Showing papers on "Pyran published in 2022"

Rh(iii)-catalyzed synthesis of dibenzo[b,d]pyran-6-ones from aryl ketone O-acetyl oximes and quinones via C–H activation and C–C bond cleavage

Abstract: A redox-neutral synthesis of dibenzo[b,d]pyran-6-ones from aryl ketone O-acetyl oximes and quinones has been realized via Rh(iii)-catalyzed cascade C–H activation annulation. A possible Rh(iii)–Rh(v)–Rh(iii) mechanism involving an unprecedented β-C elimination step was proposed.

Chitosan-EDTA-Cellulose network as a green, recyclable and multifunctional biopolymeric organocatalyst for the one-pot synthesis of 2-amino-4H-pyran derivatives

Abstract: Abstract In this research, cellulose grafted to chitosan by EDTA (Cs-EDTA-Cell) bio-based material is reported and characterized by a series of various methods and techniques such as FTIR, DRS-UV–Vis, TGA, FESEM, XRD and EDX analysis. In fact, the Cs-EDTA-Cell network is more thermally stable than pristine cellulose or chitosan. There is a plenty of both acidic and basic sites on the surface of this bio-based and biodegradable network, as a multifunctional organocatalyst, to proceed three-component synthesis of 2-amino-4 H -pyran derivatives at room temperature in EtOH. The Cs-EDTA-Cell nanocatalyst can be easily recovered from the reaction mixture by using filtration and reused for at least five times without significant decrease in its catalytic activity. In general, the Cs-EDTA-Cell network, as a heterogeneous catalyst, demonstrated excellent catalytic activity in an environmentally-benign solvent to afford desired products in short reaction times and required simple experimental and work-up procedure compared to many protocols using similar catalytic systems.

Sonochemistry in an organocatalytic domino reaction: an expedient multicomponent access to structurally functionalized dihydropyrano[3,2-b]pyrans, spiro-pyrano[3,2-b]pyrans, and spiro-indenoquinoxaline-pyranopyrans under ambient conditions

Abstract: A highly convenient and sustainable one-pot approach for the diversely-oriented synthesis of a variety of medicinally privileged amino-substituted 4,8-dihydropyrano[3,2-b]pyran-3-carbonitriles, and spiro[indoline-3,4′-pyrano[3,2-b]pyran]-3-carbonitrile/carboxylate derivatives on the basis of a domino three-component reaction of readily available carbonyl compounds including aryl aldehydes or isatins, active methylene compounds, and kojic acid as a Michael donor using secondary amine catalyst l-proline under ultrasound irradiation in aqueous ethanolic solution at ambient temperature has been developed. This methodology can involve the assembly of C–C, C C, C–O, C–N bonds via a one-pot operation, and following this protocol, a series of novel amino-substituted spiro[indeno[1,2-b]quinoxaline-11,4-pyrano[3,2-b]pyran]-3-carbonitrile/carboxylates have been synthesized. The practical utility of this method was found to be very efficient for scale-up reaction and other useful transformations. The methodology provides significant advantages including mild reaction conditions, energy-efficiency, short reaction time, fast reaction, simple work-up procedure, broad functional group tolerances, utilization of reusable catalyst, green solvent system, being metal-free, ligand-free, waste-free, inexpensive, etc. Excellent chemical yields have been achieved without using column chromatography. To address the issues of green and more sustainable chemistry, several metrics including Atom Economy (AE), Reaction Mass Efficiency (RME), Atom efficiency, E-factor, Process Mass Intensity (PMI), and Carbon Efficiency (CE) have been quantified for the present methodology that indicates the greenness of the present protocol.

Recent advancements in the multicomponent synthesis of heterocycles integrated with a pyrano[2,3-d]pyrimidine core

Abstract: Heterocyclic compounds incorporated with a pyranopyrimidine skeleton have received substantial consideration owing to their privileged, and intelligible biodiversity. Accordingly, this review highlights the multicomponent synthetic routes adopted to prepare heterocyclic compounds incorporated with the pyrano[2,3-d]pyrimidine skeleton in the preceding two years. The different sections comprise the synthesis of bicyclic, tricyclic, polycyclic, and spirocyclic systems along with the estimation of the probable mechanistic routes for the reaction pathways. Commonly, the pyran ring closure was the major idea of most studies, and the mechanistic pathways of these reactions involved Knoevenagel condensation, Michael addition, and intramolecular cyclocondensation. Besides, the significant biological potency of the compounds recently synthesized from multicomponent reactions is deliberated.

