Subsequent Ring-opening Reaction Research Articles

Enhanced cycloaddition between CO2 and epoxide over a bismuth-based metal organic framework due to a synergistic photocatalytic and photothermal effect

The cycloaddition reaction between CO2 and epoxide is an efficient way to convert CO2 into high value-added chemicals. Therefore, it is particularly important to develop efficient catalysts that can catalyze the reaction under mild conditions. In this work, a metal–organic framework (Bi-HHTP, consisting of bismuth (Bi) as metal dots and 2,3,6,7,10,11-hexahydroxy-triphenylene (HHTP) as organic linkers) with zigzagging corrugated topology was successfully synthesized, which shows excellent catalytic activity under visible light irradiation. Various characterizations suggest that the excellent activity is derived from the following reasons: (1) the abundant exposed Bi sites provide Lewis sites for adsorption of epoxides and CO2; (2) the free holes produced over Bi-HHTP under light irradiation which could oxidize epoxide, which consequently facilitateing the subsequent ring-opening reaction; and (3) the existence of synergistic photocatalytic and photothermal effect in Bi-HHTP. This study provides a new avenue of developing bismuth-based metal organic frameworks to promote the efficiency of cycloaddition of CO2 under mild conditions.

Tung oil-based waterborne UV-curable coatings via cellulose nanofibril stabilized Pickering emulsions for self-healing and anticorrosion application

In this study, waterborne UV-curable coatings with self-healing properties based on transesterification were prepared using renewable biomass resources for anti-corrosion application. Tung oil (TO)-based oligomer (TMHT) was synthesized through Diels-Alder reaction of TO with maleic anhydride, subsequent ring opening reaction with hydroxyethyl acrylate (HEA), and final neutralize reaction with triethylamine. A series of waterborne UV-curable coatings were prepared from cellulose nanofibrils (CNF) stabilized TMHT-based Pickering emulsions after drying and UV light-curing processes. It is suggested that CNF significantly improved the storage stability of Pickering emulsions. The obtained waterborne UV-curable coatings with CNF of 1–3 wt% exhibited remarking coating and mechanical performance (pencil hardness up to 5 H, adhesion up to 2 grade, flexibility of 2 mm, tensile strength up to 11.6 MPa, etc.), great transmittance (82.3 %–80.8 %) and great corrosion resistance (|Z|0.01Hz up to 5.4 × 106 Ω·cm2). Because of the presence of the dynamic ester bonds in TMHT, the coatings exhibited excellent self-healing performance (78.05 %–56.34 %) at 150 °C without catalyst and external force. More importantly, the |Z|0.01Hz of the self-healing coating was higher than that of the scratched coating, indicating that the self-healing performance could extend the service life of the coating in corrosion resistant application.

Castor oil-based multi-functional monomers and their application in polyamide design

The design of functional monomers and their functional polymer materials from renewable biomass is gaining more and more attention. This work describes a simple and efficient method to synthesis multi-functional monomers derived from castor oil (Ricinus communis L). Methyl undecylenate was used as starting materials to synthesize epoxy methyl undecylenate monomer via double-bonded epoxidation, and subsequent ammonia ring opening reaction were conducted subsequently to obtain long-chain multi-functional monomer. The prepared multi-functional monomer was applied to design functional polymers by melt polycondensation. For self-condensation, the hydroxyl and secondary amine group of the multi-functional monomer can react with the ester group to form cross-linked polyamide, which possess elastic recovery of up to 97 % after five cycles of stretching. When the multi-functional monomer was copolymerized with 1, 6-hexamethylenediamine, functional polyamide with tensile strength of 43 MPa and elongation at break of 265 % was obtained.

