Catalytic Enantioselective Propargylation of Pyrazolones by Amide-Based Phase-Transfer Catalysts.

In this paper, we developed a highly enantioselective alkylation of 4-substituted pyrazolones catalyzed by phase-transfer catalysis. Cheap halohydrocarbons were employed as electrophilic alkylationg agents, and propargyl, allyl, and benzyl products with all-carbon quaternary stereocenters were afforded with excellent enantioselectivities and good yields. We found that the unique structures of the catalyst (hydrogen bond donors of the C-9 hydroxyl group and amide group, the triphenyl at the NH-position) were important for good enantioselectivity. Furthermore, chiral propargyl products could be easily connected to azide molecules by click cycloaddition, which offers unique opportunities to obtain structurally diverse chiral pyrazolones.

Fluorescence-enhanced supra-amphiphiles based on pillar[5]arene: construction, controllable self-assembly and application in cell imaging.

Fluorescence-enhanced supra-amphiphiles based on (WP5)2⊃ENDTn were constructed successfully. When n = 9, they can self-assemble into uniform micelles with an average diameter of about 90 nm and be further applied in cell imaging.

Visible-Light-Promoted Aerobic α-Thiocyanation of Carbonyl Compounds with Ammonium Thiocyanate.

In the present study, we successfully developed an efficient thiocyanation of carbonyl compounds by using low-toxicity and inexpensive ammonium thiocyanate as the thiocyanate source under visible light in air (O2) at room temperature. This unified strategy is very facile for thiocyanation of various carbonyl compound derivatives (ß-keto esters, ß-keto amides, pyrazo-5-ones, isoxazol-5-ones, etc.). More importantly, the reaction proceeded smoothly without the addition of a photocatalyst and strong oxidant, ultimately minimizing the production of chemical waste. Furthermore, this green and sustainable synthetic chemistry can be used in the late-stage functionalization (LSF) of biorelevant compounds, which offers unique opportunities to achieve smooth and clean thiocyanation of drugs under mild reaction conditions.

Construction of an Angular Tricyclic Benzofuran Skeleton Using the C-H Activation Strategy.

A protocol for the construction of an angular tricyclic benzofuran skeleton based on the C-H activation strategy has been established. Different phthalide lactones on this skeleton can be easily assembled with various side chains by using C-H activation with aldehydes and subsequent reduction. This skeleton provides a versatile and crucial motif for the total synthesis of naturally occurring angular tricyclic benzofurans and their derivatives. Based on this protocol, the improved total syntheses of daldinin A and annullatin D were achieved in yields of 17.3 and 7.6%, respectively.

Photocatalyst-free visible-light-induced highly selective acylation of purine nucleosides at the C6 position.

A protocol for visible-light-induced C-H acylation selectively at the C6 position of purine nucleosides with aldehydes under photocatalyst-free conditions was established herein. This protocol allows the green, mild, and efficient functionalization of various purine nucleosides with a broad range of alkyl and aryl aldehydes.

Deaminative Cyclization of Tertiary Amines for the Synthesis of 2-Arylquinoline Derivatives with a Nonsubstituted Vinylene Fragment.

With triethylamine as a vinylene source, a convenient protocol for the regioselective synthesis of ß,γ-nonsubstituted 2-arylquinolines from aldehydes and arylamines has been accomplished. The deaminative cyclization is also extended to long-chain tertiary alkylamines, enabling diverse alkyl groups to be concurrently installed into the pyridine rings. This process demonstrates a new conversion pathway for the simultaneous dual C(sp3)-H bond functionalization of tertiary amines, wherein the transient acyclic enamines generated in situ undergo the Povarov reaction.

Open-Air Dual-Diamination of Aromatic Aldehydes: Direct Synthesis of Azolo-Fused 1,3,5-Triazines Facilitated by Ammonium Iodide.

A new and practical protocol for the synthesis of medicinally privileged azolo[1,3,5]triazines by simply heating under air has been presented. The in situ generated N-azolo amidines from commercially available aromatic aldehydes and 3-aminoazoles with ammonium iodide undergo the second diamination to accomplish the [3 + 1 + 1 + 1] heteroannulation reaction. This convenient process is appreciated by high efficiency, broad substrate scope, gram-scale synthesis, and operational simplicity under reagent-free conditions.

para-Selective hydroxylation of alkyl aryl ethers.

para-Selective hydroxylation of alkyl aryl ethers is established, which proceeds with a ruthenium(II) catalyst, hypervalent iodine(III) and trifluoroacetic anhydride via a radical mechanism. This protocol tolerates a wide scope of substrates and provides a facile and efficient method for preparing clinical drugs monobenzone and pramocaine on a gram scale.

Total Synthesis, Discovery and Biological Evaluation of Daldinin A Derivatives for Improving Hyperglycemia-Induced Endothelial Cell Death.

