Alkynyl Groups Research Articles

Hydration of Propargyl Esters Catalyzed by Gold(I) Complexes with Phosphoramidite Calix[4]pyrrole Cavitands as Ligands.

We report the synthesis and characterization of two diastereomeric phosphoramidite calix[4]pyrrole cavitands and their corresponding gold(I) complexes, 2in•Au(I)•Cl and 2out•Au(I)•Cl, featuring the metal center directed inward and outward with respect to their aromatic cavity. We studied the catalytic activity of the complexes in the hydration of a series of propargyl esters as the benchmarking reaction. All substrates were equipped with a six-membered ring substituent either lacking or including a polar group featuring different hydrogen bond acceptor (HBA) capabilities. We designed the substrates with the polar group to form 1:1 inclusion complexes of different stabilities with the catalysts. In the case of 2in•Au(I)•OTf, the 1:1 complex placed the alkynyl group of the bound substrate close to the metal center. We compared the obtained results with those of a model phosphoramidite gold(I) complex lacking a calix[4]pyrrole cavity. We found that for all catalysts, the presence of an increasingly polar HBA group in the substrate provoked a decrease in the hydration rate constants. We attributed this result to the competing coordination of the HBA group of the substrate for the Au(I) metal center of the catalysts.

In situ synthesis of bi-functional NH2-Ti2C3Tx@COF Schottky heterojunction through interfacial electron effects for enhancing U(VI) photoreduction

Reduction of soluble U(VI) to insoluble U(IV) is considered as a promising strategy to avoid uranium contamination. Herein, a bi-functional covalent organic framework based heterojunction (NH2-Ti3C2Tx@COF) was constructed on the amino-modified Ti3C2Tx MXene for efficient photoreduction U(VI) without additional sacrificial agents. Schottky interface with electronic unidirectional channel is established by the formation of local electrophilic/nucleophilic region due to the introduction of reductive COF with alkynyl group, resulting in efficient photogenerated carrier separation and solar energy utilization. More importantly, NH2-Ti3C2Tx with negative charge served as electron collector and transfer channel can effectively surmount the low photocatalytic activity caused by high polarization of imine-linked COFs. Thus, the tailored-made design of NH2-Ti3C2Tx@COF exhibits excellent photocatalytic activity, fast reaction kinetics (removal of 97.8 % in 60 min) and high adsorptive capability (1557.2 mg/g) under the light condition. This multiple-in-one advantage makes well-designed NH2-Ti3C2Tx@COF as a promising capture platform. This work will provide some new insight and inspiration to COF based heterojunctions for enhancing U(VI) capture.

Selective oxidation of sulfides by pyrene-π-anthraquinone conjugated microporous polymer photocatalysis

Enabled by tailorability and aromaticity, conjugated microporous polymers (CMPs) have become increasingly important in photocatalysis. Both pyrene and anthraquinone are essential building blocks of burgeoning photocatalytic materials like CMPs. Herein, alkynyl groups are embedded between pyrene and anthraquinone, affording Py-π-AQ-CMP. Theoretical calculation indicates that the insertion of alkynyl groups adjusts steric hindrance and ameliorates the planar π-conjugation. Notably, the extended π-conjugation generates a narrower band gap and more extensive optical response, enabling Py-π-AQ-CMP with superior charge carrier’s mobility. Gratifyingly, Py-π-AQ-CMP photocatalysis could enable the highly selective oxidation of organic sulfides in methanol. Significantly, driven by blue light, Py-π-AQ-CMP delivers almost twice of the efficiency of Py-AQ-CMP, a CMP without the alkynyl π-bridge. The mechanistic investigation suggests both electron and energy transfers participate in the activation of dioxygen for the oxidation of sulfides. This work highlights that inserting a π-bridge could afford high-performance photocatalysts of CMPs.

