A palladium-catalysed multicomponent coupling approach to conjugated poly(1,3-dipoles) and polyheterocycles

Ferrocene-Based Antioxidant Self-Healing Hydrogel via the Biginelli Reaction for Wound Healing

The development of antioxidant wound dressings to remove excessive free radicals around wounds is essential for wound healing. In this study, we developed an efficient strategy to prepare antioxidant self-healing hydrogels as wound dressings by combining multicomponent reactions (MCRs) and postpolymerization modification. A polymer containing ferrocene and phenylboronic acid groups was developed via the Biginelli reaction, followed by efficient modification. This polymer is antioxidant due to its ferrocene moieties and can rapidly cross-link poly(vinyl alcohol) to realize an antioxidant self-healing hydrogel through dynamic borate ester linkages. This hydrogel has low cytotoxicity and is biocompatible. In in vivo experiments, this hydrogel is superior to existing clinical dressings in promoting wound healing. This study demonstrates the value of the Biginelli reaction in exploring biomaterials, potentially offering insights into the design of other multifunctional polymers and related materials using different MCRs.

Access to 2,4-Disubstituted Pyrrole-Based Polymer with Long-Wavelength and Stimuli-Responsive Properties via Copper-Catalyzed [3+2] Polycycloaddition

Pyrrole-based polymers (PBPs), a type of fascinating functional polymers, play a crucial role in materials science. However, efficient synthetic strategies of PBPs with diverse structures are mainly focused on conjugated polypyrroles and still remain challenging. Herein, an atom and step economy protocol is described to access various 2,4-disubstituted PBPs by in situ formation of pyrrole core structure via copper-catalyzed [3+2] polycycloaddition of dialkynones and diisocyanoacetates. A series of PBPs is prepared with high molecular weight (Mw up to 18 200 Da) and moderate to good yield (up to 87%), which possesses a fluorescent emission located in the green to yellow light region. Blending the PBPs with polyvinyl alcohol, the stretchable composite films exhibit a significant strengthening of the mechanical properties (tensile stress up to 59 MPa, elongation at break >400%) and an unprecedented stress-responsive luminescence enhancement that over fourfold fluorescent emission intensity is maintained upon stretching up to 100%. On the basis of computational studies, the unique photophysical and mechanical properties are attributed to the substitution of carbonyl chromophores on the pyrrole unit.

A Photoactivatable Luminescent Motif through Ring-Flipping Isomerization for Multiple Photopatterning

Photoactivatable luminescent materials have garnered enormous attention in the field of intelligent responsive materials, yet their design and applications remain challenging due to the limited variety of photoactivatable motifs. In the work described herein, we discovered a new photoactivatable luminescent motif that underwent ring-flipping isomerization under UV irradiation. The emission of this motif exhibited a rapid transformation from dark yellow to bright green, accompanied by a significant enhancement of quantum yield from 1.9% to 34.2%. Experimental and theoretical studies revealed that the effective intramolecular motion (EIM) was crucial to the distinct luminescence performance between two isomers. In addition, polymers containing this motif were achieved through a one-pot alkyne polymerization, exhibiting both photofluorochromic and photo-cross-linking properties. Furthermore, multiple types of photopatterning, including luminescent encryption, fluorescent grayscale imaging, and high-resolution photolithographic patterns, were realized. This work developed a new photoactivatable luminescent motif and demonstrated its potential applications in both small molecules and macromolecules, which will help in the future design of photoactivatable luminescent materials.