Design of High-Contrast Mechanochromic Materials Based on Aggregation-Induced Emissive Pyran Derivatives Guided by Polymorph Predictions

Abstract: Open AccessCCS ChemistryRESEARCH ARTICLE1 Mar 2022Design of High-Contrast Mechanochromic Materials Based on Aggregation-Induced Emissive Pyran Derivatives Guided by Polymorph Predictions Wen Wang, Ruohan Li, Shuzhang Xiao, Qilin Xing, Xia Yan, Jiayu Zhang, Xinghong Zhang, Haichuang Lan and Tao Yi Wen Wang College of Biological and Pharmaceutical Sciences, China Three Gorges University, Hubei, Yichang 443002 Google Scholar More articles by this author , Ruohan Li Department of Chemistry, Fudan University, Shanghai 200438 Google Scholar More articles by this author , Shuzhang Xiao *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] College of Biological and Pharmaceutical Sciences, China Three Gorges University, Hubei, Yichang 443002 Google Scholar More articles by this author , Qilin Xing College of Biological and Pharmaceutical Sciences, China Three Gorges University, Hubei, Yichang 443002 Google Scholar More articles by this author , Xia Yan College of Biological and Pharmaceutical Sciences, China Three Gorges University, Hubei, Yichang 443002 Google Scholar More articles by this author , Jiayu Zhang College of Biological and Pharmaceutical Sciences, China Three Gorges University, Hubei, Yichang 443002 Google Scholar More articles by this author , Xinghong Zhang College of Biological and Pharmaceutical Sciences, China Three Gorges University, Hubei, Yichang 443002 Google Scholar More articles by this author , Haichuang Lan College of Biological and Pharmaceutical Sciences, China Three Gorges University, Hubei, Yichang 443002 Google Scholar More articles by this author and Tao Yi *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] Department of Chemistry, Fudan University, Shanghai 200438 State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Chemistry, Chemical Engineering and Biotechnology, Donghua University, Shanghai 201620 Google Scholar More articles by this author https://doi.org/10.31635/ccschem.021.202100885 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail High-contrast mechanochromic (MC) materials are prominent candidates for sensor, security, and memory applications; however, the development of materials with a large luminescence change (Δλem > 100 nm) under external stimuli is challenging. Considering that polymorphic molecules usually exhibit reversible mechanochromism, polymorph prediction is adopted for the first time to guide the design of high-contrast MC materials in this study. We designed and synthesized a series of donor–π–acceptor pyran derivatives bearing different electron donors and acceptors as model systems. The polymorph prediction indicated that 4-dicyanomethylene-2,6-distyryl-4H-pyran and 4H-pyran-4-one derivatives had the potential to crystallize in both monomer and π-dimer aggregates, while barbituric acid-based compound tended to pack tightly in all aggregated states. The experimental results agreed well with the prediction that the derivatives potentially possessing both monomer and π-dimer aggregate structures exhibit excellent MC behavior, whereas the fluorescence difference for the barbituric acid-based compounds is minimal. Moreover, a compound with an excellent fluorescence difference of three colors during reversible mechanochromism was chosen as the candidate for an optical recording material and security ink. This work proposes an effective method to guide the design of stimuli-responsive materials, which may open promising avenues for the development of high-contrast MC molecules. Download figure Download PowerPoint Introduction The development of stimuli-responsive organic fluorescent materials has received tremendous attention as a result of their fundamental research and promising applications in information storage,1,2 anti-counterfeiting paper,3,4 sensors,5–7 and bioimaging.8–10 In particular, mechanochromic (MC) materials that use mechanical force as a stimulus have been recognized as ideal candidates for preparing anti-counterfeiting labels and pressure-sensitive devices.11–13 Compared with inorganic MC materials, organic MC materials have a number of key advantages, such as abundant synthetic techniques, low preparation costs, and functional diversity. A large number of organic MC materials have been developed based on their conversion between different conformations or molecular packing styles. However, most of these materials exhibit a small emission difference upon grinding and low sensitivity to mechanical force, which limits their practical applications. Currently, the design of high-contrast organic MC materials with large emission wavelength differences remains a significant challenge. Theoretically, the luminescence change during mechanochromism is the result of stimuli-induced transitions between different conformations or molecular packings.14,15 Therefore, organic molecules with multiple polymorphs are usually MC because their molecular packing or conformations are interchangeable under external stimuli.16–20 For example, the phenothiazine unit in a D–π–A compound can exhibit both quasi-axial and -equatorial conformations that emit local excited emission (LE) or intramolecular charge-transfer (ICT) fluorescence, and these two conformations can be converted to each other by external stimuli.21,22 As for planar fluorescent molecules, cyano-substituted oligo(p-phenylenevinylene) derivatives can form monomers and excimers under different stimuli, therefore making them high-contrast multicolored MC materials.23,24 In some cases, both the conformation