Reassembly of Unsaturated C–C Bonds by a Cutting/Insertion Cascade

AbstractThe reassembly of unsaturated C–C bonds has attracted widespread attention from synthetic chemists due to its advantages of unique reactivity, easy handling, and high atom and step economies. We recently explored a cutting/insertion cascade as a means of introducing a new C1 source and constructing functionalized 1,4-keto aldehyde and 2H-furan derivatives through cyclopropanation of enamines with various carbene precursors and subsequent ring-opening reactions in situ. Aminocyclopropanes are believed to be involved as key intermediates in these transformations. This Synpacts article outlines our recent contributions to this increasingly important research area.1 Introduction2 Cleavage of Enamine C=C Double Bonds and Hydrolysis to 1,4-Keto Aldehydes3 Cleavage of Enamine C=C Double Bonds and Cyclization to 2H-Furans4 Cleavage of Ynone/Ynoate C≡C Triple Bonds5 Conclusion

Effect of methyl substituents, ring size, and oxygen on bond dissociation energies and ring-opening kinetics of five- and six-membered cyclic acetals

The demand for clean and highly efficient fuels stimulates the development of novel fuels for the next generation. With the emergence of new catalytic methods, the selective synthesis of cyclic acetals made them promising fuel candidates. The present work provides systematic and consistent calculations of bond dissociation energies for 1,3-dioxolane and 1,3-dioxane and their substituted derivatives. Rate constants of subsequent ring-opening reactions of the formed fuel radicals have been calculated to facilitate the understanding of initial fuel consumption pathways. We found that the CH bond on the carbon that is in between two oxygens will always be the weakest bond to be broken. The inclusion of two oxygens in the ring slightly changes the strain in the ring structure. However, the trend that the BDEs increase from five to six-membered ring species still exists in cyclic acetals. The reason is a smaller eclipsing strain in the five-membered radicals relative to the parent molecules. For the subsequent ring-opening reactions of the formed radicals, the radical site and the position of the substitution have a major impact. The results of our study facilitate a deeper understanding of the effect of methyl substituents, ring size, and oxygen on the reactivity of five- and six-membered cyclic acetals as well as provide accurate kinetic data for the mechanism development of these potential fuels.

Synthesis of Polyacrylamide‐Based Redox Active Cryogel Using Click Chemistry and Investigation of Its Electrochemical Properties

AbstractFerrocene (Fc) functionalization of macroporous polyacrylamide‐based cryogel (PAAm‐Epx) is achieved by click chemistry. For this purpose, firstly, PAAm‐Epx cryogel with azide functionality (PAAm‐N3) is prepared by using acryalmide (AAm) as the monomer and allyl glycidyl ether (AGE) as the co‐monomer followed by subsequent ring opening reaction of epoxide ring of AGE in acidic medium. Azide groups of PAAm‐N3 is then modified with ethynyl ferrocene, leading to the redox active cryogel (PAAm−Fc) together with preserving the unique characteristic properties of the virgin PAAm‐Epx cryogel. Swelling, mechanical and morphological behaviours of PAAm‐Epx, PAAm‐N3 and PAAm−Fc are investigated. Detailed characterization of the PAAm−Fc is carried out by several techniques such as FTIR (Fourier Transform Infrared Spectroscopy), Scanning electron microscopy with energy dispersive X‐ray spectroscopy (SEM‐EDX), Inductively Coupled Plasma Optical Emmision Spectrometry (ICP‐OES, Cyclic (CV), and Differential Pulse Voltammetry (DPV). Electrochemical analysis confirms the electroactivity and the presence of chemically linked ferrocene unit to the cryogel.

Synthesis of a Cyclic Dinucleotide Analogue with Ambiguous Bases, 5-Aminoimidazole-4-carboxamide.

Cyclic dinucleotides (CDNs) are second messengers composed of two purine nucleotides. In recent years, the structural diversity of CDNs and their functionality in biological processes are being intensely studied. Herein we report the chemical synthesis of cyclic di-5-aminoimidazole-4-carboxamide-1-β-d-ribofuranosyl monophosphate (c-di-ZMP) (1), which consists of two 5-amino-4-imidazolecarboxamide ribonucleotides (Z-ribonucleotides) linked via two phosphodiester linkages. Construction of the CDN skeleton with an N1-dinitrophenylhypoxanthine base (HxaDNP-base) by phosphoramidite chemistry and the subsequent ring-opening reaction of HxaDNP-base successfully yielded the desired 1.