Superhydrophobic Coatings Composed of Multifunctional Polymers Synthesized Using Successive Modification of Dihydropyrimidin-2(1H)-thione

Polymer synthesis via multicomponent reactions (MCRs) has opened avenues in polymer chemistry and led to the development of various types of functional polymers. Herein, we developed a strategy to prepare multifunctional polymers via the successive modification of dihydropyrimidin-2(1H)-thione (DHPMT), which can be generated by the tricomponent Biginelli reaction. Four hydrophobic polymers were efficiently prepared by using DHPMT derivatives. These polymers can be dip-coated onto the oxidized copper mesh to obtain superhydrophobic meshes because of the strong attractive forces between the DHPMT derivatives and Cu(II). The optimized mesh has self-cleaning properties and outstanding stability in various liquid environments; it has also been successfully applied for oil/water separation with high separation efficiency and good durability. These results demonstrate that successive modification of DHPMT is a promising method for fabricating multifunctional polymers, which may have applications in polymer chemistry and materials science.

Poly(vinyl alcohol) Modified via the Hantzsch Reaction for Biosafe Antioxidant Self-Healing Hydrogel

Efficient routes for the preparation of functional self-healing hydrogels from functional polymers are needed. In this study, we developed a strategy to effectively produce a vanillin-modified poly(vinyl alcohol) (PVA-vanillin) through the Hantzsch reaction. This polymer was cross-linked with a phenylboronic acid-containing polymer (PB) that was also prepared using the Hantzsch reaction to fabricate a hydrogel through borate ester linkages under mild conditions (25 °C, pH ∼ 7.4). This hydrogel had excellent antioxidant abilities due to the 1,4-dihydropyridine (DHP) rings and the vanillin moieties in the hydrogel structures; it was also self-healable and injectable owing to the dynamic borate ester linkages. Furthermore, the antioxidant self-healing hydrogel had low cytotoxicity and exhibited favorable safety in animal experiments, indicating its potential as a safe implantable cell or drug carrier. This study developed a method for preparing functional polymers and related self-healing hydrogels in a facile manner; it demonstrated the value of the Hantzsch reaction in exploiting antioxidant self-healing hydrogels for biomedical applications, which may provide insight into the design of other functional self-healing hydrogels through different multicomponent reactions.

Advances in the application of named reactions in polymer synthesis

With the development of polymer science, more and more named reactions have been applied to synthesizing polymers. Introducing new reactions into polymer synthesis is undoubtedly an excellent expansion for monomer and polymer libraries. In this review, the named reactions employed in polymer-chain synthesis were divided into seven types: electrophilic reactions, nucleophilic reactions, transition metal-mediated cross-coupling reactions, free radical reactions, pericyclic reactions, multi-component reactions and rearrangement reactions. The discussion was mainly focused on the progress in the utilization of these named reactions in polymer synthesis, which could be a valuable reference for researchers in the polymer field.

Stepping Further from Coupling Tools: Development of Functional Polymers via the Biginelli Reaction

Multicomponent reactions (MCRs) have been used to prepare polymers with appealing functions. The Biginelli reaction, one of the oldest and most famous MCRs, has sparked new scientific discoveries in polymer chemistry since 2013. Recent years have seen the Biginelli reaction stepping further from simple coupling tools; for example, the functions of the Biginelli product 3,4-dihydropyrimidin-2(1H)-(thi)ones (DHPM(T)) have been gradually exploited to develop new functional polymers. In this mini-review, we mainly summarize the recent progress of using the Biginelli reaction to identify polymers for biomedical applications. These polymers have been documented as antioxidants, anticancer agents, and bio-imaging probes. Moreover, we also provide a brief introduction to some emerging applications of the Biginelli reaction in materials and polymer science. Finally, we present our perspectives for the further development of the Biginelli reaction in polymer chemistry.

