The Mizoroki-Heck reaction and its reductive analogue are staples of organic synthesis, but the ensuing products often lack a chemical handle for further transformation. Here we report an ...atom-economical cross-coupling of halopyridines and unactivated alkenes under photoredox catalysis to afford a series of alkene halopyridylation products. This protocol with mild and redox neutral conditions contributes broad substrate scope. As a complement to conventional Heck-type reaction, this radical process avoids the involvement of β-H elimination and thus useful pyridyl and halide groups could be simultaneously and regioselectively incorporated onto alkenes. The success depends on TFA-promoted domino photocatalytic oxidative quenching activation and radical-polar crossover pathway. Plausible mechanism is proposed based on mechanistic investigations. Moreover, the reserved C - X bonds of these products are beneficial for performing further synthetic elaborations.
In this work, we systematically investigate the photocatalytic mechanism of g-C3N4/BiOI (001) through hybrid functional calculations based on first-principles theory. The staggered band structure is ...observed in the g-C3N4/BiOI (001); meanwhile, a built-in electric field exists from the g-C3N4 monolayer to the BiOI surface at the interface. BiOI has lower band edges, which bend downward at the interface; whereas g-C3N4 has higher band edges, which bend upward. With Coulomb interaction and the built-in electric field, photo-generated electrons in the conduction bands (CB) of BiOI recombine with photo-generated holes in the valence bands (VB) of g-C3N4. Meanwhile, the stronger reduction capacity for photo-excited electrons in the g-C3N4's CB and the stronger oxidation capacity for photo-generated holes in the BiOI (001)'s VB are retained. Therefore, a direct Z-scheme heterostructure character is presented. As a result, the electrons and holes generated by the photons can be separated and migrate highly effectively at the interface. The separated electrons and holes can effectively participate in the redox reactions with water/pollutants to produce the photocatalytically reactive species superoxide ions (·O2−) and hydroxyl radicals (·OH), respectively. This is consistent with the experimental results. It is also worth noting that the g-C3N4/BiOI (001) heterostructure shows a larger difference in the effective mass of carriers. Therefore, the direct Z-scheme charge transfer and separation mechanism and the larger effective mass difference of carriers lead to the superior photocatalytic activity of the g-C3N4/BiOI (001) in experiments. A few speculations and controversies that arose from the experiments are clarified.
The construction of multiple continuous fully substituted carbon centers, which serve as unique structural motif in natural products, is a challenging topic in organic synthesis. Herein, we report a ...hydrated 3+2 cyclotelomerization of butafulvenes to create contiguous fully substituted carbon backbone. In the presence of scandium triflate, all‐carbon skeleton with spiro fused tricyclic ring can be constructed in high diastereoselectivity by utilizing butafulvene as the synthon. Mechanistic studies suggest that this atom‐economic reaction probably proceeds through a synergistic process containing butafulvenes dimerization and nucleophilic attack by water. In addition, the tricyclic product can undergo a series of synthetic derivatizations, which highlights the potential applications of this strategy. The recyclability of Sc(OTf)3 has also been demonstrated to show its robust performance in this hydrated cyclotelomerization.
A hydrated 3+2 cyclotelomerization of butafulvenes has been developed to create spiro fused tricyclic rings with a contiguous fully substituted carbon motif.
Bridged benzazepine scaffolds, possessing unique structural and physicochemical activities, are widespread in various natural products and drugs. The construction of these skeletons often requires ...elaborate synthetic effort with low efficiency. Herein, we develop a simple and divergent approach for constructing various bridged benzazepines by a photocatalytic intermolecular dearomatization of naphthalene derivatives with readily available α‐amino acids. The bridged motif is created via a cascade sequence involving photocatalytic 1,4‐hydroaminoalkylation, alkene isomerization and cyclization. Interestingly, the diastereoselectivity can be regulated through different reaction modes in the cyclization step. Moreover, aminohydroxylation and its further bromination have also been demonstrated to access highly functionalized bridged benzazepines. Preliminary mechanistic studies have been performed to get insights into the mechanism. This method provides a divergent synthetic approach for construction of highly functionalized bridged benzazepines, which have been otherwise difficult to access.
A mild and efficient protocol is developed to convert simple aromatic substrates into value‐added and structurally complex bridged benzazepines via a photocatalytic dearomatization. The switchable diastereoselectivity could be furnished by the manipulation of base‐promoted or photoinduced intramolecular hydroamination.
The big data era of “data-driven schools, educational analytics and transformation” has arrived and information technology has emerged in education. As the social demand for English writing in ...universities increases, the research of English writing becomes important, and the use and study of big data and information will only become the new standard for teaching and learning English. This study uses the GBDT model to extract and analyze teaching materials prepared by an English university writing skills course, select materials tailored to students’ characteristics, and produce student test scores. Learning models for predicting, analyzing and analyzing students’ writing scores, information technology can accurately predict students’ scores, which ensures the correct use of information technology in English university academic writing and the impact of GBDT. model for predicting outcomes, which has a positive role and value in student academic writing and teacher training.