Regio- and stereoselective nucleophilic addition reactions of Swaminathan ketone and its methylated analog using organometallic reagents

Herein, we report the regio- and stereoselective nucleophilic addition reactions of Swaminathan ketone 2a and its methylated analog 2b, both of which contain a 6–7 fused carbocyclic enedione moiety. Nucleophilic additions to 2 using generic organometallic reagents, such as Grignard and organolithium reagents, preferentially occurs at the conjugated carbonyl group to afford a range of tert-alcohols with high stereoselectivity. The selectivity observed with 2 was notable when compared to that observed with Wieland–Miescher ketone 1a bearing a decalin framework. A variety of substituents, such as alkyl, alkenyl, alkynyl and aryl groups, can be introduced into 2 using this method. Exceptionally, the allylation reaction of 2 occurred at both the conjugated and non-conjugated carbonyl groups, but this regioselectivity problem was solved using organocopper reagents.

Loops Mediate Agonist-Induced Activation of the Stimulator of Interferon Genes Protein.

The stimulator of interferon genes (STING) is an important therapeutic target for cancer diseases. The activated STING recruits downstream tank-binding kinase 1 (TBK1) to trigger several important immune responses. However, the molecular mechanism of how agonist molecules mediate the STING-TBK1 interactions remains elusive. Here, we performed molecular dynamics simulations to capture the conformational changes of STING and TBK1 upon agonist binding. Our simulations revealed that multiple helices (α5-α7) and especially three loops (loop 6, loop 8, and C-terminal tail) of STING participated in the allosteric mediation of the STING-TBK1 interactions. Consistent results were also observed in the simulations of the constitutive activating mutant of STING (R284S). We further identified α5 as a key region in this agonist-induced activation mechanism of STING. Free-energy perturbation calculations of multiple STING agonists demonstrated that an alkynyl group targeting α5 is a determinant for agonist activities. These results not only offer deeper insights into the agonist-induced allosteric mediation of STING-TKB1 interactions but also provide a guidance for future drug development of this important therapeutic target.

Quaternary Ammonium Salts: Catalysts for Hydrosilylation of Alkynes with Hydrosilanes

AbstractMixing i‐PrI and DABCO in solvent EtCN gave two quaternary ammonium salts (QASs) quantitatively, one of which is monocationic (QAS‐1) and the other is dicationic (QAS‐2). These QASs were found to catalyze hydrosilylation of alkynes with hydrosilanes (HAH) without the aid of metal and metalloid catalysts. This organocatalysis can be applied to a variety of alkynes: terminal/internal aryl and alkyl alkynes with/without a functional group. With dihydrosilanes (H2Si), the HAH occurred with high E‐selectivity through syn addition, which was exclusively observed when using terminal alkyl alkynes, irrespective of a hydrosilane used. A scalable HAH is also feasible. The H−Si unit remaining in alkenylsilanes derived from H2Si is available for dehydrogenative alkynylation and N‐heteroarylation under zinc–pyridine catalysis. This synthetic application delivers unique silicon compounds that have, for instance, alkyl, aryl, alkenyl, and alkynyl groups in a single molecule. Mechanistic studies suggested that alkynes activated by QASs irreversibly react with hydrosilanes that become more nucleophilic by the coordination of EtCN. A radical pathway is unlikely. The QAS catalysts can be recovered and reused at least 5 times.

1,2-Alkynyl Functionalization of Unactivated Alkenes via Diverse Radical-Triggered Functional Group Migration.

We have developed a transition-metal-free radical approach for 1,2-alkynyl functionalization of unactivated alkenes through the combination of 3-exo-dig cyclization with alkynyl migration triggered by in situ-generated diverse radical precursors. This strategy provides a robust toolkit to access a variety of synthetically important α-functionalized alkynyl ketones, simultaneously installing densely functionalized carbonyl, alkynyl, and other various functional groups into the alkenes. The broad substrate scope, which includes distinctly electron-donating or electron-withdrawing alkynyl migrating groups, excellent functional group compatibility, and remarkable selectivity make this protocol practical and attractive.