Magnetic Self-Healing Hydrogel from Difunctional Polymers Prepared via the Kabachnik-Fields Reaction

The development of high quality magnetic self-healing hydrogels containing well-dispersed magnetic nanoparticle has been a challenging procedure due to unavailable methods of facilely introducing groups that can efficiently stabilize these magnetic nanoparticles in the self-healing hydrogels. In this research, a polymer containing both phenylboronic acid (PBA) and phosphonic acid (PA) groups has been developed by the Kabachnik-Fields (KF) reaction. This polymer well disperses iron oxide nanoparticles (IONPs) through the strong interactions between the PA groups and the surface of the IONPs; thus, this polymer effectively mixed IONPs and poly(vinyl alcohol) (PVA) to form a hydrogel containing well-dispersed IONPs. The resulting hydrogel is self-healing, owing to the dynamic borate ester linkages. Moreover, the presence of the IONPs endowed the hydrogel with magnetic properties, also making it heat-responsive in an alternating magnetic field and expanding its application as a contrast agent for magnetic resonance imaging. The magnetic self-healing hydrogel showed excellent biosafety properties in animal experiments, suggesting its potential as an injectable implant material for biological and medical applications. This research exploits a biocompatible magnetic self-healing hydrogel with well-dispersed IONPs, demonstrating the value of the KF reaction in the development of functional polymers and smart materials, which might prompt a broad study of multicomponent reactions in interdisciplinary fields.

Introducing the aza-Michael addition reaction between acrylate and dihydropyrimidin-2(1H)-thione into polymer chemistry

The aza-Michael addition reaction between dihydropyrimidin-2(1H)-thione and acrylate has been used to fabricate new polymers through different synthesis routes.

De Novo Design of Entropy-Driven Polymers Resistant to Bacterial Attachment via Multicomponent Reactions

Nonbactericidal polymers that prevent bacterial attachment are important for public health, environmental protection, and avoiding the generation of superbugs. Here, inspired by the physical bactericidal process of carbon nanotubes and graphene derivatives, we develop nonbactericidal polymers resistant to bacterial attachment by using multicomponent reactions (MCRs) to introduce molecular "needles" (rigid aliphatic chains) and molecular "razors" (multicomponent structures) into polymer side chains. Computer simulation reveals the occurrence of spontaneous entropy-driven interactions between the bacterial bilayers and the "needles" and "razors" in polymer structures and provides guidance for the optimization of this type of polymers for enhanced resistibility to bacterial attachment. The blending of the optimized polymer with commercially available polyurethane produces a film with remarkably superior stability of the resistance to bacterial adhesion after wear compared with that of commercial mobile phone shells made by the Sharklet technology. This proof-of-concept study explores entropy-driven polymers resistant to bacterial attachment via a combination of MCRs, computer simulation, and polymer chemistry, paving the way for the de novo design of nonbactericidal polymers to prevent bacterial contamination.

Room-Temperature Metal-Free Multicomponent Polymerizations of Elemental Selenium toward Stable Alicyclic Poly(oxaselenolane)s with High Refractive Index

Selenium-containing polymers are a group of fascinating functional polymers with unique structures, properties, and applications, which have been developed recently but only with limited examples. The challenges of developing selenium-containing polymers with structural and functional diversity include the lack of economic and safe monomers, lack of efficient and convenient synthetic approaches, and poor stability of selenium-involving covalent bonds. In this work, room-temperature metal-free multicomponent polymerizations (MCPs) of elemental selenium, diisocyanides, and dipropargyl alcohols were developed, and polymers with a selenium-containing aliphatic heterocycle, 1,3-oxaselenolane, were synthesized through these MCPs directly from elemental selenium. The alicyclic poly(oxaselenolane)s enjoyed high yields (up to 93%), high molecular weights (up to 15 600 g/mol), high thermal and chemical stability, good solubility and processability. With the structural design of the poly(oxaselenolane)s and their high selenium contents of up to 33.7 wt %, the refractive indices of their spin-coated thin films could reach 1.8026 at 633 nm and maintain 1.7770 at 1700 nm. It is anticipated that these efficient, convenient, mild, and economic multicomponent polymerizations of elemental selenium can promote the selenium-related polymer chemistry and accelerate the exploration of diversified selenium-containing functional polymer materials.