Epoxide Syntheses and Ring-Opening Reactions in Drug Development

This review concentrates on success stories from the synthesis of approved medicines and drug candidates using epoxide chemistry in the development of robust and efficient syntheses at large scale. The focus is on those parts of each synthesis related to the substrate-controlled/diastereoselective and catalytic asymmetric synthesis of epoxide intermediates and their subsequent ring-opening reactions with various nucleophiles. These are described in the form of case studies of high profile pharmaceuticals spanning a diverse range of indications and molecular scaffolds such as heterocycles, terpenes, steroids, peptidomimetics, alkaloids and main stream small molecules. Representative examples include, but are not limited to the antihypertensive diltiazem, the antidepressant reboxetine, the HIV protease inhibitors atazanavir and indinavir, efinaconazole and related triazole antifungals, tasimelteon for sleep disorders, the anticancer agent carfilzomib, the anticoagulant rivaroxaban the antibiotic linezolid and the antiviral oseltamivir. Emphasis is given on aspects of catalytic asymmetric epoxidation employing metals with chiral ligands particularly with the Sharpless and Jacobsen–Katsuki methods as well as organocatalysts such as the chiral ketones of Shi and Yang, Pages’s chiral iminium salts and typical chiral phase transfer agents.

Enzyme-mimetic self-catalyzed polymerization of polypeptide helices

Enzymes provide optimal three-dimensional structures for substrate binding and the subsequent accelerated reaction. Such folding-dependent catalytic behaviors, however, are seldom mechanistically explored with reduced structural complexity. Here, we demonstrate that the α-helix, a much simpler structural motif of enzyme, can facilitate its own growth through the self-catalyzed polymerization of N-carboxyanhydride (NCA) in dichloromethane. The reversible binding between the N terminus of α-helical polypeptides and NCAs promotes rate acceleration of the subsequent ring-opening reaction. A two-stage, Michaelis–Menten-type kinetic model is proposed by considering the binding and reaction between the propagating helical chains and the monomers, and is successfully utilized to predict the molecular weights and molecular-weight distributions of the resulting polymers. This work elucidates the mechanism of helix-induced, enzyme-mimetic catalysis, emphasizes the importance of solvent choice in the discovery of new reaction type, and provides a route for rapid production of well-defined synthetic polypeptides by taking advantage of self-accelerated ring-opening polymerizations.

Radiation Synthesis of Pentaethylene Hexamine Functionalized Cotton Linter for Effective Removal of Phosphate: Batch and Dynamic Flow Mode Studies

A quaternized cotton linter fiber (QCLF) based adsorbent for removal of phosphate was prepared by grafting glycidyl methacrylate onto cotton linter and subsequent ring-opening reaction of epoxy groups and further quaternization. The adsorption behavior of the QCLF for phosphate was evaluated in a batch and column experiment. The batch experiment demonstrated that the adsorption process followed pseudo-second-order kinetics with an R2 value of 0.9967, and the Langmuir model with R2 value of 0.9952. The theoretical maximum adsorption capacity reached 152.44 mg/g. The experimental data of the fixed-bed column were well fitted with the Thomas and Yoon–Nelson models, and the adsorption capacity of phosphate at 100 mg/L and flow rate 1 mL/min reached 141.58 mg/g. The saturated QCLF could be regenerated by eluting with 1 M HCl.

Facile Fabrication of N-Methyl-D-Glucamine Grafted HDPE Particle as Adsorbent for Boron Removal from Aqueous Solution

Glycidyl methacrylate (GMA) was grafted onto the surface of HDPE particles by radiation grafting and emulsion graft copolymerization. And subsequent ring-opening reaction of expoxy groups in poly-GMA graft chains with N-methylglucamine (NMG) was conducted to synthesis the boron adsorbent. The synthesis condition (radiation dose and NMG concentration) was optimized and characterized by IR and SEM. Adsorption behaviors of the boron adsorbent for boron removal presented that adsorption kinetics was well described by pseudo-second-order kinetic mode. The adsorption isothermal was well fitted with both Langmuir and Freundlich isotherm models. The adsorption capacity for boron reached 15.63 mg/g at optimal pH 8. Dynamic experiment revealed that boron could be efficiently adsorbed by the boron adsorbent and fully desorbed using 13 BV of 1 mol/L HCl.

Recyclable Polymeric Thin Films for the Selective Detection and Separation of Picric Acid.

