Search

The Diels–Alder reactions of sulfolenodipyrrins prove to be an efficient way to construct aromatic ring-fused dipyrrins. However, adjustable annulation is still hard to achieve. To address this, molecular engineering on the H-bond has been employed. The α-position aryl group-modified sulfolenodipyrrins have been synthesized to react with various dienophiles in Diels–Alder reactions, affording the monoannulation products with different regioselectivity in good yields (45–76%). The remaining sulfolenopyrrole in monoadducts can undergo further fusion in the presence of dienophiles and TEMPO, giving the bisadducts with a lactam subunit in an appropriate yield. According to the crystal structures and theoretical calculations, the intramolecular H-bonds between the α-substituent and the nearby pyrrole confine the conjugation pathway of the dipyrrin core. With respect to the normal NH-sulfolenopyrrole, the imino-type one features low aromaticity, from which SO2extrusion generates more stable dipyrrin-diene, achieving regioselectivity. In addition, aromatic ring fusion results in red-shifted absorption and emission spectra, and the annulation units regulate the emission intensity. This work shows the versatility of intramolecular H-bonds in regulating the reaction through confinement of the conjugation system.

An enantioselective Mannich reaction with cyclic N-sulfonyl ketimines as the nucleophiles was developed. In the presence of 5 mol % chiral thiourea catalyst C11, the asymmetric Mannich reaction between cyclic N-sulfonyl ketimines and isatin-derived ketimines was achieved in high yields and good-to-excellent enantioselectivities (84–99% yields with 75–99.8% ee). This methodology provided an effective route to construct chiral 3-amino-2-oxindoles containing a cyclic N-sulfonyl ketimine scaffold. The initial biological evaluation of the products in cell-based assays demonstrated that some compounds have excellent antiproliferative activity against human osteosarcoma cells.

A catalytic asymmetric vinylogous Mannich-type reaction between β,γ-unsaturated amides and ketimines has been developed in excellent regio-, diastereo-, and enantioselectivities. The methodology provides an efficient approach to construct chiral homoallylic amines with a 3-amino-2-oxindole scaffold. Moreover, the transformations of the chiral products, including the removal of the pyrazole group or Boc group, the reduction of the C–C double bond, and Suzuki coupling, have been investigated.

Sulfolenodipyrrins are employed as building blocks to concisely and efficiently construct aromatic rings (e.g., naphthoquinone, anthraquinone, fullerenes, and phthalimide) from fused dipyrrins by programmed [4 + 2]-cycloaddition reactions. Notably, alkylamino-substitution at the α-position not only enhances the reactivity of sulfolenodipyrrins but also results in the regio-selectivity of the cycloaddition reactions. Theoretical calculations in terms of frontier orbitals of dienes, energy of dienes, steric hindrance, and aromaticity have been conducted to understand the reason in depth. Additionally, the fusion of aromatic groups enables bathochromic absorption with up to ∼130 nm for the monoadducts and to ∼200 nm for the bis-adducts. The phthalimide annulation dipyrrin displays red emission, while the other mono- or bis-adducts do not, owing to the presence of typical acceptors such as quinone analogs or fullerene.

We report a novel rhodium-catalyzed rearrangement involving N-substituted 2-thiopyridones and diazoesters. This reaction proceeds through the rhodium-catalyzed formation of sulfur ylides, followed by a direct C–N bond cleavage to achieve N-to-C 1,4-pyridyl migration. The protocol can be used to construct various thiopyridines possessing tetrasubstituted carbon stereocenters in moderate to excellent yields, which expands the transformation pattern of sulfur ylide intermediates in rearrangement reactions.

Oxidation of thienyl-blocked bilane and pentapyrrane afforded chain length dependent products of the symmetric dimer D1and the thienyloligopyrrin-appended pentaphyrin analogue P2, respectively, with the latter formed by simultaneous dimerization and cyclization. Coordination of D1and P2with Cu(II) afforded di- and monometallic complexes D1-Cu2and P2-Cu, respectively. These compounds exhibit distinct NIR absorption, with the absorption tail of D1-Cu2extended to ca. 1900 nm despite its smaller conjugation framework than that of P2-Cu.

The gram-scale synthesis of 5,6-, 6,7-, and 7,8-chromene/chromane-type aryne precursors and their applications in regioselective transformation to other functional derivatives is reported. Chromene/chromane-type arynes are generated under mild conditions, which can further undergo [2 + 2], [3 + 2], and [4 + 2] cycloaddition reactions, nucleophilic addition reactions, and σ-insertion reactions to produce structurally novel substituted chromenes and chromanes. The excellent regioselectivity of the reaction is facilitated by the oxygen-containing guiding groups at the ortho-position of the triple bond, which can be removed or switched to other functional groups including alkenyl, aryl, heteroaryl, and arylamino groups.