Click and Bio-Orthogonal Reactions with Mesoionic Compounds

Click and bio-orthogonal reactions are dominated by cycloaddition reactions in general and 1,3-dipolar cycloadditions in particular. Among the dipoles routinely used for click chemistry, azides, nitrones, isonitriles, and nitrile oxides are the most popular. This review is focused on the emerging click chemistry that uses mesoionic compounds as dipole partners. Mesoionics are a very old family of molecules, but their use as reactants for click and bio-orthogonal chemistry is quite recent. The facility to derivatize these dipoles and to tune their reactivity toward cycloaddition reactions makes mesoionics an attractive opportunity for future click chemistry development. In addition, some compounds from this family are able to undergo click-and-release reactions, finding interesting applications in cells, as well as in animals. This review covers the synthetic access to main mesoionics, their reaction with dipolarophiles, and recent applications in chemical biology and heterocycle synthesis.

Palladium catalyzed synthesis of indolizines via the carbonylative coupling of bromopyridines, imines and alkynes

We report herein the development of a palladium-catalyzed, multicomponent synthesis of indolizines. The reaction proceeds via the carbonylative formation of a high energy, mesoionic pyridine-based 1,3-dipole, which can undergo spontaneous cycloaddition with alkynes. Overall, this provides a route to prepare indolizines in a modular fashion from combinations of commercially available or easily generated reagents: 2-bromopyridines, imines and alkynes.

A palladium catalyzed, multicomponent synthesis of indolizines is described via the carbon monoxide driven generation of reactive, pyridine-based 1,3-dipoles.

Multicomponent Polymerization for π-Conjugated Polymers

Structurally complex π-conjugated polymers hold great promise as key components in sensor and electronic devices; however, their syntheses have not been a trivial task. From a synthetic efficiency perspective, it would be more attractive to access these materials using convenient and efficient methods from simple building blocks. One such synthetic tool, multicomponent polymerization, can accommodate modularity and provide highly efficient syntheses. This feature article outlines several multicomponent polymerization strategies for the synthesis of various π-conjugated polymers, which are classified based upon how the monomers are aligned during polymerization. Additionally, the challenges and outlooks of this field are highlighted and discussed.

Catalyst-Free Four-Component Polymerization of Propiolic Acids, Benzylamines, Organoboronic Acids, and Formaldehyde toward Functional Poly(propargylamine)s

Multicomponent polymerizations (MCPs) are a group of fascinating polymer synthesis approaches that are developed rapidly in the recent decade. As a popular alkyne-based MCP, the A³ -polycouplings of alkynes, aldehydes, and amines are developed for the synthesis of poly(propargylamine)s under the catalysis of metal catalysts. In this work, through the design of carboxylic acid group-activated alkyne monomers, a catalyst-free, four-component polymerization of propiolic acids, benzylamines, organoboronic acids, and formaldehyde is reported under mild condition at 45 °C in dichloroethane. This four-component polymerization is applicable to different monomer structures, which can afford seven poly(propargylamine)s with up to 94% yields and molecular weights of up to 13 900 g mol^-1 . Moreover, the poly(propargylamine)s demonstrate good solubility and processibility, high thermal stability and light refractivity, unique photophysical property, and so on. The simple monomers, mild condition, low cost, high efficiency, and procedure simplicity of this catalyst-free four-component polymerization demonstrates an elegant example of functional polymer synthesis.

Palladium-catalyzed multicomponent reactions: an overview

This first review on this topic focuses on the developments in the chemistry of Pd-catalyzed multi-component reactions (MCRs). MCRs are generally atom economic, ideal and eco-friendly reactions, and often the final products are generated almost without any by-products. In this review, the developments in Pd-catalyzed MCRs are categorized based on the products formed such as acyclic compounds, carbocyclic compounds, heterocyclic compounds and miscellaneous compounds. MCRs have great applications in various fields like medicinal chemistry, combinatorial synthesis, heterocyclic chemistry etc. and this review covers the literature up to 2019.

