Nucleophilic Ring-opening Reaction Research Articles

Self-healing, recoverable epoxy elastomers and their composites with desirable thermal conductivities by incorporating BN fillers via in-situ polymerization

Thiol-epoxy elastomers were firstly prepared by thiol-epoxide nucleophilic ring-opening reaction, and the micron boron nitride (mBN) fillers were then introduced into the above system via in-situ polymerization, finally to prepare the highly thermally conductive, self-healing and recoverable mBN/thiol-epoxy elastomer composites by hot-pressing method. Results revealed that the thiol-epoxide reaction was highly efficient and stable. The obtained mBN/thiol-epoxy elastomer composite with 60 wt% mBN fillers presented the optimal thermal conductivity (λ of 1.058 W/mK), excellent self-healing effect & efficiency which is achieved via transesterification reaction (Tensile strength after self-healing could maintain at more than 85% compared to that of original composites), wonderful recoverable performance (Tensile strength after post forming could maintain over 70% compared to that of original composites) and good thermal stability (Theat-resistance index, THRI of 149.9 °C). And the improvement in λ value of the mBN/thiol-epoxy elastomer composites was beneficial to the promotion of the self-healing systems relying on thermal response.

Hydrolysis kinetics of epoxypropyltrimethylammonium chloride in ethanol/water solution system

NaOH-based hydrolysis of epoxypropyltrimethylammonium chloride (ETA) was carried out in a batch reactor using ethanol/water system. The analytic technique, headspace-gas chromatography, was employed in order to follow the time evolution of ETA aqueous solution. Various effects on hydrolysis degree, such as, molar ratio of ethanol/water, NaOH concentration, reaction temperature, and dosage of hydrolysis product (2,3-dihydroxypropyl trimethylammonium chloride) were investigated. And then the kinetic model of the hydrolysis of ETA was developed and the possible mechanism of nucleophilic ring opening reaction was proposed. Furthermore, the model parameters of the process were also determined by data fitting. The results show that ETA hydrolysis follows the pseudo-first order law and kinetic model agrees well with the experimental results. Therefore, based on this kinetic model we could control the hydrolysis degree of ETA during ETA-involved cationic etherification of natural polymer in order to improve the etherification efficiency.

Nucleophilic ring opening reactions of aziridines.

Aziridine ring opening reactions have gained tremendous importance in the synthesis of nitrogen containing biologically active molecules. During recent years, a great effort has been put forward by scientists toward unique bond construction methodologies via ring opening of aziridines. In this regard, a wide range of chiral metal- and organo-catalyzed desymmetrization reactions of aziridines have been reported with carbon, sulfur, oxygen, nitrogen, halogen, and other nucleophiles. In this review, an outline of methodologies adopted by a number of scientists during 2013-2017 for aziridine ring opening reactions as well as their synthetic applications is described.

Synthesis of l-[4-11 C]Asparagine by Ring-Opening Nucleophilic 11 C-Cyanation Reaction of a Chiral Cyclic Sulfamidate Precursor.

The development of a convenient and rapid method to synthesize radiolabeled, enantiomerically pure amino acids (AAs) as potential positron emission tomography (PET) imaging agents for mapping various biochemical transformations in living organisms remains a challenge. This is especially true for the synthesis of carbon-11-labeled AAs given the short half-life of carbon-11 (11 C, t1/2 =20.4 min). A facile synthetic pathway to prepare enantiomerically pure 11 C-labeled l-asparagine was developed using a partially protected serine as a starting material with a four-step transformation providing a chiral five-membered cyclic sulfamidate as the radiolabeling precursor. Its structure and absolute configuration were confirmed by X-ray crystallography. Utilizing a [11 C]cyanide nucleophilic ring opening reaction followed by selective acidic hydrolysis and deprotection, enantiomerically pure l-[4-11 C]asparagine was synthesized. Further optimization of reaction parameters, including base, metal ion source, solvent, acid component, reaction temperature and reaction time, a reliable two-step method for synthesizing l-[4-11 C]asparagine was presented: within a 45±3 min (n=5, from end-of-bombardment), the desired enantiomerically pure product was synthesized with the initial nucleophilic cyanation yield of 69±4 % (n=5) and overall two-step radiochemical yield of 53±2 % (n=5) based on starting [11 C]HCN, and with radiochemical purity of 96±2 % (n=5).

