Nickel-Catalyzed Enantioselective Synthesis of 2,3,4-Trisubstituted 3-Pyrrolines.

The development of synthetic methods to produce highly functionalized chiral 3-pyrrolines is of indisputable importance because of their prevalence in natural and synthetic bioactive molecules. Unfortunately, previous general cycloaddition approaches using allenoates, could not synthesize 3,4-disubstituted 3-pyrrolines. Herein, an original approach to yield 2,3,4-trisubstituted 3-pyrrolines with chirality at the 2-position is presented. A NiII /Fc-i-PrPHOX catalytic system facilitated a redox-neutral highly stereoselective process that exhibited an enantioselectivity of up to 99 %. Enantioenriched 3-pyrrolines can be converted to other valuable classes of N-heterocycles.

Benzothiazole Synthesis: Mechanistic Investigation of an In Situ-Generated Photosensitizing Disulfide.

The use of a visible light absorbing intermediate as a photosensitizer makes a chemical process simple and sustainable, obviating the need for the use of chemical additives. Herein, the formation of a photosensitizing disulfide in benzothiazole synthesis from 2-aminothiophenol and aldehydes was proposed and confirmed through in-depth mechanistic studies. A series of photophysical and electrochemical investigations revealed that an in situ-generated disulfide photosensitizes molecular oxygen to generate the key oxidants, singlet oxygen and superoxide anion, for the dehydrogenation step.

Generation of N-Centered Radicals via a Photocatalytic Energy Transfer: Remote Double Functionalization of Arenes Facilitated by Singlet Oxygen.

An unprecedented approach to the generation of an N-centered radical via a photocatalytic energy-transfer process from readily available heterocyclic precursors is reported, which is distinctive of the previous electron transfer approaches. In combination with singlet oxygen, the in-situ-generated nitrogen radical from the oxadiazoline substrate in the presence of fac-Ir(ppy)3 undergoes a selective ipso addition to arenes to furnish remotely double-functionalized spiro-azalactam products. The mechanistic studies provide compelling evidence that the catalytic cycle selects the energy-transfer pathway. A concurrent activation of molecular oxygen to generate singlet oxygen by energy transfer is also rationalized. Furthermore, the occurrence of the electron transfer phenomenon is excluded on the basis of the negative driving forces for one-electron transfer between oxadiazoline and the excited state of fac-Ir(ppy)3 with a consideration of their redox potentials. The necessity of singlet oxygen as well as the photoactivated oxadiazoline substrate is clearly supported by a series of controlled experiments. Density functional studies have also been carried out to support these observations. The scope of substrates is explored by synthesizing diversely functionalized cyclohexadienone moieties in view of their utility in complex organic syntheses and as potential targets in pharmacology.

Dual Photoredox and Nickel Catalysis in Regioselective Diacylation: Exploring the Versatility of Nickel Oxidation States in Allene Activation.

We present a nickel-catalyzed regioselective radical diacylation of allenes with ketoacids to produce 1,4-dione products by dual photoredox and nickel catalysis. This integrated approach merges redox-active oxidative addition and reductive elimination steps with migratory insertion. The acyl radical generated in the photoredox cycle sequentially adds to Ni(I) and Ni(II) intermediates following a Ni(I)-Ni(II)-Ni(II)-Ni(III)-Ni(I) catalytic cycle. This methodology, supported by DFT calculations, demonstrates the potential of nickel catalysis in the creation of complex molecular architectures.

Photocatalytic para-Selective C-H Functionalization of Anilines with Diazomalonates.

Visible-light-induced para-selective C-H functionalization of anilines over N-H insertion was developed using diazomalonates with the help of an Ir(III) photocatalyst. The para-selective radical-radical cross coupling proceeded via C-centered radical intermediates generated from both anilines and diazomalonates. The photochemistry of anilines could be extended to other N-heterocycles, such as indole and carbazole. The reaction pathway for the selective C-C coupling was validated by electrochemical and photophysical experiments as well as computational studies.