Direct Construction of Acid-Responsive Poly(indolone)s through Multicomponent Tandem Polymerizations

Multicomponent polymerizations (MCPs) as a burgeoning field in polymer chemistry has proved to be a powerful and popular tool for the synthesis of functional polymer materials with diverse and complex structures. To explore the general applicability of MCPs and enrich the product structures of MCPs, multicomponent tandem polymerizations (MCTPs) with great synthetic simplicity and efficiency were pursued. In this work, MCTPs of N-(2-iodophenyl)-3-phenyl-N-tosylpropiolamide, aromatic terminal alkynes, and diamines were explored through combining Sonogashira coupling and Michael addition reaction in a one-pot procedure. The MCTPs could proceed efficiently and conveniently under mild conditions with Pd(PPh₃)₂Cl₂, CuI, and i-Pr₂NEt, affording 12 poly(indolone)s with unique structures and high M_ws (up to 30400 g/mol) in high yields (up to 97%). The poly(indolone)s possess a unique acid-triggered fluorescence "turn-on" response which could realize specific detection of CF₃SO₃H from other inorganic and organic acids through a rapid acid-catalyzed reaction from enamine to ketone.

PEG-conjugated pyrrole-based polymers: one-pot multicomponent synthesis and self-assembly into soft nanoparticles for drug delivery

A simple one-pot methodology provides easy access to amphiphilic PEG–pyrrole backbone polymers, which self-assemble into soft nanoparticles enabling efficient drug loading/sustained release and can be detected inside cells.

Palladium-catalyzed carbene coupling of N-tosylhydrazones and arylbromides to synthesize cross-conjugated polymers

Palladium-catalyzed cross-coupling reactions of N-tosylhydrazones and arylbromides have been applied for the first time in the synthesis of cross-conjugated polymers, namely poly(arylene-1,1-vinylidene)s (iso-PAVs).

Functional Poly(dihalopentadiene)s: Stereoselective Synthesis, Aggregation-Enhanced Emission and Sensitive Detection of Explosives

The development of polymeric materials with novel structures and unique properties and functionalities is of both academic and industrial significance. In this work, functional poly(dihalopentadiene)s were synthesized by boron trihalide-mediated multicomponent polymerization routes in a stereoselective manner. The polymerizations of tetraphenylethylene-containing diyne, BX₃ (X = Cl, Br) and p-tolualdehyde proceed smoothly in dichloromethane under mild conditions to afford high molecular weight poly(dihalopentadiene)s with a predominant (Z,Z)-configuration in moderate to good yields. The reaction conditions and the boron trihalide used were found to have great effects on the stereochemistry of the resulting polymer structures. The obtained poly(1,5-dihalo-(Z,Z)-1,4-pentadiene)s possess high thermal stability and good film-forming ability. Their thin films show high refractive index of 1.9007⁻1.6462 in a wide wavelength region of 380⁻890 nm with low optical dispersion. The polymers are weakly emissive in dilute solutions but become highly emissive upon aggregated, demonstrating a unique phenomenon of aggregation-enhanced emission. Their nanoaggregates in aqueous media can serve as sensitive fluorescent chemosensors for the detection of explosives with a superamplification effect and a low detection limit.

High Throughput Preparation of UV-Protective Polymers from Essential Oil Extracts via the Biginelli Reaction

A high throughput (HTP) system has been developed to exploit new functional polymers. We synthesized 25 monomers in a mini-HTP manner through the tricomponent Biginelli reaction with high yields. The starting materials were five aldehydes extracted from essential oils. The 25 corresponding polymers were conveniently prepared via mini-HTP radical polymerization initially realizing the benefit of HTP methods to quickly fabricate sample libraries. The distinct radical scavenging ability of these Biginelli polymers was evaluated through a HTP measurement to choose the three best radical scavengers. This confirms the superiority of the HTP strategy to rapidly collect and analyze data. The selected polymers have been upgraded and screened according to different requirements for biomaterials and offer water-soluble and biocompatible copolymers that effectively protect cells from the fatal UV damage. This research is a straightforward way to establish new libraries of monomers with abundant diversity. It offers polymers with interesting functionalities. This suggests that a broader study of multicomponent reactions and HTP methods might be useful in many interdisciplinary fields. To the best of our knowledge, this is the first report of a HTP study of the Biginelli reaction to develop a promising polymeric biomaterial, which might have important implications for the organic chemistry and polymer communities.