and molecular packing might change under various stimuli.25–27 Therefore, questions arise regarding which kind of molecule has the potential to aggregate in both monomer (namely without intermolecular π–π interaction) and π-dimer (with strong π–π interaction between neighboring molecules) and what kind of molecule can comprise conformations with a significant difference? If we can calculate the potential polymorphs of the designed molecules, we might be able to predict their MC behavior. In fact, crystal structure prediction has been proven successful in many cases, based on the minimization of the crystal lattice energy. With polymorphs being identified as local minima of relatively low energy, the general framework encompasses a number of crystal structure prediction methods, such as Accelrys Cerius2 modeling, GRACE, MOLPAK, UPACK, and so on.28,29 Using these prediction methods, we might be able to calculate the potential crystal structures of designed molecules and then identify their luminescence differences between different crystalline states. Herein, we propose the prediction of the potential molecular packings of organic D–π–A molecules to guide the design of MC molecules. Considering that intense emission in the solid state is important for a MC molecule, solid emissive materials with a planar π system are chosen as the candidates. Normally, planar chromophores favor strong intermolecular π–π stacking to quench the emission in the solid state30; fortunately, the fluorescence-quenching problem can be overcome by introducing aggregation-induced emission (AIE) groups to restrict intramolecular rotation in the aggregate state.31–34 Pyran derivatives bearing a strong electron acceptor, such as carbonyl,35 cyano,36–38 or indene-1,3-dione groups,39,40 are planar in chemical structure but AIE active. Therefore, we designed a series of pyran derivatives bearing different substituted electron donors and acceptors (Figure 1a). According to the polymorph prediction, 4-dicyanomethylene-2,6-distyryl-4H-pyran and 4H-pyran-4-one derivatives have the potential to crystallize in both monomer and π dimer aggregates, resulting in different emissions. In comparison, barbituric acid-based compounds tended to pack tightly in all aggregated states with intermolecular π–π stackings present in all predicted structures. Our experimental results revealed that different emissive aggregates with significant emission differences (Δλem > 75 nm) were obtained for all the 4-dicyanomethylene-2,6-distyryl-4H-pyran and 4H-pyran-4-one derivatives, whereas only a 20 nm wavelength shift was observed for the barbituric acid-based compounds, in agreement with the results from the polymorph prediction. As far as we know, this is the first report of computation-guided design of MC molecules, which may open promising avenues for the development of high-contrast MC molecules with remarkable MC luminescence. Figure 1 | (a) Chemical structures of designed molecules; (b–g) predicted molecular packing with the most and least intense intermolecular π–π interactions: (b) 1-Ph, (c) 2-Ph, (d) 3-Ph, (e) 3-PhF, (f) 3-PhCl, and (g) 3-Np (π-dimer: two molecules completely overlapped; monomer: almost no molecule overlapping; cross overlapped: two molecules overlap partially in different directions; half-overlapped: two molecules overlap along one side). Download figure Download PowerPoint Experimental Methods Measurement Nuclear magnetic resonance (NMR) spectra were recorded on a Bruker 400 NMR spectrometer. Chemical shifts were reported in ppm with tetramethylsilane as reference. Mass data were recorded on an Applied Biosystems Voyager-DE STR mass spectrometer. UV–vis and fluorescence spectra measurements were carried out on a Shimadzu UV-2600 and a Hitachi F-4600 spectrometers, respectively. The fluorescence quantum yields and fluorescence lifetime measurements of the solid powder were performed on an Edinburgh FS5 luminescence spectrometer with 450 nm excitation source. Powder X-ray diffraction (PXRD) patterns were measured on a Bruker Advance D8 X-ray diffractometer in the 2θ range from 5° to 50°. Single-crystal X-ray diffraction data were collected on a Rigaku XtaLAB PRO single-crystal X-ray diffractometer equipped with a graphite monochromated Cu Kα radiation (λ = 1.54184 Å) at 298 K. The single crystals of 3-Ph and 3-PhCl were cultured from slow evaporation of organic solvents and their CCDC numbers are 2023435 and 2039964, respectively. Electrochemical studies were carried out with a conventional three-electrode system using an AUTOLAB electrochemical work station (PGSTAT12) in deoxygenated and anhydrous N,N-dimethylformamide at room temperature. The potentials were reported versus ferrocene as the internal standard with a scan rate of 100 mV s−1, using a glassy carbon working electrode, Pt flake counter electrode, and saturated calomel electrode (SCE) as the reference electrode. The sample solutions contained 5.0 × 10−3 M as the prepared compound and 0.1 M tetrabutylammonium hexafluorophosphate (Bu4NPF6) as a supporting electrolyte. Nitrogen was bubbled for 10 min before each measurement. Sample preparation for MC study The synthesis and characterizations of designed compounds were depicted in ESI ( Supporting Information Figures S12–S21). The initial powdered sample was obtained by vacuum evaporation of the column eluents or recrystallization. The initial state of 1-Ph was obtained by recrystallization from ethanol; 2-Ph was obtained by precipitation from a hot dimethyl sulfoxide (DMSO) solution upon cooling; 3-Ph was obtained by recrystallization from chloroform; 3-PhF and 3-PhCl were obtained by