The first catalytic formal 5+4 cycloaddition to prepare nine‐membered heterocycles is presented. Under palladium catalysis, the reaction of N‐tosyl azadienes and substituted vinylethylene carbonates ...(VECs) proceeds smoothly to produce benzofuran‐fused heterocycles in uniformly high efficiency. Highly diastereoselective functionalization of the nine‐membered heterocycles through peripheral attack is also demonstrated.
On cloud nine: The first catalytic formal 5+4 cycloaddition is presented for the preparation of nine‐membered heterocycles. Under palladium catalysis, the reaction of N‐tosyl azadienes and substituted vinylethylene carbonates (VECs) proceeds smoothly to produce the benzofuran‐fused heterocycles with uniformly high efficiency. Highly diastereoselective functionalization of the nine‐membered heterocycles through peripheral attack is also demonstrated.
Seismic response of five-story frame structure supported by lead-rubber bearings isolation system is investigated subjected to near-fault ground motions. The main structure is modeled as a simple ...linear multi-degrees-of-freedom vibration system with lumped masses, excited by near-fault ground motions in the horizontal direction. The variation curves of peak top floor acceleration and peak bearing displacement of isolated building are plotted under different yield shear coefficient. The objective function selected for optimality is to maximize the seismic energy dissipated by the lead-rubber bearings. The main constraint conditions selected for optimality are the minimization of both peak bearing displacement and peak top floor acceleration. Optimum parameters of lead-rubber bearing isolation system are investigated and found that optimum yield shear coefficient of lead-rubber bearings is found to be in the range of 0.10–0.14 under near-fault ground motions. Optimum yield shear coefficient decreases with the increase of second isolation period. Optimum yield shear coefficient of lead-rubber bearings with higher yield displacement is larger than that of lead-rubber bearings with low yield displacement. Optimum ratio of pre-yield stiffness to post-yield stiffness of lead-rubber bearings is found to be in the range of 16–35. Optimum stiffness ratio increases proportionally with the decrease of yield displacement. Optimum stiffness ratio increases slightly with the increase of yield shear coefficient. Excluding the effect of pre-yield stiffness, the optimum second isolation period is recommended to be in the range of 4–6 s.
Highly efficient and diastereodivergent aza‐Diels–Alder reactions have been developed to access either diastereomeric series of benzofuran‐fused δ‐lactams and dihydropyridines in nearly perfect ...stereoselectivity (d.r. >20:1, >99 % ee for all examples). The complementarity of N‐heterocyclic carbene and chiral amine as the catalyst was demonstrated for the first time, together with an excellent level of catalytic efficiency (1 mol % loading).
The complementarity of a N‐heterocyclic carbene or chiral amine as the catalyst for aza‐Diels–Alder reactions was demonstrated. The highly efficient and diastereodivergent synthesis of benzofuran‐fused δ‐lactams and dihydropyridines was achieved in nearly perfect stereoselectivity (d.r. >20:1, >99 % ee for all examples).
Reported herein is the divergent syntheses of 5,5 and 6,5 spiro‐heterocycles under Lewis‐acid‐assisted palladium catalysis. In particular, an unprecedented switch from alkoxide‐π‐allyl to dienolate ...reactivity was achieved by the use of palladium‐titanium relay catalysis, and represents umpolung reactivity of vinylethylene carbonates. This method uses a simple procedure and commercially available catalysts, and delivers both classes of spiro‐heterocycles, bearing three contiguous stereocenters, in high yield and uniformly excellent diastereoselectivity.
Make the switch: Reported herein is the divergent syntheses of 5,5 and 6,5 spiro‐heterocycles under Lewis‐acid‐assisted palladium catalysis. A switch from alkoxide‐π‐allyl to dienolate reactivity was achieved using palladium‐titanium relay catalysis, and it represents umpolung reactivity of vinylethylene carbonates. This method uses a simple procedure and commercially available catalysts, and delivers both classes of spiro‐heterocycles bearing three contiguous stereocenters.
Core–shell composites, Fe3O4@C, with 500 nm Fe3O4 microspheres as cores have been successfully prepared through in situ polymerization of phenolic resin on the Fe3O4 surface and subsequent ...high-temperature carbonization. The thickness of carbon shell, from 20 to 70 nm, can be well controlled by modulating the weight ratio of resorcinol and Fe3O4 microspheres. Carbothermic reduction has not been triggered at present conditions, thus the crystalline phase and magnetic property of Fe3O4 micropsheres can be well preserved during the carbonization process. Although carbon shells display amorphous nature, Raman spectra reveal that the presence of Fe3O4 micropsheres can promote their graphitization degree to a certain extent. Coating Fe3O4 microspheres with carbon shells will not only increase the complex permittivity but also improve characteristic impedance, leading to multiple relaxation processes in these composites, thus the microwave absorption properties of these composites are greatly enhanced. Very interestingly, a critical thickness of carbon shells leads to an unusual dielectric behavior of the core–shell structure, which endows these composites with strong reflection loss, especially in the high frequency range. By considering good chemical homogeneity and microwave absorption, we believe the as-fabricated Fe3O4@C composites can be promising candidates as highly effective microwave absorbers.