An organocatalytic asymmetric vinylogous Michael/oxa-Michael tandem reaction between β,γ-unsaturated pyrazoleamides and isatin-derived β,γ-unsaturated ketoesters has been developed with excellent regio-, diastereo-, and enantioselectivities. The methodology provides an effective approach to construct enantiomerically pure 3,4′-pyranyl spirooxindole derivatives containing three contiguous chiral centers. Moreover, the transformations of the chiral products, including the removal and reduction of the pyrazole group, have been investigated.

A Regioselectivity-switchable Diels–Alder reaction of arynes and 4-alkenyloxazoles was explored. By regulating the reaction temperature and the polarity of the solvent, the reaction activity of aryne was controlled to selectively react with different favorable reaction sites of 4-alkenyloxazoles, providing naphtho[2,1-d]oxazoles and 1,4-epoxyisoquinolines. Density functional theory (DFT) calculations demonstrated that the Diels–Alder reaction on acyclic dienes site needs more energy than the reaction on cyclic dienes to overcome the potential reaction barrier.

An efficient and convenient cobalt-catalyzed ortho-C(sp2)–H amidation of benzaldehydes employing dioxazolones as the aminating reagent has been developed. The key feature of this protocol is the use of green and economic earth-abundant metals cobalt as the catalyst with the p-chloroaniline as the transient directing group. Further application of our approach was demonstrated by the synthesis of C1r serine protease inhibitor 45and elastase inhibitor 49.

A copper-catalyzed asymmetric Mannich reaction between glycine Schiff bases and ketimines has been developed. This method afforded 2-oxindole-based chiral syn-α,β-diamino acid derivatives in high yields (89–99%) with good to excellent diastereoselectivities (≤98:2 dr) and excellent enantioselectivities (95–99% ee).

The palladium-catalyzed electrochemical C–H bromination of benzamide derivatives under divided cells is developed, in which NH4Br serves as a brominating reagent and electrolyte. The protocol avoids the use of chemical oxidants and provides an alternative method for the synthesis of aryl bromides.

Palladium-catalyzed electrochemical C–H functionalization reactions have emerged as attractive tools for organic synthesis. This process offers an alternative to conventional methods that require harsh chemical oxidants. However, this electrolysis requires divided cells to avoid catalyst deactivation by cathodic reduction. Herein, we report the first example of palladium-catalyzed electrochemical C–H alkylation of arenes using undivided electrochemical cells in water, thereby providing a practical solution for the introduction of alkyl groups into arenes.

The regioselective and enantioselective Cu(II)-catalyzed 1,4-conjugate addition of diethylzinc reagent to nitrodienes is described. With 0.25 mol % of Cu(OAc)2and chiral amidophosphine ligand L3, the 1,4-addition products were produced with a complete regioselectivity, high yields (81–98%), and excellent enantioselectivities (87–97% ee) in a short reaction time.

Iridium-catalyzed asymmetric intermolecular Friedel–Crafts type allylic substitution reaction of anthrones was developed, affording C10 substituted allylanthrones in good to excellent yields, regioselectivity and enantioselectivity.

This paper explores the design of a new type of deployable bridge system composed of a scissor-like deployable element, the walking-slab, the joint, sleeve-pole,cable and lock-device, driving cable etc. Both geometric principles and dynamic analysis are discussed. Then, a 2-m scaled prototype is developed, which was then experimentally tested for dynamic properties. Finally, the results of experiment are in good agreement with the dynamic analysis prediction, which validates the efficiency of the design for the deployable bridge. The primary novelty is scissor-like element of the deployable emergency bridge, which is found to enhance the stiffness of the entire deployable to overcome the natural or artificial barriers.

An efficient method has been developed for the Pd(0)-catalyzed benzylation of indoles, which occurred with exclusive regioselectivity. When this reaction was performed in the presence of Pd(PPh3)4, it provided access to a broad range of substituted indoles bearing diarylmethanes at their 3-position in 90%–99% yields under mild conditions.

TiO2 nanosheets have been successfully synthesized via a simple sol-gel process. These nanostructures were characterized by transmission electron microscopy (TEM) and x-ray energy dispersive spectrometer (EDS). The sheet-shaped single-crystalline nanostructures are pure rutile-phase structure, with landscape dimension of 10-45 nm. EDS investigation confirms that the TiO2 nanosheets are only composed of Ti and O, and the atomic ration of Ti and O is close to 1:2. High photocatalytic activity might be expected for those TiO2 nanosheets due to their large surface area.

In this paper, finite element model (FEM) of a reinforced concrete structure cantilevered slab was established in non-linear finite element software ABAQUS. Influence of cantilever length and tensile reinforcement on the structural displacement and vibration frequency was calculated. The results show that the vibration frequency of the first order and maximum displacement will various with the diameter of the reinforced cantilever slab and the length of the cantilevered slab. This paper will offer the references to the analysis and design of the cantilever slab.

Electronic structure and chemical bonding in tetragonal KNbO3 have been studied by first-principles calculations. The band gap is indirect and a value of 1.64 eV was determined. Chemical bonding feature shows that a significant hybridization between Nb 4d and O 2p states. The bonding between K and NbO3 is mainly ionic nature while covalent nature was confirmed between Nb and O.