Thin-film probes have been developed for the reversible detection and separation of picric acid (PA) with extreme sensitivity in aqueous media. The free radical copolymerization of dimethylacrylamide (DMA), benzophenone acrylamide (BPAM), and glycidyl methacrylate (GMA) with a feed ratio of 95:1:4 yielded [p(DMA- co-BPAM- co-GMA)] (P1). P1 was transformed to the final polymeric probe, P2, by a subsequent ring-opening reaction between N-(pyren-1-yl-methyl)propan-1-amine (Py-PA)with the epoxide unit of P1. P2 exhibited rapid and selective sensing properties toward PA in aqueous media via turn-off fluorescence emission. The detection sensitivity was tuned precisely by varying the pH of the solution. After the immobilization of P2 on a quartz slide by spin-coating, followed by exposure to UV light, the resulting film exhibited an attogram-level detection limit toward PA. The photoinduced electron transfer together with an energy-transfer process between PA and the pyrene units of P2 were maximized by the strong π-π stacking of pyrene units of P2, which, in turn, induced rapid exciton energy diffusion. Furthermore, the separation of PA from the mixture of the various nitroaromatic compounds by the P2 film was achieved. Whereas the detection process of PA was reversible and repeatable over multiple cycles, the P2 film could be recycled.

Fabrication of Hydrophilic and Hydrophobic Sites on Polypropylene Nonwoven for Oil Spill Cleanup: Two Dilemmas Affecting Oil Sorption.

This article mainly deals with the following dilemmas, which affect oil sorption and sorbent preparation: (1) hydrophobization could facilitate oil sorption but has adverse impacts on emulsion sorption; (2) micropores of conventional oil sorbent do not exhibit effective emulsion sorption. To solve the above contradictions, hydrophilic and hydrophobic sites were fabricated onto polypropylene (PP) nonwoven through electron beam radiation and subsequent ring-opening reaction. Further, a similar structure without a hydrophilic site was constructed as comparison to verify the dilemmas. An oil sorption and emulsion adsorption experiment revealed that the PP nonwoven with specific hydrophilic and hydrophobic sites is more suitable for oil cleanup. The hydrophobic site preserved its hydrophobicity and sorption capacity, and the hydrophilic site on PP surface effectively increased the affinity between the hydrophilic interface of emulsion and sorbent. The overlapped and intertwined structures could provide spaces large enough to accommodate oil and emulsion. In addition, the oil and emulsion sorption behaviors were systematically analyzed. The PP nonwoven fabricated in this study may find practical application in the cleanup of oil spills and the removal of organic pollutants from water surfaces.

Adsorption of phthalic acid esters (PAEs) by amphiphilic polypropylene nonwoven from aqueous solution: The study of hydrophilic and hydrophobic microdomain

A kind of amphiphilic polypropylene nonwoven with hydrophilic and hydrophobic microdomain was prepared through electron beam induced graft polymerization and subsequent ring opening reaction and then utilized in the adsorption of phthalic acid esters (PAEs). To elucidate the superiority of such amphiphilic microdomain, a unique structure without hydrophilic part was constructed as comparison. In addition, the adsorption behaviors including adsorption kinetics, isotherms and pH effect were systematically investigated. The result indicated that the amphiphilic structure and the synergy between hydrophilic and hydrophobic microdomain could considerably improve the adsorption capacities, rate and affinity. Particularly the existence of hydrophilic microdomain could reduce the diffusion resistance and energy barrier in the adsorption process. These adsorption results showed that the amphiphilic PP nonwoven have the potential to be used in environmental application.

Development of Diversity-Enhanced Extracts of Curcuma zedoaria and Their New Sesquiterpene-like Compounds

Through the combination of natural products chemistry and diversity-oriented synthesis, a new approach, diversity-enhanced extracts, for increasing the diversity of natural product-like compounds is proposed. They are prepared from chemical reactions that remodel molecular scaffolds directly on extracts of natural resources. This method was applied to terpenes extracted from Curcuma zedoaria. Epoxidation and subsequent ring-opening reactions of epoxides were used to modify molecular skeletons. As a result, seven sesquiterpene-like compounds with some containing new molecular skeletons were obtained.

Improved synthesis of (R)-7-hydroxycarvone from (S)-α-pinene

A three-step synthesis of (R)-7-hydroxycarvone (1), which is anticipated to be a valuable building block for the versatile preparation of natural products, is described. Optimization of the reaction conditions for photooxygenation and migration of (S)-α-pinene 2, tetrapropylammonium perruthenate (TPAP) oxidation of the generated alcohol, and a subsequent ring-opening reaction in the presence of Cu(OTf)2 led to the synthesis of 1 with good reproducibility. The desired product 1 was thus obtained in 46% yield over three steps.