recrystallization from tetrahydrofuran (THF); 3-Np was obtained by precipitation from a hot acetonitrile solution upon cooling. The ground samples were prepared by grinding the initial powders in a mortar with a pestle. The fumed samples were acquired by fuming the ground powders with organic solvents for 15 min, and the annealed samples were obtained by heating the ground powders in a hot-stage with an automatic temperature-control system at 120 °C for 10 min and subsequently cooled to room temperature. Computational methods Geometry-optimized molecular structures computed by density functional theory (DFT) are used as inputs to the polymorph predictions. In the DFT study, we applied B3LYP with 6-31G(d,p) basis sets for the designed compounds. The search for potential structures was initially restricted to the ten most prevalent space groups (P21/c, P-1, P212121, P21, C2/c, Pbca, C2, Pna21, Pbcn, and Cc), using the simulated annealing algorithm of Karfunkel and Gdanitz as implemented in the Accelrys Polymorph Predictor module of the Materials Studio software.41 The final energy minimizations were performed using the Dreiding force field. Molecular packing in the calculated structures was analyzed by Mercury. The molecular cluster with the most intense intermolecular π–π interactions was chosen as the input and calculated at the M06-2X/6-31G(d,p) level with dispersion correction (Empirical dispersion = GD3). Then intermolecular interactions were analyzed by Multiwfn.42 Results and Discussion The potential molecular packing of the designed compounds was restricted to the 10 most prevalent space groups, using the simulated annealing algorithm of Karfunkel and Gdanitz as implemented in the Accelrys Polymorph Predictor. For a planar molecule in the aggregate state, the intermolecular π–π interactions usually determine its fluorescence properties. Therefore, the molecular clusters with the most intense intermolecular π–π interactions were extracted from the predicted crystal structures and analyzed and visualized as a “green cloud.” If there is no planar overlapping in the predicted crystal structure, the clusters with other supramolecular forces were extracted and analyzed, and the negligible “ground cloud” was identified as weak intermolecular interactions, such as hydrogen bonding. The predicted details, including space groups, optimized packing styles, and the energy of the designed molecules, are shown in Supporting Information Tables S1–S6. The predicted clusters with the most and least intense intermolecular π–π stacking were extracted, as shown in Figures 1b–g. According to the polymorph prediction, both clusters with intense or no intermolecular π–π stacking were found in the predicted crystal structures of the pyran-4-one and dicyanomethylene-4H-pyran derivatives (namely, 1-Ph, 3-Ph, 3-PhF, 3-PhCl, and 3-Np), indicating that all these five compounds have the potential to form both π-dimer and monomer forms in the aggregate states. Therefore, they should be able to crystallize in different polymorphs and emit different fluorescence. In particular, a half-overlapped dimer was found in the polymorphs of 3-PhCl, indicating that 3-PhCl might be able to provide multicolored states (e.g., monomer, half-dimer, and π-dimer). Thus, the different emissive states of these five compounds should be observed and converted into each other under external stimuli, exhibiting high-contrast chromic properties. In comparison, 2-Ph with 1,3-dimethylbarbituric acid as an electron acceptor only tended to aggregate as π-dimers or partial-overlapping clusters in all polymorphs, with no monomer state found. These results revealed that the fluorescence of 2-Ph should be less active with external stimuli, unlike the other five compounds, which can form aggregates with significant differences. The designed compounds were facilely synthesized through typical nucleophilic addition reactions. Nucleophilic addition between commercially available 2,6-dimethyl-γ-pyrone and benzaldehyde gave 1-Ph directly.35 Condensation of 2,6-dimethyl-γ-pyrone with electron-withdrawing groups (malononitrile or 1,3-dimethylbarbituric acid), followed by condensation with different aromatic aldehydes, provided other target products with yields from 40% to 78%.36–38 All synthesized compounds were well-characterized. To verify the predicted results, we cultivated single-crystal structures using a slow evaporation method with different organic solvents. Finally, single crystals of 3-Ph and 3-PhCl suitable for X-ray single-crystal diffraction were obtained from mixed solvents (dichloromethane/acetonitrile 1∶1 for 3-Ph and acetone/THF 1∶4 for 3-PhCl). The 3-Ph crystallizes in an orthorhombic structure with space group P212121, similar to the reported structure ( Supporting Information Table S9).36 The main conjugated system exhibited good planarity, except that one terminal phenyl ring was slightly twisted from the plane with a dihedral angle of 17.0° (Figure 2a). Due to the planar character of the molecule, planar overlapping with a neighboring molecule was facilitated, thereby providing a π–π stacked dimer. The π-distance between two molecules was measured to be 3.39 Å, manifested in strong face-to-face intermolecular π–π interactions. However, only one side of the molecule overlapped with a neighboring molecule and the intermolecular π–π interaction on the other side was limited. As a result, the crystal emitted a red aggregate emission centered at 599 nm (Figure 2b). Among the 10 predicted crystal structures, six adopted this kind of packing but with different overlapping degrees, indicating that it was the predominant molecular