Heteroatom-Controlled Three-Component [4 + 3] or [3 + 2] Annulation of Isatin-Derived Azomethine Ylide with Azadiene: Selective Synthesis of Spirooxindole-diazepines and Density Functional Theory Studies.

A novel three-component [4 + 3] annulation reaction of isatin-derived azomethine ylides with azadienes was developed for the first time to efficiently synthesize spirooxindole-diazepines incorporating a benzothiophene moiety under catalyst-free conditions. Effects of the heteroatom of azadiene on the chemoselectivity was investigated. With the use of the azadiene bearing a benzofuran moiety as a substrate, the dominant reaction pathway was changed to an α-[3 + 2] annulation. When azadiene bearing an indenone moiety was used, a distinct γ-[3 + 2] annulation was observed. Density functional theory calculations revealed that a delicate balance between kinetic accessibility and the thermodynamic driving force controlled the competition of different annulation reactions.

Acceptor-donor-acceptor type organic photothermal agents with enhanced NIR absorption and photothermal conversion effect for cancer photothermal therapy.

Numerous photothermal agents (PTAs) require high-intensity and long-duration laser excitation for photothermal therapy (PTT), resulting in light damage to healthy skin and tissue as well as limiting their biomedical applications. Integrating desirable near-infrared (NIR) absorption and high photothermal conversion efficiency (PCE) into a single small-molecule PTA is an important prerequisite for realizing efficient PTT, but is a serious challenge. Herein, through molecular engineering strategy, an acceptor-donor-acceptor (A-D-A) type PTA (ADA3) was readily developed for 808 nm laser-driving photothermal imaging and PTT of tumor. Theoretical calculations and experiment results show molecular engineering strategy is significant in regulating the structure and energy gap of PTAs, so as to effectively induce a narrow band gap for NIR absorption and further optimize photothermal properties. ADA3 possesses molar extinction coefficient of 3.1 × 104 M-1 cm-1 at 808 nm, followed being assembled into nanoparticles, ADA3-NPs show high PCE of 80.3%. In vivo experiments indicate that ADA3-NPs have excellent antitumor capability under one-time, low-intensity and short-duration (808 nm, 330 mW/cm2, 3 min) laser irradiation. Therefore, this work definitely exemplifies the enormous potential of molecular engineering strategy and provides an effective method for developing small-molecule PTAs.

Electrochemical Ring-Opening of Cyclopropylamides with Alcohols toward the Synthesis of 1,3-Oxazines.

An electrochemical method is presented to construct 1,3-oxazines by the oxidative ring-opening of cyclopropylamides with alcohols. This method avoids the use of external oxidants and thus shows good functional group tolerance. The substrate scope covers primary, secondary, and tertiary alcohols as well as (hetero)aryl amide-substituted cyclopropanes.

Mechanisms and heterogeneity in the construction of network infrastructure to help rural households bridge the "digital divide".

Addressing the digital divide that plagues rural areas has become an important issue in narrowing the urban-rural gap and achieving common prosperity. This article examines the impact of network infrastructure on rural households' ability to cross the digital divide by using the "broadband rural" strategy as a proxy variable for network infrastructure and combining data from the China Family Panel Studies (CFPS) with a score propensity matched difference-in-differences model (PSM-DID). The results show that network infrastructure can help farmers cross the access and use divide, but does not contribute significantly to crossing the ability divide in the current period. A triple difference model (DDD) was introduced to test the effect of network technology training on the contribution of network infrastructure to the ability gap, and the ability gap needs to be based on the use gap, so there is a delay in the response of the ability gap to policy. Further analysis reveals that network infrastructure mainly facilitates non-farm occupational groups to cross the capability divide, and facilitates middle-aged and young people to cross the digital divide, and does not have significant effects on groups involved in agricultural work and older people. In view of this, the network infrastructure should be continuously promoted, public service training on digital skills should be organized, electronic products and information services should be created exclusively for the elderly group and the group involved in agricultural production, and the ability of farmers to apply the network to their production life should be strengthened.

Construction of Polyaromatic Hydrocarbons Containing Sulfur and Nitrogen via Controllable Domino Reactions and DFT Studies.

Polyaromatic hydrocarbons (PHAs) containing heteroatoms have attracted considerable attention due to their potential utility in electronic devices. This work reported a novel domino reaction between an aryne precursor and azadiene bearing a benzothiophene moiety to produce a series of PHAs containing sulfur and nitrogen atoms. Further transformation of the product enabled concise synthesis of a new AIEgen, whose photophysical properties were characterized. Density functional calculations on the reaction mechanism revealed that the in situ generated aryne could trigger either a [4 + 2] or [3 + 2] process with azadiene, in which the regioselectivity was mainly a result of the heteroatom effect and may be understood by means of Houk's distortion-interaction model.

Self-Assembly 2D Ti3C2/g-C3N4 MXene Heterojunction for Highly Efficient Photocatalytic Degradation of Tetracycline in Visible Wavelength Range.