Tn Antigen Mimics by Ring-Opening of Chiral Cyclic Sulfamidates with Carbohydrate C1- S- and C1- O-Nucleophiles.

Starting from commercially available ( S)-isoserine and effectively accessible ( S)-α-methylserine, enantiopure cyclic sulfamidates have been prepared as chiral building blocks for the synthesis of various S- and O-glycosylated amino acid derivatives, including unnatural variants of the Tn antigen, through highly chemo-, regio-, and stereoselective nucleophilic ring-opening reactions with carbohydrate C1- S- and C1- O-nucleophiles.

Reaction of o‐Carboryne with Furans: Facile Synthesis of Carborane‐ Fused Oxanorbornenes and Their Derivatives

o‐Carboryne (1,2‐dehydro‐o‐carborane) is a very useful synthon for the synthesis of a variety of carborane‐functionalized molecules. Diels‐Alder reaction of o‐carboryne with furans gave a series of carborane‐fused oxanorbornenes in moderate to high yields using 1‐OTf‐1,2‐C2B10H11 as carboryne precursor. The resultant cycloadducts can undergo hydrogenation, cyclic oxidation, bromination, [4 + 2]/[2 + 2] cycloaddition and nucleophilic ring opening reaction to afford a variety of highly functionalized carboranes that may find applications as useful basic units in medicine and materials science.

Silica/alginate hybrid biomaterials and assessment of their covalent coupling

Organic–inorganic hybrid materials composed of co-networks of biodegradable polymer and silica have potential to combine the properties of an elastic organic polymer and inorganic silica. The nanoscale interaction of the co-networks and formation of covalent bonds between them are expected to provide tailored mechanical properties and congruent degradation. Alginate is a natural polymer commonly used in tissue engineering applications due to its good biocompatibility and biodegradability. In this work we present new alginate–silica hybrids prepared through nucleophilic ring opening reaction of 3-glycidoxypropyl trimethoxysilane (GPTMS) by carboxylic groups of alginate and incorporation of this functionalized alginate into the sol–gel process to make a hybrid. The role of the GPTMS is to provide organic/inorganic covalent coupling. The reaction of alginate with GPTMS was followed using NMR, FTIR and ToF-SIMS and the dissolution behaviour, bioactivity and mechanical properties of the resultant alginate–silica hybrid monoliths were evaluated. While mechanical strength was high with values of 110–242MPa comparable to that of cortical bone, the amount of GPTMS coupling to the alginate was low, with the rest of the GPTMS forming diols or a separate network.

BF3⋅OEt2‐Promoted Annulation for Substituted 2‐Arylpyridines as Potent UV Filters and Antibacterial Agents

AbstractA simple and efficient BF3⋅OEt2 mediated methodology for the construction of diverse 2‐phenylpyridines bearing benzophenone moieties from readily available 3‐formylchromones and phenylacetylenes in wet acetonitrile was developed. The nitrogen source for the pyridine construction was derived from acetonitrile. This one‐pot protocol proceeds via [3+2+1] annulation through cascade nucleophilic addition, hydrolysis, Michael‐type addition, ring opening, and elimination reactions. The synthesized compounds may have applications as UV filters and exhibit potent antibacterial activities.magnified image

2-Amino homopropargyl alcohols from the highly regioselective Ag2CO3-catalyzed nucleophilic openings of alkynyl epoxides by amines

The nucleophilic ring opening reaction of propargyl epoxides by amines based on a silver catalyst is presented. The reaction takes place under mild conditions and features a high regioselectivity to provide an effective method for the synthesis of 2-amino homopropargyl alcohols in moderate to high yields.

