Chiral tertiary alcohols are an important class of organic compounds which have found wide applications in both academia and industry. Therefore, various synthetic strategies towards these compounds ...have already been developed. Among them, the catalytic asymmetric addition of carbon nucleophiles to ketones is the most desirable route owing to its straightforwardness as well as its economic, efficient and versatile advantages. This review summarizes and discusses the recent achievements in this field classified according to the reaction types. Special attention is paid to the mechanisms, advantages and limitations of each reaction. In addition, the applications of these catalytic processes in the synthesis of related natural products, pharmaceuticals or their analogues are briefly discussed as well.
The 3,3′‐disubstituted oxindole structural motif is a prominent feature in many alkaloid natural products, which include all kinds of tetrasubstituted carbon stereocenters, spirocyclic or not, ...all‐carbon or heteroatom‐containing. The catalytic asymmetric synthesis of the tetrasubstituted carbon stereocenter at the C‐3 position of the oxindole framework integrates new synthetic methods and chiral catalysts, reflects the latest achievements in asymmetric catalysis, and facilitates the synthesis of sufficient quantities of related compounds as potential medicinal agents and biological probes. This review summarizes the recent progress in this area, and applications in the total synthesis of related bioactive compounds.
A remarkable fluorine effect on “on water” reactions is reported. The CF⋅⋅⋅HO interactions between suitably fluorinated nucleophiles and the hydrogen‐bond network at the phase boundary of oil ...droplets enable the formation of a unique microstructure to facilitate on water catalyst‐free reactions, which are difficult to realize using nonfluorinated substrates. Accordingly, a highly efficient on water, catalyst‐free reaction of difluoroenoxysilanes with aldehydes, activated ketones, and isatylidene malononitriles was developed, thus leading to the highly efficient synthesis of a variety of α,α‐difluoro‐β‐hydroxy ketones and quaternary oxindoles.
It's on! The CF⋅⋅⋅HO interactions between suitably fluorinated nucleophiles and a hydrogen‐bond network at the phase boundary of an oil droplet facilitate “on water” catalyst‐free reactions. Accordingly, the title reaction of difluoroenoxysilanes with aldehydes, activated ketones, and isatylidene malononitriles was developed, thus leading to α,α‐difluoro‐β‐hydroxy ketones and quaternary oxindoles.
This review summarizes the advances in the catalytic enantioselective construction of vicinal quaternary carbon stereocenters, introduces major synthetic strategies and discusses their advantages and ...limitations, highlights the application of known protocols in the total synthesis of natural products, and outlines the synthetic opportunities.
This review summarizes the advances in catalytic enantioselective construction of vicinal quaternary carbon stereocenters, introduces major synthetic strategies and discusses their advantages and limitations, and outlines the synthetic opportunities.
Graphitic carbon nitride (g-C3N4) is first explored in the application of energy capture by taking advantage of strong piezoelectricity derived from intrinsically non-centrosymmetric holes, leading ...to in-plane piezoelectricity even in multilayers or bulk structures. In the present work, we demonstrate the successful fabrication and efficient energy harvesting of g-C3N4-based piezoelectric nanogenerators (PENGs), where a several-fold enhancement of output performance is achieved by modulating precursors through tuning the intrinsic lattice strain and crystallinity of g-C3N4. Specifically, the best output voltage and a current density up to 1672 mV and 141 nA/cm2 are obtained from piezoelectric g-C3N4 synthesized using blended precursors of urea and melamine. This work sheds light on the investigation of g-C3N4-based PENGs for energy harvesting. There is clearly potential to develop multifunctional self-powered g-C3N4-based devices by combining the excellent optoelectronic, piezoelectric, and mechanical properties of g-C3N4.
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•Graphitic carbon nitride (g-C3N4) is first explored in the application of energy capture.•We demonstrate the successful fabrication and efficient energy harvesting of g-C3N4-based PENGs.•A several-fold enhancement of performance is achieved by tuning the intrinsic lattice strain and crystallinity of g-C3N4.
Indole derivatives are important heterocycles in organic synthesis for serving as privileged building blocks for functional material and as key components in a lot of bioactive compounds. Propargylic ...alcohols, bearing alkynyl and hydroxyl functional groups, have emerged as promising feedstock materials for the construction of carbo‐ and heterocycles. Especially, in the last decade, the Lewis or Brønsted acid catalysed tandem annulations of propargylic alcohols to build structurally diverse indole derivatives have been well‐investigated. In this review, we summarize two main synthetic strategies toward indole derivatives via the cascade reactions of propargylic alcohols: indole‐ring formation involved tandem reactions and the direct function‐alization of indole skeletons. We hope this review would help to develop new and more efficient protocols for the synthesis of indole‐included N‐heterocycles.
In order to solve the problems of the same target importance and too large solution set in the existing solutions, an E-dominant NSGA2 algorithm is proposed to solve the problem. In this paper, the ...mathematical model of the problem is established with the optimization objectives of test cost, test quantity and false alarm rate. The testability model under unreliable test condition is established by using Bayesian network. Then the E-dominated NSGA2 algorithm is used to solve the problem. After verification, the algorithm has good performance and practical value.
Automatic modulation classification (AMC) plays an important role in both civilian and military applications. Today, increasingly more researchers apply a deep learning framework in AMC. However, few ...papers take into account that a typical deep model is difficult to deploy on resource constrained devices. In this paper, we propose a new filter-level pruning technique based on activation maximization (AM) that omits the less important convolutional filter. Compared to other network pruning techniques, the convolutional neural network pruned via the AM method achieves equal or higher classification accuracy in the RadioML2016.10a dataset.
Test configuration optimization is an important part in the process of testability design. In order to be close to the reality, this paper chooses to carry out the test optimization selection under ...the condition of unreliable test. Under this condition, Test configuration optimization is essentially a multi-objective optimization problem. Therefore, this paper establishes a mathematical model of the problem with test cost, test quantity and false alarm rate as optimization objectives. In this paper, the multi-objective particle swarm optimization algorithm and NSGA2 algorithm are comprehensively analyzed. According to the advantages and disadvantages of the two algorithms, NSGA2-MOPSO algorithm is proposed to solve the test optimization selection problem. The results show that the NSGA2-MOPSO algorithm has good performance and high practicability.
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