stacking mode for 3-Ph ( Supporting Information Table S3). Figure 2 | (a and c) Conformation and intermolecular π–π interactions 3-Ph and 3-PhCl, respectively; (b and d) fluorescent spectra and dark field images of single crystals of 3-Ph and 3-PhCl, respectively. Download figure Download PowerPoint In comparison, 3-PhCl crystallized as a triclinic crystal in space group P-1 with one THF molecule in the crystal that adopted a highly planar conformation (Figure 2c). Theoretically, this high planarity promotes intermolecular π–π stacking; however, only half of the molecule overlaps with a neighboring molecule in the crystal structure. The π distance between two molecules was measured to be 3.4 Å, almost the same as that in 3-Ph. Although 3-PhCl comprised higher planarity compared with 3-Ph, the crystal of 3-PhCl emitted a shorter wavelength fluorescence with a broader band (orange fluorescence centered at 595 nm) (Figure 2d), which could be ascribed to its reduced overlapping degree in the cluster. This molecular packing matched the half-overlapped one of the predicted crystal structure very well (Figure 1f). According to DFT calculations, all these pyran derivatives comprised typical D–π–A structures and a planar conformation ( Supporting Information Figure S1). Values of the electronic states (highest occupied molecular orbital (HOMO)/lowest unoccupied molecular orbital (LUMO) levels) and energy gaps of the six compounds were calculated by both UV–vis spectra and cyclic voltammetry (CV) curves ( Supporting Information Figure S2 and Table S7). The data calculated by CV curves match well with the results from UV absorption spectra. With stronger electron-withdrawing groups (barbituric acid and malononitrile), obvious red shifts of the absorption wavelength and fine structures were found (Figures 3a and 3b). Since the naphthalene unit is a stronger electron donor compared with phenyl, 3-Np absorbed at a lower energy frequency than 3-Ph. However, the halogen effect was insignificant on their absorptions, and the absorption bands were almost independent of the solvent polarity ( Supporting Information Figures S3–S8). These pyran derivatives emitted poor fluorescence in dilute solutions, which could barely be observed by the naked eye under 365 nm light irradiation. Figure 3 | (a) Absorption and (b) normalized fluorescence spectra of pyran derivatives in acetonitrile (1.0 × 10−5 M), λex: 320 nm for 1-Ph; 400 nm for 3-Ph, 3-PhF, and 3-PhCl; 420 nm for 2-Ph and 3-Np. Download figure Download PowerPoint Although all pyran derivatives emitted faint fluorescence in dilute solutions, intense emissions could be observed from the solids obtained from column chromatography, indicating their AIE behavior. Thus, the AIE properties of these compounds were studied in detail by the addition of water to their acetonitrile solutions. All these pyran derivatives exhibited higher fluorescence intensity with red-shifted wavelengths when water was added to the acetonitrile solution to provide aggregated particles (Figure 4). The suspended aggregates in the mixed solvent were confirmed by the Tyndall effect ( Supporting Information Figure S9). Among the compounds with phenyl rings as electron donors, 3-Ph bearing malononitrile as an acceptor emitted the most intense fluorescence in the aggregate state (Figure 4). The introduction of halogen atoms or larger aromatic rings results in decreasing fluorescence intensity when a large amount of water was added, indicating that the increased π-conjugated system intensified the intermolecular π–π interaction to decrease the fluorescence efficiency in the aggregate state. Moreover, a red shift was also observed in the absorption of these pyran compounds during aggregation ( Supporting Information Figure S10). Figure 4 | Fluorescent spectra changes of the designed compounds in acetonitrile/H2O mixture with fw = 0–99%. The insets show the relative fluorescent intensity (I/I0) change and fluorescent images with different fw under 365 nm light irradiation (1.0 × 10−5 M). Download figure Download PowerPoint Because the designed compounds have multipolymorph potential and AIE properties, their solids may exhibit the expected MC properties. A previous study showed that the fluorescent wavelength of 1-Ph underwent almost no change during the MC process.35 However, according to the polymorph prediction, 1-Ph should be able to crystallize in both π-dimer and monomer forms, resulting in different emissive solids. To verify these predictions, the MC behavior of 1-Ph was reinvestigated. The sample crystallized from ethanol gave a faint emission with a predominant peak at 422 nm with a shoulder at 470 nm (Figure 5a). The fluorescence decay time of the 1-Ph powder was 0.30, 2.64 ns (88/12%) ( Supporting Information Table S8), ascribed to the monomer and π–π stacked species. Upon grinding, its emission was significantly enhanced and red shifted to 499 nm (green emission) with the fluorescence decay time increased to 0.98, 3.54 ns (40/60%), indicating that intermolecular π–π interaction got intensified. It is noteworthy that the grinding powder was still crystalline with a decrease in the diffraction intensity and the appearance of two new small peaks at 23.1° and 25.8° (Figure 6). These new peaks might represent the existence of intermolecular π–π interactions with d spaces of 3.44 and 3.84 Å, respectively, which induced red shift of the fluorescence and extension of the fluorescence decay time ( Supporting Information Table S8). Upon annealing or fuming with ethanol, the diffractions become sharp again, but the peaks ascribed to π–π stacking did not disappear, indicating