Energy Transfer Photocatalytic Radical Rearrangement in N-Indolyl Carbonates.

A new type of sp3-like N-centered radical has been generated by selective energy transfer catalysis. Upon photoexcitation, homolytic N-O bond cleavage of N-indolyl carbonate in the presence of an Ir complex produced N- and O-centered radicals. The high spin density at the C3 position of indole led to radical recombination with the O-centered radical, affording valuable 3-oxyindole derivatives without decarboxylation. Transformations of the desired products into various molecules were also demonstrated.

Molecular-Level Lubrication Effect of 0D Nanodiamonds for Highly Bendable Graphene Liquid Crystalline Fibers.

Graphene fiber is emerging as a new class of carbon-based fiber with distinctive material properties particularly useful for electroconductive components for wearable devices. Presently, stretchable and bendable graphene fibers are principally employing soft dielectric additives, such as polymers, which can significantly deteriorate the genuine electrical properties of pristine graphene-based structures. We report molecular-level lubricating nanodiamonds as an effective physical property modifier to improve the mechanical flexibility of graphene fibers by relieving the tight interlayer stacking among graphene sheets. Nanoscale-sized NDs effectively increase the tensile strain and bending strain of graphene/nanodiamond composite fibers while maintaining the genuine electrical conductivity of pristine graphene-based fibers. The molecular-level lubricating mechanism is elucidated by friction force microscopy on the nanoscale as well as by shear stress measurement on the macroscopic scale. The resultant highly bendable graphene/nanodiamond composite fiber is successfully weaved into all graphene fiber-based textiles and wearable Joule heaters, proposing the potential for reliable wearable applications.

Complementary Reactivity in Selective Radical Processes: Electrochemistry of Oxadiazolines to Quinazolinones.

Electrochemistry has recently emerged as a sustainable approach for efficiently generating radical intermediates utilizing eco-friendly electric energy. An electrochemical process was developed to transform 1,2,4-oxadiazolines under mild conditions. The electrochemical N-O bond cleavage at a controlled oxidation potential led to the selective synthesis of quinazolinone derivatives that could not be obtained by photocatalytic radical processes, indicating complementary reactivities in radical processes. The electrochemical reaction pathways were fully revealed by density functional theory-based investigations.

Boosting Photoredox Catalysis Using a Two-Dimensional Electride as a Persistent Electron Donor.

Electrides, which have excess anionic electrons, are solid-state sources of solvated electrons that can be used as powerful reducing agents for organic syntheses. However, the abrupt decomposition of electrides in organic solvents makes controlling the transfer inefficient, thereby limiting the utilization of their superior electron-donating ability. Here, we demonstrate the efficient reductive transformation strategy which combines the stable two-dimensional [Gd2C]2+·2e- electride electron donor and cyclometalated Pt(II) complex photocatalysts. Strongly localized anionic electrons at the interlayer space in the [Gd2C]2+·2e- electride are released via moderate alcoholysis in 2,2,2-trifluoroethanol, enabling persistent electron donation. The Pt(II) complexes are adsorbed onto the surface of the [Gd2C]2+·2e- electride and rapidly capture the released electrons at a rate of 107 s-1 upon photoexcitation. The one-electron-reduced Pt complex is electrochemically stable enough to deliver the electron to substrates in the bulk, which completes the photoredox cycle. The key benefit of this system is the suppression of undesirable charge recombination because back electron transfer is prohibited due to the irreversible disruption of the electride after the electron transfer. These desirable properties collectively serve as the photoredox catalysis principle for the reductive generation of the benzyl radical from benzyl halide, which is the key intermediate for dehalogenated or homocoupled products.

Direct C(sp3)-N Radical Coupling: Photocatalytic C-H Functionalization by Unconventional Intermolecular Hydrogen Atom Transfer to Aryl Radical.