A rhodium‐catalyzed intramolecular acetyl‐group transfer has been achieved through a “cut and sew” process. The challenge arises from the existence of different competitive pathways. Preliminary ...success has been achieved with unstrained enones that contain a biaryl linker. The use of an electron‐rich N‐heterocycilc carbene (NHC) ligand is effective to inhibit undesired β‐hydrogen elimination. Various 9,10‐dihydrophenanthrene derivatives can be prepared with excellent functional‐group compatibility. The 13C‐labelling study suggests that the reaction begins with cleavage of the unstrained C−C bond, followed by migratory insertion and reductive elimination.
Cross‐stitch: A rhodium‐catalyzed intramolecular acetyl‐group transfer has been achieved by a cut and sew process. By using unstrained enones that contain a biaryl linker, C−C activation occurs with the assistance of a temporary directing group. Various 9,10‐dihydrophenanthrene derivatives can be prepared with excellent functional‐group compatibility.
Rational design on the microstructure of electromagnetic composites offers immense potential for overcoming the challenges related to the microwave absorption performance. In this study, uniform ...core-shell Co@C microspheres are innovatively fabricated through an in situ transformation from Co3O4@phenolic resin precursor. Carbon shells restrain the agglomeration of Co particles during high-temperature treatment, which accounts for the survival of uniform core-shell microstructure. Electromagnetic analysis reveals that Co@C microspheres show quite different electromagnetic functions as compared with pure Co derived from Co3O4 microspheres. On one hand, carbon shells can effectively regulate the complex permittivity of Co@C microspheres by reducing conductivity loss and introducing polarization relaxations; on the other hand, carbon shells suppress the skin effect from cross-linked Co networks and make the isolated Co cores produce stronger magnetic loss. The microwave absorption properties are evaluated in the frequency range of 2.0–18.0 GHz, and as expected, core-shell Co@C microspheres exhibits excellent reflection loss characteristics, where strong reflection loss (−68.7 dB at 10.6 GHz), ultra-wide response bandwidth (2.7–18.0 GHz over −10 dB), and thin matched thickness (1.65 mm) can be achieved. A delta-function method and attenuation constant validate that the matched characteristic impedance and improved loss ability in Co@C microspheres account for the significant enhancement.
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The NOTCH2 gene plays a role in the development of many tumors. Deltex E3 ubiquitin ligase 3 (DTX3) was identified as a novel E3 ligase for NOTCH2 and as a potential therapeutic target for esophageal ...cancer. However, whether DTX3 could regulate NOTCH2 to suppress the progression of esophageal carcinoma remains unknown. In our study, NOTCH2 had higher expression in human esophageal carcinoma cell lines compared to normal human esophageal epithelial cell line, and ablation of NOTCH2 suppressed the proliferation and migration of esophageal carcinoma cells. A novel E3 ligase for NOTCH2 was identified by yeast two‐hybrid (Y2H) screening, and DTX3 promoted the ubiquitination and degradation of NOTCH2. Further study showed that DTX3 overexpression suppressed the proliferation and tumorigenicity of human oesophageal carcinoma cells. The analysis of tissue samples from patients revealed that the expression of NOTCH2 was high while the expression of DTX3 was low in esophageal cancer. Furthermore, the expression of DTX3 and NOTCH2 showed a significant negative correlation in human oesophageal cancer samples. Our study suggested that the DTX3‐NOTCH2 axis plays an important role in the progression of esophageal cancer, and DTX3 acts as an anti–oncogene in esophageal carcinoma, potentially offering a therapeutic target for esophageal cancer.
The DTX3‐NOTCH2 axis plays an important role in the progression of esophageal cancer, and DTX3 acts as an anti–oncogene in esophageal carcinoma, potentially offering a therapeutic target for esophageal cancer.
The first enantioselective formal 5+4 cycloaddition is realized under palladium catalysis to deliver benzofuran-fused nine-membered rings. These medium-sized heterocycles and derivatives undergo ...unique rearrangements induced by transannular bond formation, resulting in the production of two classes of densely substituted polycyclic heterocycles in excellent efficiency and stereoselectivity.
The out-of-time-ordered (OTO) correlation is a key quantity for quantifying quantum chaoticity and has been recently used in the investigation of quantum holography. Here we use it to study and ...characterize many-body localization (MBL). We find that a long-time logarithmic variation of the OTO correlation occurs in the MBL phase but is absent in the Anderson localized and ergodic phases. We extract a localization length in the MBL phase, which depends logarithmically on interaction and diverges at a critical interaction. Furthermore, the infinite-time “thermal” fluctuation of the OTO correlation is zero (finite) in the ergodic (MBL) phase and thus can be considered as an order parameter for the ergodic-MBL transition, through which the transition can be identified and characterized. Specifically, the critical point and the related critical exponents can be calculated.
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