that fuming and thermal treatment could not completely restore its initial state. Figure 5 | Fluorescent spectra and images of the pyran derivatives under external stimuli. (a) 1-Ph; (b) 2-Ph; (c) 3-Ph; (d) 3-PhF; (e) 3-PhCl; (f) 3-Np. Download figure Download PowerPoint Among the potential aggregation states of 2-Ph, intermolecular π–π interactions are always present according to the prediction. The crystallized solids of 2-Ph from common organic solvents (e.g., dichloromethane, chloroform, ethyl acetate, THF, acetonitrile, methanol, and ethanol) emitted red fluorescence with wavelengths from 600 to 626 nm ( Supporting Information Figure S11), obviously red shifted compared with their dilute solutions (below 515 nm), indicating the presence of intermolecular π–π interactions in the solids. In the XRD pattern of 2-Ph, a strong diffraction peak appeared at 2θ 26.7° (d-spacing of 3.33 Å) (Figure 6), manifesting strong intermolecular π–π stacking. Upon grinding, this peak is still present, but broadened. After fuming or annealing, the diffractions become sharper. Clearly, intermolecular π–π interactions were present in all the aggregate states of 2-Ph during the MC process (5b), which agreed well with the polymorph prediction. Figure 6 | PXRD patterns of all samples during the MC process. Download figure Download PowerPoint Although 3-Ph has long been known to be AIE active, none of its stimuli-responsive properties have been surveyed.36 In fact, the solid powder of 3-Ph obtained by evaporation of the eluents from column was orange in emission, and no obvious fluorescence change was observed after grinding. However, the crystalline sample by recrystallization from chloroform emitted yellow fluorescence centered at 553 nm. Because the π dimer with half-overlapping in the single crystal of 3-Ph exhibited a broad emission band centered at 599 nm, the emission at 553 nm could be ascribed to the monomer. After grinding, a new band at about 616 nm arose and was further red shifted to 636 nm through fuming by dichloromethane, indicating the gradually enhanced intermolecular π–π stacking. Interestingly, the thermal treatment gave an orange emissive sample with two emissive bands located at 599 and 633 nm (5c). These results suggested that the aggregate states of 3-Ph comprised different molecular packings, imparting them with more than one emission peak, in accordance with their XRD patterns because multiple diffractions were found in all the samples. The halogen effect has been proven essential for adjusting the supramolecular self-assembly of organic fluorescent materials.43–45 Although the introduction of halogen atoms did not affect the photophysical properties of the molecules in dilute solutions, the potential halogen bonding might impart unique molecular packings and photoluminescent properties. The initial solid powder of 3-PhF obtained by recrystallization from THF exhibited a broad emission band centered at 552 nm with a shoulder band at ∼640 nm. After grinding in a mortar to turn the crystalline powder amorphous, a red emission centered at 645 nm was observed (5d). Fuming or thermal force provided a sample with dual emissions at 550 and 645 nm, clearly representing the existence of both monomer and π-dimer emissions. In comparison, when the fluoro group was replaced by a chloro group, the initial sample of 3-PhCl obtained by recrystallization from THF emitted at 578 nm slightly blue shifted from that of the single crystal with the half-overlapping cluster (595 nm). Because strong diffractions at 26.6° and 27.0° representing π–π stacking were observed in its XRD patterns, the orange emission of 3-PhCl was ascribed to the half-dimer. Upon grinding, an obvious red shift was observed and the fluorescence moved to 653 nm (5e). However, the deep-red emission could be converted into the yellow color of the monomer emission (centered at 550 nm with a comparatively narrower band) after annealing. Therefore, tricolor states with significant differences were obtained for 3-PhCl, which agreed well with the polymorph prediction. The arene effect also plays an important role in the supramolecular self-assembly because the electronic environments in different arene units result in various intermolecular π–π interactions.46 When naphthalene units were introduced to the skeleton instead of phenyl rings, 3-Np was expected to form both monomers and π-dimers with different emissions according to the polymorph prediction. In fact, the MC property of 3-Np has been reported previously, but only a 24 nm difference in its emission wavelength was observed during the MC process,37 which is inconsistent with the polymorph prediction. Therefore, the MC property was reinvestigated carefully. The initial powder obtained by recrystallization from acetonitrile emits at 564 nm. After grinding heavily in a mortar to become amorphous, a significant red shift (Δλem = 100 nm) was observed (5f). Finally, a deep-red emissive powder ascribed to the intensified intermolecular π–π stacking was obtained. After fuming with dichloromethane or annealing, new crystalline emitting the same yellow fluorescence as the initial state was obtained. The conversion between yellow and deep-red fluorescence could be ascribed to the transition from monomer to π-dimer aggregate. Among the five compounds with large fluorescence differences during mechanochromism, three colors with obvious differences were obtained for 3-PhCl. Therefore, 3-PhCl was chosen as the candidate for application as an optical recording material and security ink. First, a piece of brown paper was immersed in a THF solution of 3-PhCl. After drying i