An unconventional approach for intermolecular direct C(sp3)-N radical coupling has been developed by photocatalytic C(sp3)-H activation of simple alkyl substrates using O-benzoyl oximes. The selective photocatalytic energy-transfer-driven homolysis followed by decarboxylation generates the persistent iminyl radical and aryl radical, which would undergo an unprecedented intermolecular hydrogen atom abstraction from the alkyl substrate to provide the key C(sp3) radical. Selective radical-radical C-N cross-coupling furnishes imines which are valuable amine building blocks.

Transforming Oxadiazolines through Nitrene Intermediates by Energy Transfer Catalysis: Access to Sulfoximines and Benzimidazoles.

Subtle differences in reaction conditions facilitated unprecedented photocatalytic reactions of oxadiazolines by energy transfer catalysis. A set of compounds, sulfoximines and benzimidazoles, were ingeniously prepared from oxadiazolines via nitrene intermediates by photocatalytic N-O/C-N bond cleavages. The synthesis of sulfoximines was realized through intermolecular N-S bond formation between nitrene intermediates and sulfoxides, whereas benzimidazoles were obtained via intramolecular aromatic substitution of the nitrene to the tethered aryl substituent.

Self-Planarization of High-Performance Graphene Liquid Crystalline Fibers by Hydration.

Graphene fibers (GFs) are promising elements for flexible conductors and energy storage devices, while translating the extraordinary properties of individual graphene sheets into the macroscopically assembled 1D structures. We report that a small amount of water addition to the graphene oxide (GO) N-methyl-2-pyrrolidone (NMP) dispersion has significant influences on the mesophase structures and physical properties of wet-spun GFs. Notably, 2 wt % of water successfully hydrates GO flakes in NMP dope to form a stable graphene oxide liquid crystal (GOLC) phase. Furthermore, 4 wt % of water addition causes spontaneous planarization of wet-spun GFs. Motivated from these interesting findings, we develop highly electroconductive and mechanically strong flat GFs by introducing highly crystalline electrochemically exfoliated graphene (EG) in the wet-spinning of NMP-based GOLC fibers. The resultant high-performance hybrid GFs can be sewn on cloth, taking advantage of the mechanical robustness and high flexibility.

Mussel Inspired Highly Aligned Ti3C2Tx MXene Film with Synergistic Enhancement of Mechanical Strength and Ambient Stability.

Two-dimensional (2D) MXene has shown enormous potential in scientific fields, including energy storage and electromagnetic interference (EMI) shielding. Unfortunately, MXene-based material structures generally suffer from mechanical fragility and vulnerability to oxidation. Herein, mussel-inspired dopamine successfully addresses those weaknesses by improving interflake interaction and ordering in MXene assembled films. Dopamine undergoes in situ polymerization and binding at MXene flake surfaces by spontaneous interfacial charge transfer, yielding an ultrathin adhesive layer. Resultant nanocomposites with highly aligned tight layer structures achieve approximately seven times enhanced tensile strength with a simultaneous increase of elongation. Ambient stability of MXene films is also greatly improved by the effective screening of oxygen and moisture. Interestingly, angstrom thick polydopamine further promotes the innate high electrical conductivity and excellent EMI shielding properties of MXene films. This synergistic concurrent enhancement of physical properties proposes MXene/polydopamine hybrids as a general platform for MXene based reliable applications.

Facile Synthesis of BiVO4 for Visible-Light-Induced C-C Bond Cleavage of Alkenes to Generate Carbonyls.

BiVO4 crystals synthesized by an ultrasonic-assisted method (Sono-BiVO4 ) showed improved efficiency as a heterogeneous photocatalyst under visible-light irradiation. Sono-BiVO4 was successfully used for the C-C bond cleavage of alkenes to generate carbonyl compounds. Styrene derivatives were converted into carbonyl compounds in the presence of Sono-BiVO4 under highly sustainable conditions requiring only natural sources, that is, molecular oxygen, visible light, and water at room temperature. Additionally, Sono-BiVO4 could be easily separated from the reaction mixture and reused.