Pd-Catalyzed One-Pot Stepwise Synthesis of Benzo[b][1,6]naphthyridines from 2-Chloroquinoline-3-carbonitriles Using Sulfur and Amines As Nucleophiles

A palladium-catalyzed one-pot stepwise coupling-annulation reaction of 2-chloroqunoline-3-carbonitriles enabled the direct synthesis of sulfur-substituted benzo[b][1,6]naphthyridines via multiple bond formation. The reaction provided an unusual mode for cyclization as sodium sulfide, a soft nucleophile, preferred to attack on the carbon of the nitrile group rather than on the C-C triple bond. The developed chemistry was extended with the secondary amines as nucleophiles to afford nitrogen-substituted benzo[b][1,6]naphythyridines while primary amines afforded hydroamination products . The hydromination products were transformed to benzo[b][1,6]naphthyridones via a base-mediated cyclization reaction. The  developed protocol features inexpensive and easily synthesizable starting materials, easy operations, and a high efficiency and tolerance to a broad range of substrates.

Influence of Endo- and Exocyclic Heteroatoms on Stabilities and 1,3-Dipolar Cycloaddition Reactivities of Mesoionic Azomethine Ylides and Imines

The geometries, stabilities, and 1,3-dipolar cycloaddition reactivities of 24 mesoionic azomethine ylides and imines were investigated using density functional theory calculations at the M06-2X/6-311+G-(d,p)/M06-2X/6-31G-(d) level. The computed structures highlight how the commonly used "aromatic" resonance form should be replaced by two more accurate resonance structures. Stabilities of the dipoles were assessed by various homodesmotic schemes and are consistent with these compounds being nonaromatic. The activation free energies with ethylene or acetylene range from 11.8 to 36.6 kcal/mol. Within each dipole type, the predicted cycloaddition reactivities correlate with the reaction energies and the resonance stabilization energies provided by the various substituents. Endocyclic (X) heteroatoms increase the reactivity of the 1,3-dipoles in the order of O > NH ≅ S, whereas exocyclic (Y) substituents increase it in the order of CH₂ > NH > O > S. Distortion/interaction analysis indicated that the difference in reactivity between differently substituted 1,3-dipoles is driven by distortion, whereas the difference between azomethine ylides and imines is related to lower interaction energies of imines with the dipolarophiles.

Copper-Catalyzed Sulfonyl Azide-Alkyne Cycloaddition Reactions: Simultaneous Generation and Trapping of Copper-Triazoles and -Ketenimines for the Synthesis of Triazolopyrimidines

First simultaneous generation and utilization of both copper-triazole and -ketenimine intermediates in copper-catalyzed sulfonyl azide-alkyne cycloaddition reactions is achieved for the one-pot synthesis of triazolopyrimidines via a novel copper-catalyzed multicomponent cascade of sulfonyl azides, alkynes, and azirines. Significantly, the reaction proceeds under very mild conditions in good yields.

Fluorescent Cell-Conjugation by a Multifunctional Polymer: A New Application of the Hantzsch Reaction

Multicomponent reactions (MCRs) can form unique structures with interesting functions, therefore, multifunctional polymers might be simply prepared using MCRs as coupling tools to simultaneously link and generate different functional groups. To verify this concept, a new fluorescent polymer containing phenylboronic acid has been facilely prepared via a one pot method by combining the Hantzsch reaction with reversible addition-fragmentation chain transfer (RAFT) polymerization. The Hantzsch-RAFT system has been found robust to smoothly achieve predesigned multifunctional polymer, which can be used for cell conjugation through the interaction between phenylboronic acid and glycoprotein on cell membrane. The conjugated cells could be directly observed due to the fluorescent Hantzsch moiety in the polymer chain, demonstrating a new application of the old Hantzsch reaction (>130 years) outside organic chemistry. Meanwhile, the conjugated cells remained excellent dispersity in the presence of coagulation protein (lectin), implying that multifunctional polymer a possible anticoagulant for cell separation. We believe that the current research paves a new way to exploit new applications of MCRs in interdisciplinary fields and might prompt the development of other multifunctional polymers based on different MCRs.