Synthesis and Biological Activity of Functionally Substituted Pyrimidine and Pyran Derivatives on the Basis of Isatylidene Malononitriles

Abstract: In this study, it was shown that pyrimidine and imidazopyridine derivatives were obtained from the multicomponent reaction of isatylidene malononitriles with malononitrile and diamines at room temperature. Also, novel complexes effectively inhibited AChE enzyme, with Ki values in the range of 4.56 to 8.21 μM. For this enzyme, it was obtained with IC50 values in the range of 4.04 to 9.85 μM. For α-glycosidase enzyme the most effective Ki values were for 4 a and 10 compounds with Ki values of 31.48 and 32.63 μM, respectively. On the other hand, molecular docking studied for best inhibitors.

Anticonvulsant activity, molecular modeling and synthesis of spirooxindole-4H-pyran derivatives using a novel reusable organocatalyst

Abstract: Fifteen derivatives of spirooxindole-4H-pyran (A1-A15) were subjected to evaluate through intravenous infusion of pentylenetetrazole (PTZ)-induced epilepsy mouse models. Four doses of the compounds (20, 40, 60 and 80 mg/kg) were tested in comparison with diazepam as positive control. The resulted revealed that compounds A3 and A12 were the most active compounds and indicated significant anticonvulsant activity in the PTZ test. The tested compounds were prepared via a multicomponent reaction using graphene oxide (GO) based on the 1-(2-aminoethyl) piperazine as a novel heterogeneous organocatalyst. The prepared catalyst (GO-A.P.) was characterized using some diverse microscopic and spectroscopic procedures as well. The results showed high catalytic activity of the catalyst in the synthesis of spirooxindole-4H-pyran derivatives. The GO-A.P. catalyst was reusable at least for 5 times with no significant decrease in its catalytic action. In silico assessment of physicochemical activity of all compounds also were done which represented appropriate properties. Finally, molecular docking study was performed to achieve their binding affinities as γ-aminobutyric acid-A (GABA-A) receptor agonists as a plausible mechanism of their anticonvulsant action. Binding free energy values of the compounds represented strongly matched with biological activity.

A New Pathway for the Preparation of Pyrano[2,3-c]pyrazoles and molecular Docking as Inhibitors of p38 MAP Kinase

Abstract: We report a new pathway to synthesize pyrano[2,3-c]pyrazoles and their binding mode to p38 MAP kinase. Pyrano[2,3-c]pyrazole derivatives have been prepared through a four-component reaction of benzyl alcohols, ethyl acetoacetate, phenylhydrazine, and malononitrile in the presence of sulfonated amorphous carbon and eosin Y as catalysts. All products were characterized by melting point, 1H and 13C NMR, and HRMS (ESI). The products were screened in silico for their binding activities to both the ATP-binding pocket and the lipid-binding pocket of p38 MAP kinase, using a structure-based flexible docking provided by the engine ADFR. The results showed that eight synthesized compounds had a higher affinity to the lipid pocket than to the other target site, which implied potential applications as allosteric inhibitors. Finally, the most biologically active compound, 5, had a binding affinity comparable to those of other proven lipid pocket inhibitors, with affinity to the target pocket reaching −10.9932 kcal/mol, and also had the best binding affinity to the ATP-binding pockets in all of our products. Thus, our research provides a novel pathway for synthesizing pyrano[2,3-c]pyrazoles and bioinformatic evidence for their biological capability to block p38 MAP kinase pockets, which could be useful for developing cancer or immune drugs.

Tandem Macrolactone Synthesis: Total Synthesis of (-)-Exiguolide by a Macrocyclization/Transannular Pyran Cyclization Strategy.

Abstract: Tetrahydropyran-containing macrolactones were synthesized by integrating Meyer-Schuster rearrangement, macrocyclic ring-closing metathesis, and transannular oxa-Michael addition under gold and ruthenium catalysis. Single-step access to a variety of 14- to 20-membered macrolactones containing a tetrahydropyran ring was possible from readily available linear precursors in good yields and with moderate to excellent diastereoselectivity. A 13-step synthesis of (-)-exiguolide, an anticancer marine macrolide, showcased the feasibility of our domino reaction sequence for macrolactone synthesis and also demonstrated the power of transannular reactions for rapid assembly of the tetrahydropyran rings of the target natural product.

Progress of Dicyanomethylene-4H-Pyran Derivatives in Biological Sensing Based on ICT Effect

Abstract: As one of the typical fluorescent cores, dicyanomethylene-4H-pyran (DCM) derivatives exhibit excellent photophysical and photochemical properties, such as large Stokes shift, excellent light stability, and tunable near-infrared (NIR) emission. The luminescence mechanism of DCM probes mainly depends on the intramolecular charge transfer (ICT). Hence, by regulating the ICT process, the probes can specifically act on the target molecule. Accordingly, a series of NIR DCM probes have been constructed to detect the ions, reactive oxygen species (ROS), and biological macromolecules in cells. However, there is no relevant review to summarize it at present. This minireview mainly summarizes the NIR DCM probes based on ICT effect and their applications in biosensors and biological imaging in recent years. This will be beneficial to innovatively construct new DCM probes and actively promote their application in the future.

Molecular optimization of incorporating pyran fused acceptor–donor–acceptor type acceptors enables over 15% efficiency in organic solar cells

Abstract: Three acceptor–donor–acceptor type fused-ring non-fullerene acceptors of FOR-IN , FOR-1F and FOR-2F , were synthesized with the same pyran-composed backbone but different terminals, affording over 15% efficiency in organic solar cells.

Fabrication of self-assembled Co3O4 nano-flake for one-pot synthesis of tetrahydrobenzo[b]pyran and 1,3-benzothazole derivatives

Abstract: We report the fabrication of self-assembled Co3O4 nano-flake material by dissociation of CoCl2.6H2O under basic medium using co-precipitation method. The electronic/crystalline structure and morphology and elemental purity of Co3O4 material have been analyzed by UV–Vis, fluorescence, powder X-ray diffraction, field emission scanning electron microscopy, and energy dispersive X-ray measurement. The Co3O4 nano-flake has demonstrated excellent catalytic activity in the one-pot multicomponent synthesis of tetrahydrobenzo[b]pyran and 2-aryl-1,3-benzothazole derivatives under neat conditions in excellent yields. The Co3O4 nano-flake material was recovered from the reaction mixture and reused for at least ten runs without appreciable loss of catalytic activity.