Electrophilic Ring Opening of Small Heterocycles

Small heterocycles, such as epoxides, aziridines, and ox­etanes are among the most useful building blocks in organic synthesis. Through electrophilic ring opening of these molecules, various electrophilic functional groups can be installed, which cannot be achieved via classic nucleophilic ring-opening reactions. In this review, the developments of electrophilic ring opening of small heterocycles are surveyed and organized according to the types of metal promoters.1 Introduction2 Electrophilic Ring Opening of Small Heterocycles Using Stoichiometric Metals2.1 Lithium-Mediated Electrophilic Ring Opening of Epoxides and Oxetanes2.2 Chromium-Mediated Electrophilic Ring Opening of Vinyl Epoxides2.3 Tin-Mediated Electrophilic Ring Opening of Vinyl Epoxides2.4 Samarium-Mediated Electrophilic Ring Opening of Vinyl and Alkynyl Epoxides2.5 Titanium-Mediated Electrophilic Ring Opening of Epoxides2.6 Platinum, Palladium, and Nickel-Mediated Electrophilic Ring Opening of 1,1-Dimethyl Ethylene Oxide3 Catalytic Electrophilic Ring Opening of Small Heterocycles3.1 Titanium-Catalyzed Electrophilic Ring Opening of Epoxides3.2 Palladium-Catalyzed Electrophilic Ring Opening of Vinyl and Alkynyl Small Heterocycles3.3 Iron-Catalyzed Electrophilic Ring Opening of Oxetanes3.4 Scandium-Catalyzed Electrophilic Ring Opening of Vinyl Epoxides3.5 Iridium-Catalyzed Electrophilic Ring Opening of 2-Methyl 2-Vinyl­oxiranes3.6 Nickel-Catalyzed Electrophilic Ring Opening of Epoxides and Aziridines3.7 Nickel–Titanium-Cocatalyzed Electrophilic Ring Opening of Epoxides4 Summary

Preparation of a novel radiotracer targeting the EphB4 receptor via radiofluorination using spiro azetidinium salts as precursor

The visualization of Eph receptors, which are overexpressed in various tumor entities, using selective small molecule Eph inhibitors by means of positron emission tomography is a promising approach for tumor imaging. N-(Pyrimidinyl)indazolamines represent a class of compounds, which are known to have high affinity especially for the EphB4 receptor. Radiofluorination of these compounds could provide a highly specific imaging agent and was investigated using a classical nucleophilic introduction of [18 F]fluoride as well as a less common nucleophilic ring-opening reaction of azetidinium salts. In the past, radiofluorinations using azetidinium precursors were demonstrated to result in high radiochemical yields in short periods. For this purpose, an azetidinium precursor based on the N-(pyrimidinyl)indazolamine lead compound was developed, and radiofluorination was successfully accomplished. The respective [18 F]radiotracer was quickly prepared with high radiochemical purity >97% and in a radiochemical yield of 34%.

Synthesis of Poly(glycidyl 2-ylidene-acetate) and Functionalization by Nucleophilic Ring-Opening Reactions

Rhodium-mediated C1 polymerization of glycidyl 2-diazoacetate resulted in the novel functional polymethylene poly(glycidyl 2-ylidene-acetate), the first functional polymethylene suitable for a subsequent controlled post-polymerization modification at moderate reaction conditions via nucleophilic ring-opening of the epoxide. Nucleophilic ring-opening reactions with water, various amines, and thiols were examined. Even bulky nucleophiles such as α-aminodiphenylmethane reacted quantitatively, resulting in densely packed functional polymers. The obtained results were compared with previously published results on post-polymerization modification of poly(glycidyl methacrylate). Contradictory to the expectations, epoxide ring-opening with primary amines led to soluble products when the C1 polymer poly(glycidyl 2-ylidene-acetate) was employed, while the same reaction with the C2 polymer poly(glycidyl methacrylate) resulted in gelation.