Single-microbead space-confined digital quantification strategy (SMSDQ) for counting microRNAs at the single-molecule level

Quantification of microRNAs (miRNAs) at the single-molecule level is of great significance for clinical diagnostics and biomedical research. The challenges lie in the limits to transforming single-molecule measurements into quantitative signals. To address these limits, here, we report a new approach called a Single Microbead-based Space-confined Digital Quantification (SMSDQ) to measure individual miRNA molecules by counting gold nanoparticles (AuNPs) with localized surface plasmon resonance (LSPR) light-scattering imaging. One miRNA target hybridizes with the alkynyl-modified capture DNA probe immobilized on a microbead (60 μm) and the azide-modified report DNA probe anchored on AuNP (50 nm), respectively. Through the click reaction between the alkynyl and azide group, a single microbead can covalently link the AuNPs in the confined space within the view of the microscope. By digitally counting the light-scattering spots of AuNPs, we demonstrated the proposed approach with single-molecule detection sensitivity and high specificity of single-base discrimination. Taking the advantages of ultrahigh sensitivity, specificity, and the digital detection manner, the approach is suitable for evaluating cell heterogeneity and small variations of miRNA expression and has been successfully applied to direct quantification of miRNAs in one-tenth single-cell lysates and serum samples without RNA-isolated and nucleic acid amplification steps.

Preparation of benzofuran-2-carbohydrazide and its utilization for benzofuran-bearing 1,2,4-triazole and 1,3,4-oxadiazole synthesis

Benzofuran, triazole and oxadiazole spontaneously occur in natural compounds with highly desired bioactivities, such as antibacterial, antifungal, antiviral and anticancer. These cyclic scaffolds happen in a variety of commercial medicines as well as developed drugs in late-stage clinical trials (eg. amiodarone, ramelteon, zibotentan, and ataluren). Benzofuran-bearing triazole and oxadiazole can be synthesized by click reaction, requiring an alkynyl group. The formation of the alkynyl group can be achieved by treating the precursor with sodium azide, a poisonous chemical that needs safe conditions for manipulation. In this study, a simple and convenient reflux-based method for the synthesis of benzofuran-involved triazole and oxadiazole was developed. Firstly, benzofuran-2-carbohydrazide (3) was prepared by the reaction of salicylaldehyde and ethyl chloroacetate, followed by the treatment with hydrazine hydrate. Subsequently, compound (3) reacted with KOH, CS2 and hydrazine hydrate to afford 4-amino-1,2,4-triazole-3-thiol derivative (4), existing in a tautomeric form with its thione isomer (4b) in 1:3 of molar ratio. Intriguingly, the reaction of (3) and 4-fluorobenzaldehyde afforded N'-(4-fluorobenzoyl)-1-benzofuran-2-carbohydrazide (6) instead of 1,3,4-oxadiazole derivatives. Their structures were confirmed by NMR and MS. Altogether, this study implies the potential of using the simple and cost-effective reflux-based method for benzofuran-bearing triazole and oxadiazole synthesis.
 ® 2023 Journal of Science and Technology − NTTU

Self-Assembly and Photothermal Conversion of MetallaRussian Doll and Metalla[2]catenanes Induced via Multiple Stacking Interactions.

A variety of organometallic supramolecular architectures have been constructed over the past decades and their properties were also explored via different strategies. However, the synthesis of metalla-Russian doll is still a fascinating challenge. Herein, a series of new coordination supramolecular complexes, including a metalla-Russian doll, metalla[2]catenanes, and metallarectangles, were synthesized by using meticulously selected Cp*Rh (Cp* = η5-C5Me5) building units (E1, E2, and E3) and three rigid anthracylpyridine ligands (L1, L2, and L3) via a self-assembly strategy. While the combination of the short ligand L1 and E1 or E2 generated two metallarectangles, the longer ligand L2 containing an alkynyl group resulted in two new [2]catenanes, most likely due to which the strong electron-donating effect of alkynyl groups causes self-accumulation. Interestingly, an unusual Russian doll assembly was obtained through the reaction of L3 and E3 based on sextuple π···π stacking interactions. Furthermore, the dynamic structural conversion between [2]catenanes and the corresponding metallarectangles could be observed through concentration-, solvent-, and guest-induced effects. The [2]catenane complexes 4b displayed efficient photothermal conversion efficiency in solution (20.2%), in comparison with other organometallic macrocycles. We believe that π···π stacking interactions generate active nonradiative pathways and promote radiative photodeactivation pathways. This study proves the versatility of half-sandwich building units, not only to build complicated supramolecular topologies but also in effective functional materials for various appealing applications.