The deployable structure of the ring truss have advantage properties, which can be used as an effective supporting structure of deployable antenna. The deployable experiment of ring truss antenna showed that there was asynchronous phenomenon at the course of the deployment. Dynamics theory including constraint equations and considering friction factor are built firstly. Then simulation is studied systematically for the deployment process of ring truss deployable antenna. At last, the conclusions are obtained that the friction insulted in tensile forces of the cable drive decrease and the asynchronous phenomenon in the process of the deployment. It will give some help to the design and manufacture of the ring truss antenna.

In this paper, microstructure and mechanical properties of the chafer cuticle were investigated. The microstructures of the chafer cuticle were first observed with a SEM. It showed that the cuticle is a kind of chitin-fiber-reinforced biocomposite with protein matrix. There are some holes existing in the chafer cuticle and the fibers around hole are continuous. Based on the observed results of the SEM, the analyses of 3D models on the simple composite elements with fiber-round hole were conducted. The result showed the microstructures of composite laminates with fiber-round holes can decrease the stress concentration and well transfer the stress. So it can improve the strength and toughness of the composite laminates included holes. These conclusions may present a bio-inspired approach for design and development of advanced man-made fiber-reinforced composites.

The SEM observation on a conch’s shell shows that the shell is a kind of laminated bioceramic composite composed of aragonite layers and organic matrix. Each aragonite layer is parallel with the surface of the shell and consists of many thin aragonite sheets. These aragonite sheets are perpendicular to the layer where they are located. The observation also shows that the orientations of the sheets in different layers are different and these aragonite sheets compose various layups. A kind of lambdoidal layup is found. The maximum pullout force of the lambdoidal layup is analyzed based on its representative model. The result shows that the lambdoidal layup can markedly increase the pullout force of the layup and improve the fracture toughness of the shell.

Most structural materials existing in nature take the form of composite. After centuries’ evolution, these materials gain highly optimized microstructures and performances. In this work, a kind of natural biomaterial, shinbone, is observed with a scanning electron microscope (SEM). The observation result shows that the bone is a bioceramic composite consisting of hydroxyapatite layers and collagen matrix. The observation also shows that the hydroxyapatite layers are composed of hydroxyapatite sheets. The hydroxyapatite sheets are of thin and long shape and parallel distribution along the orientation of the maximum main stress of the bone. The shape and distribution of the hydroxyapatite sheets may endow the bone with favorable fracture toughness, which is analyzed and illuminated based a representational model of the hydroxyapatite sheets and the idea of maximum pullout force.

The microstructure of a Fragum unedo shell is observed with a scanning electronic microscope (SEM). It shows that the shell is a kind of bio-ceramic composite consisting of aragonite and collagen protein layers. The observation also shows that the aragonite layers consist of thin and long aragonite sheets. A kind of particular herringbone structure of the aragonite sheets is found. In the structure, the aragonite sheets in an arbitrary aragonite layer make a crossed angle against that in its neighboring aragonite layers. Based on the SEM observation the comparative experiments in the maximum pull-out forces of both the herringbone and conventional 0°-structures are conducted. It shows that the maximum pull-out force of the herringbone structure is markedly larger than that of the 0°-structure, and the larger the crossed angle is, the more the maximum pull-out force of the herringbone structure will increase compared with that of the 0°-structure.

Bone is a kind of biomaterial in nature. It behaves favorable strength, stiffness and fracture toughness which are closely related to its fine microstructure. SEM observation on a shankbone shows that the bone is a kind of natural bioceramic composite consisted of hydroxyapatite layers and collagen matrix. The observation also shows that the hydroxyapatite layers consist of many hydroxyapatite sheets and are arranged in a parallel distribution. The fracture toughness of the bone is analyzed based on the representative model of the microstructure of the bone and the idea of maximum pullout force. The analytical result shows that the long and thin shape as well as the parallel distribution of the hydroxyapatite sheets improves the maximum pullout force of the sheets and the fracture toughness of the bone.

Two novel epoxide hydrolases were discovered in mung bean (Phaseolus radiatus L.) for the first time, either of which can catalyze enantioconvergent hydrolysis of styrene epoxides. Their regioselectivity coefficients are more than 90% for the p-nitrostyrene oxide. Furthermore, the crude mung bean powder was also shown to be a cheap and practical biocatalyst, allowing a one-step asymmetric synthesis of chiral (R)-diols from racemic epoxides, in up to >99% ee and 68.7% overall yield (after recrystallization).

The reaction is best catalyzed by the (diphenylphosphino)(cyclohexyl)‐phenylthiourea and is applied to the various acrylates (II), (IV), acrolein (VIIIa) and methyl vinyl ketone (VIIIb).

Novel squaramides (I) containing a tertiary phosphine are developed and tested in the title reaction of ω‐formyl‐enone (II).

The phosphinothiourea shown in the scheme efficiently promotes asymmetric intramolecular Morita—Baylis—Hillman reaction of aldehydes of type (I).

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.