Daldinins are a novel type of naturally occurring tricyclic heterocycles isolated from Daldinia concentrica. In this study, four daldinin A derivatives with different alkyl side chains were synthesized using the same synthetic protocol. Bioactivity tests first indicated that the daldinin A derivatives showed significant protection for endothelial cells against damage caused by high glucose. The derivative compound with three carbon atoms on the alkyl side exhibited the best effect.

Asymmetric α-electrophilic difluoromethylation of ß-keto esters by phase transfer catalysis.

An efficient and enantioselective α-electrophilic difluoromethylation of ß-keto esters has been achieved by phase-transfer catalysis. This procedure is applicable to different kinds of ß-keto esters with a series of cinchona-derived C-2' aryl-substituted phase-transfer catalysts. The reaction gives the corresponding products in good enantioselectivities (up to 83% ee) and yields (up to 92%) with high C/O regioselectivities (up to 98 : 2). Moreover, the C/O selectivity of ß-keto esters could be easily reversed and controlled. This asymmetric difluoromethylation provided a novel and efficient way for introducing chiral C-CF2H groups.

Cytotoxicity of targeted PLGA nanoparticles: a systematic review.

Recent advances in nanotechnology have contributed tremendously to the development and revolutionizing of drug delivery systems in the field of nanomedicine. In particular, targeting nanoparticles based on biodegradable poly(lactic-co-glycolic acid) (PLGA) polymers have gained much interest. However, PLGA nanoparticles remain of concern for their effectiveness against cancer cells and their toxicity to normal cells. The aim of this systematic review is to identify a promising targeting PLGA nanoformulation based on the comparison study of their cytotoxicity potency in different cell lines. A literature search was conducted through the databases of Google Scholar, PubMed, ScienceDirect, Scopus and SpringerLink. The sources studied were published between 2009 and 2019, and a variety of keywords were utilized. In total, 81 manuscripts that met the inclusion and exclusion criteria were selected for analysis based on their cytotoxicity, size, zeta potential, year of publication, type of ligand, active compounds and cell line used. The half maximal inhibitory concentration (IC50) for cytotoxicity was the main measurement in this data extraction, and the SI units were standardized to µg mL-1 for a better view of comparison. This systematic review also identified that cytotoxicity potency was inversely proportional to nanoparticle size. The PLGA nanoparticles predominantly exhibited a size of less than 300 nm and absolute zeta potential ∼20 mV. In conclusion, more comprehensive and critical appraisals of pharmacokinetic, pharmacokinetic, toxicokinetic, in vivo and in vitro tests are required for the investigation of the full value of targeting PLGA nanoparticles for cancer treatment.

I2-Catalyzed Aerobic α,ß-Dehydrogenation and Deamination of Tertiary Alkylamines: Highly Selective Synthesis of Polysubstituted Pyrimidines via Hidden Acyclic Enamines.

A novel and efficient entrance to the pyrimidine skeleton has been presented via the α,ß-dehydrogenation and deamination of tertiary alkylamines. This I2-catalyzed dehydrogenative multicomponent procedure utilizes simple aldehydes to trap the hidden enamine intermediates and suspend generation of azadienes from amidines, enabling the difunctionalization of a vicinal C(sp3)-H bond. These studies provide valuable possibilities for the introduction of aliphatic substituents and show how to switch to a new reactive modality.

Contact and injection engineering for low SS reconfigurable FETs and high gain complementary inverters.

The newly emerged two-dimensional (2D) semiconducting materials, owning to the atomic thick nature and excellent optical and electrical properties, are considered as potential candidates to solve the bottlenecks of traditional semiconductors. However, the realization of high performance 2D semiconductor-based field-effect transistors (FETs) has been a longstanding challenge in 2D electronics, which is mainly ascribing to the presence of significant Schottky barrier (SB) at metal-semiconductor interfaces. Here, an additional contact gate is induced in 2D ambipolar FET to realize near ideal reconfigurable FET (RFET) devices without restrictions of SB. Benefitting from the consistently high doping of contact region, the effective SB height can be maintained at ultra-small value during all operation conditions, resulting in the near ideal subthreshold swing (SS) values (132 mV/decade for MoTe2 RFET and 67 mV/decade for WSe2 RFET) and the relatively high mobility (28.6 cm2/(V s) for MoTe2 RFET and 89.8 cm2/(V s) for WSe2 RFET). Moreover, the flexible control on the doping polarity of contact region enables the remodeling and switching of the achieved unipolar FETs between p-type mode and n-type mode. Based on such reconfigurable behaviors, high gain complementary MoTe2 inverters are further realized. The findings in this work push forward the development of high-performance 2D semiconductor integrated devices and circuits.