Fabrication of color changeable CO2 sensitive nanofibers

A CO2 sensor was fabricated by attaching CO2-sensitive spiropyran groups onto versatile photo-crosslinked poly(glycidyl methacrylate) (PGMA) precursor nanofibers via a nucleophilic ring-opening reaction.

Nucleophilic ring-opening reactions of trans-2-aroyl-3-aryl-cyclopropane-1,1-dicarboxylates with hydrazines.

trans-2-Aroyl-3-aryl-cyclopropane-1,1-dicarboxylates when treated with arylhydrazines in refluxing EtOH gave dihydropyrazoles, whereas with hydrazines in refluxing AcOH, they formed cyclopropane-fused pyridazinones. Although in both cases the corresponding hydrazones are formed initially, the former case involves a subsequent 5-exo-tet nucleophilic ring-opening, and the later, a 6-exo-trig nucleophilic attack by the other hydrazone nitrogen. The products are obtained in moderate to excellent yields with complete regio-and diastereoselectivity.

Post-polymerization modification reactions of poly(glycidyl methacrylate)s

Single and multiple post-polymerization modifications of poly(glycidyl methacrylate) scaffold through the nucleophilic ring-opening reactions of the pendent epoxide groups are described.

Application of HPLC for the screening of separation of new macrocyclic systems

GRAPHICAL ABSTRACT

Ring opening of sugar-derived epoxides by TBAF/KHF2: An attractive alternative for the introduction of fluorine into the carbohydrate scaffold

A stable and commercially available reagent mixture, composed of tetrabutylammonium bifluoride/potassium bifluoride (TBAF/KHF2), was found to be effective for the nucleophilic ring opening reactions of sugar-derived epoxides with fluoride. Different sugar-derived epoxide precursors, including 1-thio-glycosides can be ring-opened to afford fluorinated carbohydrate products in high yields and in short reaction times.

Functionalization of Alkenes through Telescoped Continuous Flow Aziridination Processes.

Alkenes can be efficiently aziridinated using highly soluble iminoiodane derivatives under continuous flow conditions. By combining the aziridine generation with nucleophilic ring opening reactions, a variety of products can be made without the need to handle or isolate these potentially hazardous intermediates. Additionally, this chemistry can be used to make and use aziridines that are difficult to isolate and purify because of their high reactivity.

2-Methyl-4/5-nitroimidazole derivatives potentiated against sexually transmitted Trichomonas: Design, synthesis, biology and 3D-QSAR study

Trichomoniasis is the most prevalent, non-viral sexually transmitted diseases (STD) caused by amitochondriate protozoan Trichomonas vaginalis. Increased resistance of T. vaginalis to the marketed drug Metronidazole necessitates the development of newer chemical entities. A library of sixty 2-methyl-4/5-nitroimidazole derivatives was synthesized via nucleophilic ring opening reaction of epoxide and the efficacies against drug-susceptible and -resistant Trichomonas vaginalis were evaluated. All the molecules except two were found to be active against both susceptible and resistant strains with MICs ranging 8.55–336.70 μM and 28.80–1445.08 μM, respectively. Most of the compounds were remarkably more effective than the standard Metronidazole. This study analyzes the in vitro and in vivo activities of the new 5-nitroimidazoles, which were found to be safe against human cervical HeLa cells with good selectivity index. The exploration of SAR by the synthesis of four different prototypes and 3D-QSAR study has shown the importance of prototype 1 over other prototypes.

Maleimide-functionalized closo-dodecaborate albumin conjugates (MID-AC): Unique ligation at cysteine and lysine residues enables efficient boron delivery to tumor for neutron capture therapy

Maleimide-conjugating closo-dodecaborate sodium form 5c (MID) synthesized by the nucleophilic ring-opening reaction of closo-dodecaborate-1,4-dioxane complex 2 with tetrabutylammonium (TBA) azide was found to conjugate to free SH of cysteine and lysine residues in BSA under physiological conditions, forming highly boronated BSA that showed high and selective accumulation in tumor and significant tumor growth inhibition in colon 26 tumor-bearing mice subjected to thermal neutron irradiation.