Conformal 3D Nanopatterning by Block Copolymer Lithography with Vapor-Phase Deposited Neutral Adlayer.

Block copolymer (BCP) lithography is an effective nanopatterning methodology exploiting nanoscale self-assembled periodic patterns in BCP thin films. This approach has a critical limitation for nonplanar substrate geometry arising from the reflow and modification of BCP films upon the thermal or solvent annealing process, which is inevitable to induce the mobility of BCP chains for the self-assembly process. Herein, reflow-free, 3D BCP nanopatterning is demonstrated by introducing a conformally grown adlayer by the initiated chemical vapor deposition (iCVD) process. A highly cross-linked poly(divinylbenzene) layer was deposited directly onto the BCP thin film surface by iCVD, which effectively prevented the reflow of BCP thin film during an annealing process. BCP nanopatterns could be stabilized on various substrate geometry, including a nonplanar deformed polymer substrate, a pyramid shape substrate, and a graphene fiber surface. A fiber-type hydrogen evolution reaction (HER) catalyst is suggested by stabilizing lamellar Pt nanopatterns on severely rough graphene fiber surfaces.

Visible-Light-Promoted Synthesis of Fluoroalkylated Oximes.

A method has been developed for the synthesis of fluoroalkylated oximes, potential fluoroalkyl building-blocks for the synthesis of various organofluorine compounds, from easily available amino substrates and fluoroalkylated alkenes. tBuONO was utilized both as a diazotizing agent and as a NO radical source for the oxime synthesis in the process, and the use of a photocatalyst under visible-light irradiation increased the efficiency of the reaction. Various fluoroalkylated oximes were prepared by a tandem process of aryl radical addition to fluoroalkylated alkene and consecutive oxime generation process, albeit in moderate yields. This differentiated approach, transferring an aromatic system into an electron-deficient fluoroalkylated alkene, expands the scope of substrates where electron-poor aromatic systems could be utilized.

Lamellar stack formation and degradative behaviors of hydrolytically degraded poly(ε-caprolactone) and poly(glycolide-ε-caprolactone) blended fibers.

Electrospun fibrous mats have gained popularity in bioengineering over the past decade, but few papers detail their degradative mechanisms. To address this, blends of hydrophobic poly(ε-caprolactone) (PCL) and hydrophilic PGA-PCL-PGA triblock copolymer were electrospun into aligned fibrous mats to assess the copolymers' mechanical and degradative properties. Increased hydrophilic triblock content led to enhanced morphological uniformity of fiber, tightening of fiber diameters, increased storage and Young's modulus, and decreased elongation. The corresponding decrease in hydrophobic PCL content led to faster hydrolytic degradation rate, as reflected by enhanced decrease in mass, molecular weight, and modulus loss at 25, 37, and 45°C. The activation energy for hydrolytic degradation for 15:85 PCL: triblock copolymer was approximately half that of 85:15 PCL: triblock copolymer. Detailed examination of fiber morphology and crystallinity revealed initial surface erosion followed by the evolution of crystalline lamellar stacks and bulk degradation at 37°C. Because of the high surface to volume and short diffusion length scale of the small diameter fibers, surface and bulk degradation may both contribute to the hydrolytic degradative behavior of these electrospun fibrous mats. Electrospun mats' distinct architecture that embodies high specific surface to volume and interfiber porous ultrastructures that lead to their unique degradative behaviors hold much potential for significant impact in the field of tissue engineering and controlled drug delivery.

Detection of a large-scale structure of intracluster globular clusters in the Virgo cluster.

Globular clusters are usually found in galaxies, and they are excellent tracers of dark matter. Long ago it was suggested that intracluster globular clusters (IGCs) may exist that are bound to a galaxy cluster rather than to any single galaxy. Here we present a map showing the large-scale distribution of globular clusters over the entire Virgo cluster. It shows that IGCs are found out to 5 million light years from the Virgo center and that they are concentrated in several substructures that are much larger than galaxies. These objects might have been mostly stripped off from low-mass dwarf galaxies.