An ultrathin 2D Ti3C2/g-C3N4 MXene (2D-TC/CN) heterojunction was synthesized, using a facile self-assembly method; the perfect microscopic-morphology and the lattice structure presented in the sample with a 2 wt% content of Ti3C2 were observed by the field-emission scanning electron microscopy (SEM) and transmission electron microscope (TEM). The optimized sample (2-TC/CN) exhibited excellent performance in degrading the tetracycline (TC), and the degradation rate reached 93.93% in the conditions of 20 mg/L, 50 mL of tetracycline within 60 min. Except for the increased specific-surface area, investigated by UV-vis diffuse reflectance spectra (UV-vis DRS) and X-ray photoelectron microscopy (XPS) valence spectra, the significantly enhanced photocatalytic activity of the 2-TC/CN could also be ascribed to the formation of Ti-N bonds between Ti3C2 and g-C3N4 nanosheets, which reduced the width of the band gap through adjusting the position of the valence band, thus resulting in the broadened light-absorption. Furthermore, the facilitated electron transmission was also proved by time-resolved photoluminescence (TRPL) and electrochemical impedance spectroscopy (EIS), which is effective in improving the quantum efficiency of photo-generated electrons. In addition, the resulting radical-capture experiment suggested that superoxide radicals have the greatest influence on photodegradation performance, with the photodegradation rate of TC reducing from 93.16% to 32.08% after the capture of superoxide radicals, which can be attributed to the production of superoxide radicals only, by the 2-TC/CN composites with a high conduction-band value (-0.62 eV). These facilely designed 2D Ti3C2/g-C3N4 composites possess great application potential for the photodegradation of tetracycline and other antibiotics.

Switchable C2/C3 positional selectivity of thioisatins in a three-component domino reaction: combined computational and experimental studies.

The nucleophile-induced domino reaction is a featured reactivity mode of thioisatin, but the C2/C3 positional selectivity towards a nucleophile has not been understood in-depth. In this work, a domino reaction of thioisatin with bromoacetophenone and tryptamine hydrochloride to produce a benzothiophene-fused eight-membered N-heterocycle was described, showing that the Brønsted acid-base form of the amine partner was crucial for the selectivity, because using tryptamine instead of tryptamine hydrochloride gave a different product. Control experiments and density functional calculations revealed that the domino reaction using tryptamine or tryptamine hydrochloride was triggered by a condensation reaction at the C2 or C3 position of thioisatin, respectively. A delicate balance between local electrophilicity and polarization effect may be responsible for the observed selectivity.

Sustainable access to benzothiophene derivatives bearing a trifluoromethyl group via a three-component domino reaction in water.

A catalyst-free three-component domino reaction was developed for the synthesis of benzothiophene fused pyrrolidones bearing a CF3 group for the first time. The notable advantages of this strategy over the existing methods include the use of water as a solvent at room temperature, transition metal-free conditions, a broad substrate scope, and easy scale-up synthesis. More importantly, the benzothiophene derivatives have been found to show potent anticancer activities using the Cell Counting Kit-8 (CCK-8) assay.

Stereoselective [4 + 3] annulation of azadienes and ethyl 4-bromo-3-oxobutanoate: construction of benzindeno-fused azepine derivatives.

The benzindenoazepine ring system is an attractive scaffold for biologically active compounds. This work reported a NaH-promoted cycloaddition between azadienes and ethyl 4-bromo-3-oxobutanoate, which delivered a series of benzindenoazepines with good yields and stereoselectivities. Such benzindenoazepine derivatives were not easily obtained by using a traditional approach. The application of this cycloaddition strategy has been extended to azadienes bearing a benzofuran or benzothiophene moiety. The utility of this method was showcased by gram-scale experiments and synthetic transformations of the product.

Catalyst-controlled switchable [4 + 1], [4 + 3] and [3 + 2] domino reactions of azadienes and MBH carbonates: diverse synthesis of benzothiophene fused derivatives.

Catalyst-controlled switchable domino reactions between azadienes bearing a benzothiophene moiety and isatin-derived MBH carbonates were developed. The [4 + 1] annulation was triggered in the presence of DABCO, giving a variety of benzothiophene fused pyrrole derivatives, while the [4 + 3] annulation occurred when changing the catalyst to DMAP. Furthermore, the [3 + 2] annulation mode was observed with the use of catalytic Ph2PMe. Additionally, the synthetic utility of these domino reactions was demonstrated by gram-scale experiments and simple transformations of the products. To the best of our knowledge, catalyst-controlled synthesis of benzothiophene fused or spiro derivatives has rarely been reported.

Synthesis of 2-(Cyanomethyl)benzoic Esters via Carbon-Carbon Bond Cleavage of Indanones.

A novel synthesis of 2-(cyanomethyl)benzoic esters from indanone derivatives has been established. This reaction proceeds via a deprotonation of alcohols with a chemical base, followed by a nucleophilic addition to indanones and Beckmann fragmentation. In addition, this reaction could also work under electrochemical conditions, and no external chemical bases were needed. This mild method offers a novel strategy for the late-stage functionalization of various natural alcohols.