Metal-Free Multicomponent Tandem Polymerizations of Alkynes, Amines, and Formaldehyde toward Structure- and Sequence-Controlled Luminescent Polyheterocycles

Sequence-controlled polymers, including biopolymers such as DNA, RNA, and proteins, have attracted much attention recently because of their sequence-dependent functionalities. The development of an efficient synthetic approach for non-natural sequence-controlled polymers is hence of great importance. Multicomponent polymerizations (MCPs) as a powerful and popular synthetic approach for functional polymers with great structural diversity have been demonstrated to be a promising tool for the synthesis of sequence-controlled polymers. In this work, we developed a facile metal-free one-pot multicomponent tandem polymerization (MCTP) of activated internal alkynes, aromatic diamines, and formaldehyde to successfully synthesize structural-regulated and sequence-controlled polyheterocycles with high molecular weights (up to 69 800 g/mol) in high yields (up to 99%). Through such MCTP, polymers with the in situ generated multisubstituted tetrahydropyrimidines or dihydropyrrolones in the backbone and inherent luminescence can be easily obtained with high atom economy and environmental benefit, which is inaccessible by other synthetic approaches.

Polymer synthesis by mimicking nature's strategy: the combination of ultra-fast RAFT and the Biginelli reaction

A two-stage method has been developed by mimicking nature's protein synthesis strategy to prepare plenty of polymers using limited monomers.

Post-polymerization modification via the Biginelli reaction to prepare water-soluble polymer adhesives

A copolymer precursor containing the β-ketoester moiety has been modified through the Biginelli reaction to get several water-soluble adhesives which are comparable to commercial glues.

The Hantzsch reaction in polymer chemistry: synthesis and tentative application

The recent utilization of the tetra-component Hantzsch reaction in polymer chemistry has been summarized.

Mechanism of the Palladium-Catalyzed Synthesis of Münchnones: The Role of Ligands in N-Acyl Iminium Salt Carbonylation

The palladium-catalyzed carbonylative coupling of imines, acid chlorides, and dipolarophiles can provide efficient routes to prepare nitrogen-containing heterocycles. One challenge in developing this reaction, and in the creation of more active catalyst systems, is the lack of data on how this complex transformation proceeds. To address this, we report here the results of our mechanistic studies on this system, and in particular the formation of mesoionic münchnones. This includes the synthesis of key catalytic intermediates, model reactions, and kinetic studies that support the role of these compounds in catalysis. Together, these studies provide a clear picture of the impact of catalyst structure, ligands, and palladium nanoparticles on facilitating the carbonylation of in situ generated iminium salts, and suggest an avenue for the creation of more active catalyst systems.

Metal-Free, Multicomponent Synthesis of Pyrrole-Based π-Conjugated Polymers from Imines, Acid Chlorides, and Alkynes

Multicomponent coupling reactions (MCRs) are becoming increasingly used in the synthesis of macromolecules, as they can allow the rapid generation of libraries of materials as a method to tune properties. MCRs could prove particularly useful in the synthesis of π-conjugated polymers in which structural changes are necessary for fine-tuning of electronic properties. We describe here the first metal-free multicomponent approach to conjugated polymers. This reaction exploits the coupling of imines, acid chlorides, and (catechyl)PPh to generate phospha-münchnone-containing polymers, which can be converted to poly(pyrroles) via cycloaddition. The platform allows for the efficient synthesis of families of high molecular weight polymers in one step from readily available monomers.