β‐Functionalization of 4 a‐aza‐8 a‐boranaphthalene via Iridium‐catalyzed C−H Borylation

AbstractA general method for the functionalization of 4a‐aza‐8a‐boranaphthalene in the position β to the nitrogen atom has been developed. This method is based on a regioselective iridium‐catalyzed C−H activation process for the introduction of a boronate group, which can subsequently be transformed into a variety of aryl or alkynyl groups via cross‐coupling reactions. Selective mono‐ or difunctionalization can be achieved by controlling the reaction conditions during the borylation step. The photophysical properties of the obtained 3‐ or 3,6‐substituted BN‐naphthalenes have been evaluated, and some of them have been found to be significantly fluorescent, with fluorescence quantum yields up to 0.85.

Facile Fabrication of Fluorescent Cellulose with Aggregation‐Induced Emission Characteristic in a CO2 Switchable Solvent

AbstractFabrication of fluorescent cellulose with aggregation‐induced emission (AIE) characteristics is usually achieved by grafting tetraphenylethylene (TPE) to the cellulose backbone using TPE derivatives with highly active functional groups such as carboxylic, isothiocyanate, and alkynyl groups. However, besides the complicated synthetic routes of these TPE derivatives, conversion of hydroxyl groups in the cellulose chain to more reactive groups such as amine or azide groups is usually involved, and the resulting products have a degree of substitution (DS) of TPE lower than 0.08. Herein, a facile one‐pot strategy for the grafting of a TPE group to the cellulose backbone with high DS of up to 0.22 in a CO2 switchable solvent under mild reaction conditions is reported. The hydroxyl groups in the cellulose are in situ converted to cellulose carbonate intermediately during the dissolution step. Subsequently, nucleophilic substitution between the intermediate and a halogenated TPE derivative with bromine atom as leaving group is carried out to achieve the effective grafting of TPE. The synthetic route for this promising TPE derivative is much more convenient than those of TPE derivatives reported in previous studies. This work suggests a new and facile pathway for the synthesis of high‐emission fluorescent cellulose with AIE functionality.

Diazulenorubicene as a Non-benzenoid Isomer of peri-Tetracene with Two Sets of 5/7/5 Membered Rings Showing Good Semiconducting Properties.

Non-benzenoid polycyclic aromatic hydrocarbons (PAHs) have received a lot of attention because of their unique optical, electronic, and magnetic properties, but their synthesis remains challenging. Herein, we report a non-benzenoid isomer of peri-tetracene, diazulenorubicene (DAR), with two sets of 5/7/5 membered rings synthesized by a (3+2) annulation reaction. Compared with the precursor containing only 5/7 membered rings, the newly formed five membered rings switch the aromaticity of the original heptagon/pentagon from antiaromatic/aromatic to non-aromatic/antiaromatic respectively, modify the intermolecular packing modes, and lower the LUMO levels. Notably, compound 2 b (DAR-TMS) shows p-type semiconducting properties with a hole mobility up to 1.27 cm2 V-1 s-1 . Moreover, further extension to larger non-benzenoid PAHs with 19 rings was achieved through on-surface chemistry from the DAR derivative with one alkynyl group.