Divergent Construction of Benzothiophene-Fused N-Heterocycles via Stereotunable Three-Component Domino Reactions.

A stereotunable three-component domino strategy among thioisatin, 2-bromo-1-phenylethan-1-one, and cyclohexane-1,2-diamine under catalyst-free conditions was disclosed. A wide range of benzothiophene-fused polycycles and eight-membered N-heterocycles were synthesized by regulating the stereoconfiguration of cyclohexane-1,2-diamines. The detailed mechanism and the origin of the chemoselectivity were explored by density functional calculations. Analysis of the geometrical structures of key transition states revealed that the existence of favorable intramolecular attractions, and the steric effect governed the chemoselectivity observed.

Construction of Benzothiophene or Benzothiopheno[2,3-e]azepinedione Derivatives via Three-Component Domino or One-Pot Sequences.

An efficient three-component domino or one-pot strategy has been developed for the synthesis of medicinally important benzothiophene and benzothiopheno[2,3-e]azepinedione derivatives for the first time. Amine-promoted selective cleavage of C-S bond of thioisatin is the key step in this process. The reported methodology benefits from environmentally friendly solvent (H2O), wide substrate scope, good functional group tolerance, and high reaction yields.

Electrochemically Enabled Sulfonylation of Alkynes with Sodium Sulfinates.

An electrochemical sulfonylation of alkynes with sodium sulfinates was achieved for the first time at room temperature. Employing this electrolysis strategy, the reaction occurs efficiently under transition-metal-free, external oxidant-free, and base-free conditions and furnishes diverse alkynyl sulfones in satisfactory yield with broad functional group tolerance.

Recent Advances in the Cycloaddition Reactions of 2-Benzylidene-1-benzofuran-3-ones, and Their Sulfur, Nitrogen and Methylene Analogues.

Benzothiophene, benzofuran, indole, and indene derivatives are privileged heterocyclic motifs. These are present in a wide range of bioactive natural products and pharmaceutical drugs and are the subject of materials science research. However, the construction of benzothiophene, benzofuran, indole, and indene frameworks have been long-standing challenges to organic chemists. In this review, we classify the derivatives of four structures synthesized from 2-benzylidene-1-benzofuran-3-one and their analogues in terms of their ring size (from three- to ten-membered) and type (fused or spiro), as well as summarizing the developments of this field. Finally, we discuss the ring opening and 1,4-addition reactions.

Construction of [6-5-5-6-6] Pentacyclic Skeleton via a Phosphine-Catalyzed Domino Reaction and Mechanism Study.

A novel phosphine-promoted domino reaction between thioaurone or aurone derivatives and MBH carbonate is described. A wide range of [6-5-5-6-6] pentacyclic compounds was prepared efficiently. Interestingly, the stereoselectivity was affected by the sulfur or oxygen atom in the substrates. Moreover, the reaction mechanism was explored by density functional calculations, which identified the 1,4-hydrogen-shift step to be the selectivity-determining step.

Electrochemical Oxidative Oxydihalogenation of Alkynes for the Synthesis of α,α-Dihaloketones.

An electrochemical oxydihalogenation of alkynes has been developed for the first time. Using this sustainable protocol, a variety of α,α-dihaloketones can be prepared with readily available CHCl3, CH2Cl2, ClCH2CH2Cl, and CH2Br2 as the halogen source under electrochemical conditions at room temperature.

Construction of Eight-Membered Cyclic Diaryl Sulfides via Domino Reaction of Arynes with Thioaurone Analogues and DFT Study on the Reaction Mechanism.

Eight-membered cyclic and [5,5]-bicyclic sulfides were synthesized via a domino reaction between thioaurone analogues and arynes. Density functional theory calculations were performed to elucidate the reaction mechanism, which involves the elementary steps of the [3 + 2] cycloaddition, 1,2-hydrogen shift, and C(sp2)-S bond cleavage as well as the substituent effect.

Synthesis of polysubstituted cyclic 1,2-diketones enabled by iterative sulfoxide-mediated arylation.

A metal-free α-C-H functionalization of cyclic 1,2-diketones with aryl sulfoxides has been developed. This regioselective arylation involves nucleophilic substitution at the activated sulfoxide with a diosphenol, followed by [3,3]-sigmatropic rearrangement. This protocol can also be applied to the synthesis of polysubstituted cyclic 1,2-diketones with predictable structures by iterative arylations.

Synthesis of Benzothiophene-Fused Oxa[6.6.5]tricyclic Skeletons through a Cinchonidine- or NaOH-Promoted Quadruple Domino Sequence.

Two base-promoted quadruple domino reactions between thioaurones and allylic phosphonium salts have been developed to synthesize benzothiophene-fused oxa[6.6.5]tricyclic skeletons in moderate to good yields with excellent stereoselectivity and broad functional-group tolerance. This is a simple and useful protocol for the rapid construction of the umbrella-like oxa[6.6.5]tricyclic skeleton.