Synthesis of Pentacyclic Pyran Fused Pyrazolo Benzo[ h ]quinolines by Multicomponent Reaction and Their Photophysical Studies

Abstract: Herein we report for the first time a one-pot method for the synthesis of pentacyclic pyran fused pyrazolo benzo[h]quinolines in acetic acid medium from the three-component reaction of 2-hydroxy-1,4-naphthoquinone, α, β-unsaturated aldehydes and 5-aminopyrazoles under the reflux conditions. In this reaction, four new bonds (2 C−C, 1 C−N and 1 C−O) and two new rings (pyridine and pyran) were formed in one-pot. The novel products contain four bioactive moieties such as pyran, pyridine, pyrazole and α-naphthol. The salient features of this method are: one-pot process, short reaction time, easier purification, no need of column chromatography and good yields of the products. All the products were characterized by IR, NMR and HRMS. Most of our synthesized compounds were found highly fluorescent. Therefore, we further studied their photophysical properties by UV-Visible and Fluorescence spectroscopy. We have calculated their quantum yields which were found in the range 0.243–0.424 in CHCl3 solution (c=10−5 M). Compound 4 e showed the highest quantum yield of 0.424.

Chitosan‐ZnO: An Efficient and Recyclable Polymer Incorporated Hybrid Nanocatalyst to Synthesize Tetrahydrobenzo[ b ]pyrans and Pyrano[2,3‐ d ]pyrimidinonesunder Microwave Expedition

Abstract: The innovation of facile, efficient and mild procedures utilizing contemptible, conveniently separable and reusablesolid catalysts that overcome obstacles are invariably in demand. Hence, a straightforward one-pot multicomponent reaction (MCR) and an expedient procedure for the synthesis of pyran annulated heterocycles 5 a–k and 6 l–v is developed using Chitosan-Zinc oxide (CS-ZnO) hybrid nanocatalyst. Use of aqueous medium is one of the major highlight of the present protocol. This protocol renders ease of operation, facile work up and magnified yields (90–95 %) as well as explores the use of modified polymeric substrates in the organic synthesis.

Multicomponent Electrocatalytic Selective Approach to Unsymmetrical Spiro[furo[3,2-c]pyran-2,5′-pyrimidine] Scaffold under a Column Chromatography-Free Protocol at Room Temperature

Abstract: Electrochemical synthesis suggested a mild, green and atom-efficient route to interesting and useful molecules, thus avoiding harsh chemical oxidizing and reducing agents used in traditional synthetic methods. Organic electrochemistry offers an excellent alternative to conventional methods of organic synthesis and creates a modern tool for carrying out organic synthesis, including cascade and multicomponent ones. In this research, a novel electrocatalytic multicomponent transformation was found: the electrochemical multicomponent assembly of arylaldehydes, N,N′-dimethylbarbituric acid and 4-hydroxy-6-methyl-2H-pyran-2-one in one pot reaction was carried out in alcohols in an undivided cell in the presence of alkali metal halides with the selective formation of substituted unsymmetrical 1′,3′,6-trimethyl-3-aryl-2′H,3H,4H-spiro[furo[3,2-c]pyran-2,5′-pyrimidine]-2′,4,4′,6′(1′H,3′H)-tetraones in 73–82% yields. This new electrocatalytic process is a selective, facile and efficient way to obtain spiro[furo[3,2-c]pyran-2,5′-pyrimidines]. According to screening molecular docking data using a self-made Python script in Flare, all synthesized compounds may be prominent for different medical applications, such as breast cancer, neurodegenerative diseases and treatments connected with urinary tract, bones and the cardiovascular system.

The Crystal Structure of 3-Amino-1-(4-Chlorophenyl)-9-Methoxy-1H-Benzo[f]Chromene-2-Carbonitrile: Antimicrobial Activity and Docking Studies

Abstract: Compound 3-amino-1-(4-chlorophenyl)-9-methoxy-1H-benzo[f]chromene-2-carbonitrile (4), was synthesized via the reaction of 7-methoxynaphthalen-2-ol (1), 4-chlorobenzaldehyde (2), and malononitrile (3) in an ethanolic piperidine solution under microwave irradiation. The synthesized pyran derivative 4 was asserted through spectral data and X-ray diffraction. The molecular structure of compound 4 was established unambiguously through the single crystal X-ray measurements and crystallized in the Triclinic, P-1, a = 8.7171 (4) Å, b = 10.9509 (5) Å, c = 19.5853 (9) Å, α = 78.249 (2)°, β = 89.000 (2)°, γ = 70.054 (2)°, V = 1717.88 (14) Å3, Z = 4. The target molecule has been screened for antibacterial and antifungal functionality. Compound 4 exhibited favorable antimicrobial activities that resembled the reference antimicrobial agents with an IZ range of 16–26 mm. In addition, MIC, MBC, and MFC were assessed and screened for molecule 4, revealing bactericidal and fungicidal effects. Lastly, a molecular docking analysis was addressed and conducted for this desired molecule.