Diazulenorubicene as a Non‐benzenoid Isomer of peri‐Tetracene with Two Sets of 5/7/5 Membered Rings Showing Good Semiconducting Properties

AbstractNon‐benzenoid polycyclic aromatic hydrocarbons (PAHs) have received a lot of attention because of their unique optical, electronic, and magnetic properties, but their synthesis remains challenging. Herein, we report a non‐benzenoid isomer of peri‐tetracene, diazulenorubicene (DAR), with two sets of 5/7/5 membered rings synthesized by a (3+2) annulation reaction. Compared with the precursor containing only 5/7 membered rings, the newly formed five membered rings switch the aromaticity of the original heptagon/pentagon from antiaromatic/aromatic to non‐aromatic/antiaromatic respectively, modify the intermolecular packing modes, and lower the LUMO levels. Notably, compound 2 b (DAR‐TMS) shows p‐type semiconducting properties with a hole mobility up to 1.27 cm2 V−1 s−1. Moreover, further extension to larger non‐benzenoid PAHs with 19 rings was achieved through on‐surface chemistry from the DAR derivative with one alkynyl group.

Frontiers in Copper-promoted C1-functionalization of Tetrahydroisoquinoline Using Cross-dehydrogenative Coupling

Abstract: The site-selective diversification of molecules is a pertinent unresolved issue within the area of organic chemistry. The functionalization of Csp3-H has changed the landscape of synthetic chemistry by enabling effective direct coupling of compounds and reducing chemical waste by avoiding the usage of pre-functionalized compounds. The 1,2,3,4- tetrahydroisoquinoline (THIQ), a molecule with potential bioactivity, has a stereoselective center at the C1 position. However, there is still a fundamental problem with the C1-functionalization of THIQs. To address this, transition metal-catalyzed cross-dehydrogenative coupling (CDC) has evolved into an essential tool because such reactions can be carried out with enantio-, regio-, and stereoselectivity. In particular, copper-promoted CDC reactions have undoubtedly made substantial progress in THIQ chemistry as a selective protocol. The α-Csp3-H bond adjacent to the Natom of THIQs is activated using copper catalysts, followed by dehydrogenative coupling with various alkynyl, alkane, and alkene groups to form the Csp-Csp3, Csp3-Csp3, and Csp3-Csp2 bonds and produce optically active C1-substituted THIQs. The A3 coupling strategies also produce the endo-yne-THIQs with higher selectivity. This critical discussion highlights all recent advancements (between 2010 and 2022) in CDC reactions to THIQs with the substrate scope and plausible mechanistic routes. This study may be extremely useful to scientists and researchers working on copper-promoted CDC.

Synthesis and Determination of Anticancer Activity of Dicobalt Hexacarbonyl 2'-Deoxy-5-alkynylfuropyrimidines.

Dicobalt hexacarbonyl 5-alkynyl furopyrimidine nucleoside analogs, with 4-methylphenyl (p-tolyl) and 4-pentylphenyl substituents attached at the C-6 base position, designed in the form of ribose acetyl esters, were synthesized (42-96%). Attached at the C-5 position were propargyl alcohol, its methyl ether and acetate derivatives, butynol, and the 4-methylphenyl- (p-tolyl) and 4-pentylphenyl-substituted alkynyl groups, which were coordinated to a dicobalt hexacarbonyl unit. The structure of 5-(3-acetoxyprop-1-yn-1-yl)-6-p-tolyl-2'-deoxyribofuranosyl-furo[2,3-d]pyrimidin-2-one was determined by X-ray crystallography. Density functional theory calculations performed on the corresponding derivative yielded geometric parameters for the dicobalt hexacarbonyl adduct of this ligand. The cytotoxic activity of each of dicobalt modified nucleosides on cancer cells of different phenotypes was determined in vitro. The investigated compounds showed antiproliferative effects with median inhibitory concentration (IC50) values in the ranges of 14-90 and 9-50 μM for HeLa and K562 cells, respectively. The formation of reactive oxygen species in the presence of modified nucleosides was determined in K562 cells. The results indicate that the mechanism of action for the studied compounds may be related to the induction of oxidative stress.