Reactions of 7,7,8,8-Tetracyanoquinodimethane with Poly-ynyl Ruthenium and Iron Complexes

The reaction of tetracyanoquinodimethane (TCNQ) with Ru(C≡CC≡CH)(dppe)Cp* (5) at the outer (from Ru) C≡C triple bond gives η1-(butadienyl)ethynyl Ru{C≡CC[CH═C(CN)2]═C6H4═C(CN)2}(dppe)Cp (8), which reacts with a second equivalent of diynyl-Ru complex to give {Ru(dppe)Cp*}{C≡CC[═C6H4═C(CN)2]CH═CHC[═C(CN)2]C≡C}{Ru(dppe)Cp*} (9). The Ph-substituted complexes M{C≡CC≡CPh}(dppe)Cp* (M = Fe 6-Fe, Ru 6-Ru) and Ru{(C≡C)3Ph}(PPh3)2Cp (7) react with TCNQ to give the η1-(butadienyl)ethynyls M{C≡CC[CPh═C(CN)2]═C6H4═C(CN)2}(dppe)Cp (10-Fe, 10-Ru) and Ru{C≡CC[C(C≡CPh)═C(CN)2]═C6H4═C(CN)2}(PPh3)2Cp (11), respectively. Single-crystal X-ray diffraction molecular structure determinations for 8–11 have been carried out. In the Fe series, we suggest that the initial step of the mechanism involves electron transfer to form the [TCNQ]−• salt of the diynyl-iron cation, followed by C–C bond formation to give a zwitterionic intermediate. Isolated products can be rationalized by further reaction involving [2 + 2]-cycloaddition of one of the C═C(CN)2 groups of TCNQ to a C≡C triple bond of the metal poly-ynyl complex and a subsequent ring-opening reaction of the resulting (unobserved) cyclobutenyl intermediate. On the basis of X-ray diffraction data, redox potential determinations, and 57Fe Mössbauer and UV–vis spectroscopies, the electronic structures of the new compounds contain significant contributions from polarized mesomers involving charge transfer from the electron-rich metal–ligand fragment to the cyanocarbon ligand via the conjugated unsaturated carbon linker.

Aqueous ring opening of N-tosylaziridine with aniline derivatives

A series of N-(p-X-phenyl)-N′-(p-toluenesulfonyl)1,2-ethylenediamines compounds, TsN(H)CH2CH2N(H)PhX, were synthesized by the uncatalyzed ring opening reaction of N-tosylaziridine with p-X-aniline derivatives in pure water at 50°C. No solvolysis product was observed and the only side product was that of a subsequent ring opening reactions of N-tosylaziridine with the product anilines leading to substituted diethylenetriamines, XPhN(CH2CH2NTs)2.

Copper bis(oxazolines) as catalysts for stereoselective aziridination of styrenes with N-tosyloxycarbamates

A Cu(I)-catalyzed asymmetric aziridination of styrenes with a chiral N-tosyloxycarbamate has been developed. Double stereodifferentiation was observed and both the N-tosyloxycarbamate substituent and the bis(oxazoline) ligand have a significant effect on the yields and diastereoselectivities. The best results for the aziridination were obtained with electron-deficient styrenes. Subsequent ring-opening reactions of styrene-derived aziridines at the benzylic position were observed with various oxygen and nitrogen nucleophiles under Lewis acid catalysis affording the corresponding products with complete inversion of stereochemistry. The strategy was used to synthesize the β-blocker, (R)-nifenalol.

A Percyanovinylidene−Ruthenium Complex, Ru{═C═C5(CN)3[═C(CN)2]2}(dppe)Cp*

The reaction between Ru(C≡CC≡CAg)(dppe)Cp* and tcne affords a novel percyanovinylidene complex by an unusual decyano-dimerization reaction of the cyanocarbon with the diynyl fragment. This complex is also obtained from tcne and Ru{C≡CC≡C[Au(PPh3)]}(dppe)Cp*, together with Ru{C≡CC[═C(CN)2]C[Au(PPh3)]═C(CN)2}(dppe)Cp*, formed by the anticipated [2 + 2] cycloaddition and subsequent ring-opening reactions.