly of two active intermediates, Pd-allyl species, and enol derived from onium ylides, providing an expeditious access to chiral α,α-disubstituted ketones in good to high yields with high to excellent enantioselectivity. Combined experimental and computational studies have shed light on the mechanism of this novel three-component reaction, including the critical role of Xantphos ligand and the origin of enantioselectivity.

The 100 facets of the Passerini reaction

This perspective aims at celebrating the 100th anniversary of the discovery of the Passerini three component reaction. After being nearly neglected for many years, now this reaction has become quite popular, thanks to the achievements of the last 30 years, which have revealed several chances of exploitation in organic synthesis. Though not being comprehensive, this review means to show the various ways that have been used in order to expand the utility of the Passerini reaction. Post-MCR transformations to give heterocycles or peptidomimetics, variants through single component replacement, stereochemical issues, and applications in total syntheses will be especially covered.