Microwave-Assisted Synthesis of Benzofuran-3(2H)-ones.

A new method for synthesis of benzofuran-3(2H)-one under microwave condition was investigated. The reaction conditon was screened and the eligible scope of benzoate substrates was also examined. It showed that this method could provide a short and facile way to obtain these important dihydrobenzofuranones in yield 43% to 58%.

Dynamic Kinetic Resolution for Construction of Three Transannular Stereocenters of Dihydrobenzofuranols.

A handy and effective method was established to obtain the cis-2,3-dihydrobenzofuranols having three stereocenters, involving asymmetric transfer hydrogenation of benzofuranones via dynamic kinetic resolution. The general applicability of this method was examined with different benzofuran-3-(2 H)-ones, and stereoselectivities of 85-99% ee and up to 98/2 dr were obtained.

PtSe2/graphene hetero-multilayer: gate-tunable Schottky barrier height and contact type.

Graphene-based two-dimensional hybrid materials are attracting significant attention because they can preserve novel characteristics of Dirac cone. Here, based on first-principles methods, we focus on the electronic characteristics of PtSe2/graphene hetero-multilayer. The negative binding energies indicate that the hybrid materials can be fabricated easily in practice. Also, the n-type Schottky contact is formed and its barrier height is robust to the number of graphene layer. Moreover, the gate-voltage can effectively induce the Schottky barrier transformation from n-type to p-type and contact type transformation from Schottky to Ohmic in the PtSe2/graphene hetero-multilayer. Thus, the work demonstrates that the graphene stacking configuration and gate-voltage will tune the electronic characteristics of PtSe2/graphene-based nanodevices.

Experimental and Computational Development of a Conformationally Flexible Template for the meta-C-H Functionalization of Benzoic Acids.

A conformationally flexible template for the meta-C-H olefination of benzoic acids was designed through both experimental and computational efforts. The newly designed template favors a silver-palladium heterodimer low barrier transition state, and demonstrates that it is feasible to lengthen templates so as to achieve meta-selectivity when the distance between the functional handle of the native substrate and target C-H bond decreases. Analysis of the ortho-, meta-, and para-C-H cleavage transition states determined that the new template conformation optimizes the interaction between the nitrile and palladium-silver dimer in the meta-transition state, enabling palladium to cleave meta-C-H bonds with moderate-to-good yields and generally high regioselectivity. Regioselectivity is governed exclusively by the template, and kinetic experiments reveal that there is a 4-fold increase in rate in the presence of monoprotected amino acid ligands. Using a Boltzmann distribution of all accessible C-H activation transition states, it is possible to computationally predict meta-selectivity in a number of investigated templates with reasonable accuracy. Structural and distortion energies reported may be used for the further development of templates for meta-C-H activation of hitherto unexplored arene substrates.

Tuning anisotropic electronic transport properties of phosphorene via substitutional doping.

Using first-principles calculations, we studied the anisotropic electronic transport properties of pristine and X-doped phosphorene (X = B, Al, Ga, C, Si, Ge, N, As, O, S, and Se atoms). The results show that doping different elements can induce obviously different electronic transport characteristics. Moreover, isovalent doping maintains semiconducting characteristics and anisotropic transport properties, while group IV and VI atoms doping can induce metal properties. Meanwhile, Al and Ga substituting P decrease the anisotropic behaviors of transport, and other atom doping still preserves anisotropic characteristics. Interestingly, obvious negative differential resistance behaviors can be observed in C, Si, Ge, O, S, and Se-doped phosphorene.

Ligand-enabled meta-C-H activation using a transient mediator.

Achieving site selectivity in C-H functionalization reactions is a significant challenge, especially when the target C-H bond is distant from existing functional groups. Coordination of a functional group to a metal is often a key driving force and control element in many important reactions including asymmetric hydrogenation, epoxidation and lithiation. Exploitation of this effect has led to the development of a broad range of directed C-H activation reactions. However, these C-H activation methods are limited to proximal C-H bonds, which are spatially and geometrically accessible from the directing functional group. The development of meta-selective C-H functionalizations remains a significant challenge. We recently developed a U-shaped template that can be used to overcome this constraint and have shown that it can be used to selectively activate remote meta-C-H bonds. Although this approach has proved to be applicable to various substrates and catalytic transformations, the need for a covalently attached, complex template is a substantial drawback for synthetic applications. Here we report an alternative approach employing norbornene as a transient mediator to achieve meta-selective C-H activation with a simple and common ortho-directing group. The use of a newly developed pyridine-based ligand is crucial for relaying the palladium catalyst to the meta position by norbornene after initial ortho-C-H activation. This catalytic reaction demonstrates the feasibility of switching ortho-selectivity to meta-selectivity in C-H activation of the same substrate by catalyst control.