High temperatures have a great impact on plant reproductive development and subsequent fruit and seed set, but the underlying molecular mechanisms are not well understood. We used transcriptome ...profiling to investigate the effect of heat stress on reproductive development of Arabidopsis thaliana plants and observed distinct response patterns in vegetative versus reproductive tissues. Exposure to heat stress affected reproductive developmental programs, including early phases of anther/ovule development and meiosis. Also, genes participating in the unfolded protein response (UPR) were enriched in the reproductive tissue-specific genes that were upregulated by heat. Moreover, we found that the UPR-deficient bzip28 bzip60 double mutant was sensitive to heat stresses and had reduced silique length and fertility. Comparison of heat-responsive wild type versus bzip28 bzip60 plants identified 521 genes that were regulated by bZIP28 and bZIP60 upon heat stress during reproductive stages, most of which were noncanonical UPR genes. Chromatin immunoprecipitation coupled with high-throughput sequencing analyses revealed 133 likely direct targets of bZIP28 in Arabidopsis seedlings subjected to heat stress, including 27 genes that were also upregulated by heat during reproductive development. Our results provide important insights into heat responsiveness in Arabidopsis reproductive tissues and demonstrate the protective roles of the UPR for maintaining fertility upon heat stress.
The ubiquitin conjugating enzyme E2 N (UBE2N) has been reported to be involved in the tumorigenesis of several tumors, but its function in cervical carcinoma has not been investigated yet. In the ...present study, UBE2N was found elevated in cervical carcinoma, and patients with high UBE2N had a shorter overall survival than patients with low expression. Additionally, knockdown of UBE2N decreased the activation of MEK1/2 and p38 in cervical carcinoma cells, and UBE2N knockdown also markedly inhibited cervical carcinoma cell growth. Our further studies found that microRNA‐590‐3p (miR‐590‐3p) was significantly decreased in cervical carcinoma, and patients with high miR‐590‐3p had a longer overall survival than patients with low expression. Moreover, miR‐590‐3p expression was found negatively correlated with UBE2N expression in cervical carcinoma, and our further studies showed that miR‐590‐3p targeted UBE2N and inhibited its expression in cervical carcinoma. Overexpression of miR‐590‐3p could inhibit cervical carcinoma cell growth, but enhanced UBE2N could rescue miR‐590‐3p‐induced cell growth inhibition in cervical carcinoma. This study indicated that targeting miR‐590‐3p/UBE2N axis could be a potential strategy for the treatment of cervical carcinoma.
Environmental stress from climate change and agricultural activity threatens global plant biodiversity as well as crop yield and quality. As sessile organisms, plants must maintain the integrity of ...their genomes and adjust gene expression to adapt to various environmental changes. In eukaryotes, nucleosomes are the basic unit of chromatin around which genomic DNA is packaged by condensation. To enable dynamic access to packaged DNA, eukaryotes have evolved Snf2 (sucrose nonfermenting 2) family proteins as chromatin remodeling factors (CHRs) that modulate the position of nucleosomes on chromatin. During plant stress responses, CHRs are recruited to specific genomic loci, where they regulate the distribution or composition of nucleosomes, which in turn alters the accessibility of these loci to general transcription or DNA damage repair machinery. Moreover, CHRs interplay with other epigenetic mechanisms, including DNA methylation, histone modifications, and deposition of histone variants. CHRs are also involved in RNA processing at the post‐transcriptional level. In this review, we discuss major advances in our understanding of the mechanisms by which CHRs function during plants’ response to environmental stress.
Chromatin‐remodeling factors are Snf2 family ATPases that compress and decompress nucleosome‐packaged DNA, making it accessible for DNA replication, DNA repair, and selective gene expression. This review summarizes recent advances on the mechanisms by which chromatin‐remodeling factors function during plant responses to environmental stress.
Cluster states, whose model are a remarkably rich structure in measurement-based quantum computation, hold high degree of entanglement, while entanglement is very fragile during the process of ...transmission because of the inevitable interaction with the environment. We propose two entanglement concentration protocols for four-particle linear cluster states which and are susceptible to the decoherence and the imperfect communication setups. In the first protocol, POVM operators are introduced to maximize the success probability, and the second protocol is based on cross-Kerr nonlinearity which is utilized to check the parity between the original particle and the ancillary particle. Both of the protocols have their own advantages. The first one can be easily realized in experiment by linear optics, while the one with cross-Kerr nonlinearity reach more than 90% success probability by iteration. Since the wide application of cluster states, the two protocols are efficient and valuable to different fields of quantum communication.
Abstract
As a large number of organic compounds possessing two isoprene units, monoterpenes and monoterpenoids play important roles in pharmaceutical, cosmetic, agricultural, and food industries. In ...nature, monoterpenes are constructed from geranyl pyrophosphate (C10) via various transformations. Herein, the bulk C5 chemical—isoprene, is used for the creation of various monoterpenoids via a nucleophilic aromatization of monoterpenes under cascade catalysis of nickel and iodine. Drugs and oil mixtures from conifer and lemon can be convergently transformed to the desired monoterpenoid. Preliminary mechanistic studies are conducted to get insights about reaction pathway. Two types of cyclic monoterpenes can be respectively introduced onto two similar heterocycles via orthogonal C–H functionalization. And various hybrid terpenyl indoles are programmatically assembled from abundant C5 or C10 blocks. This work not only contributes a high chemo-, regio-, and redox-selective transformation of isoprene, but also provides a complementary approach for the creation of unnatural monoterpenoids.
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