Multicolor aptasensors for pesticide multiresidues detection in agricultural products using bioorthogonal surface-enhanced Raman scattering tags

Realizing accurate pesticide multiresidue detection in a complex matrix is still a challenge for point-of-care sensing methods. Herein, we introduced background-free and multicolor aptasensors based on bioorthogonal surface-enhanced Raman scattering (SERS) tags and successfully applied them to analyze multiple pesticide residues. The excellent anti-interference and multiplex capability are due to the application of three bioorthogonal Raman reporters involving 4-ethenylbenzenamine (4-EBZM), Prussian blue (PB) and 2-amino-4-cyanopyridine (AMCP) with alkynyl and cyano groups, which demonstrated apparent Raman shift peaks at 1993 cm−1, 2160 cm−1, and 2264 cm−1 in the biologically Raman-silent region, respectively. Ultimately, a detection range of 1–50 nM for acetamiprid, atrazine and malathion was achieved with detection limits of 0.39, 0.57 and 0.16 nM, respectively. The developed aptasensors were successfully used to determine pesticide residues in real samples. These proposed multicolor aptasensors offer an effective strategy for pesticide multiresidue detection with advantages of anti-interference, high specificity and high sensitivity.

Dinitrogen Binding and Functionalization from a Low-Coordinate Alkynyliron Complex

Alkynyl complexes of low-coordinate transition metals offer a sterically open environment and interesting bonding opportunities. Here, we explore the capacity of iron(I) alkynyl complexes to bind N2 and isolate a N2 complex including its X-ray crystal structure. Silylation of the N2 complex gives an isolable, formally iron(IV) complex with a disilylhydrazido(2−) ligand, but natural bond orbital analysis indicates that an iron(II) formulation is preferable. The structure of this compound is similar to an earlier reported phenyl complex in which phenyl migration forms a new N–C bond, but the alkynyl group does not migrate. DFT calculations are used to test the possible reasons why the alkynyl is resistant to migration, and these show that the large Fe–C bond energy in the alkynyl complex is a factor that could contribute to the lack of migration.

Acid/Base-driven visualized molecular hinge for advanced information encryption

Dynamically stimuli-responsive fluorescent switches possessing multiple optical outputs provide a promising opportunity for high-level security encryption. Herein, we take the advantage of reversible transformation based on molecular machines to construct an artificial molecular hinge utilizing pyridine, and phenyl and alkynyl groups as the building blocks to establish the hinge wings and rigid axis, respectively. The reversible rotary motion of the molecular hinge can be conveniently regulated, accompanied by multicolor fluorescence changes from the blue to yellow–red region, including white light emission through finely manipulating the protonation-deprotonation processes of the pyridine wing. Based on the multicolor fluorescence characteristic, the information-encrypted materials are conceived as pattern codes that can be quickly and accurately identified by smartphone. Importantly, the temporal feature endows the molecular hinge with time-dependent characteristic, thus pattern codes have been achieved for multi-information storage and information correction. The present work provides a design rationale for better understanding of the relationship between molecular structure, molecular motion and tunable optical properties and paves a way towards constructing advanced encryption materials with higher security requirements.

"Cage Walking" Synthetic Strategy for Unusual Unsymmetrical Supramolecular Cages.

Developing novel assembly methods for supramolecular compounds has long been a research challenge. Herein, we describe how to integrate the B-C coupling reaction and "cage walking" process into coordination self-assembly to construct supramolecular cages. In this strategy, dipyridine linkers containing alkynes react with the metallized carborane backbone through B-C coupling and then "cage walking" resulting in metallacages. However, dipyridine linkers without alkynyl groups can form only metallacycles. We can regulate the size of metallacages based on the length of the alkynyl bipyridine linkers. When tridentate-pyridine linkers participate in this reaction, a new type of ravel is formed. The metallization of carboranes, the B-C coupling reaction, and especially the "cage walking" process of carborane cages play a vital role in this reaction. This work provides a promising principle for the synthesis of metallacages and opens up a novel opportunity in the supramolecular field.