Catalytic enantioselective construction of all-carbon quaternary stereocenters, i.e. carbon atoms bearing four different carbon substituents, poses a particular challenge in organic synthesis. This review gives a comprehensive account on the currently available methods of the above transformation that afford high enantioselectivities and synthetically useful yields.

A three-dimensional (3D) graphene foam (GF)/poly(dimethylsiloxane) (PDMS) composite was fabricated by infiltrating PDMS into 3D GF, which was synthesized by chemical vapor deposition (CVD) with nickel foam as template. The electrical properties of the GF/PDMS composite under bending stress were investigated, indicating the resistance of the GF/PDMS composite was increased with the bending curvature. To improve the bending sensitivity of the GF/PDMS composite, a thin layer of poly(ethylene terephthalate) (PET) was introduced as substrate to form double-layer GF/PDMS-PET composite, whose measurements showed that the resistance of the GF/PDMS-PET composite was still increased when bended to the side of PET, whereas its resistance would be decreased when bended to the side of GF. For both cases, the absolute value of the relative variation of electrical resistance was increased with the bending curvature. More importantly, the relative variation of electrical resistance for double-layer GF/PDMS-PET composite can be up to six times higher than single-layer GF/PDMS composite for the same bending curvature. These observations were further supported by the principle of mechanics of material. The 3D GF/PDMS-PET composite also has higher flexibility and environment stability and can be utilized as a strain sensor with high sensitivity, which can find important applications in real-time monitoring of buildings, such as a bridge, dam, and high-speed railway.

Nanostructured Co3O4 materials attracted significant attention due to their exceptional electrochemical (pseudo-capacitive) properties. However, rigorous preparation conditions are needed to control the size (especially nanosize), morphology and size distribution of the products obtained by conventional methods. Herein, we describe a novel one step shape-controlled synthesis of uniform Co3O4 nanocubes with a size of 50 nm with the existence of mesoporous carbon nanorods (meso-CNRs). In this synthesis process, meso-CNRs not only act as a heat receiver to directly obtain Co3O4 eliminating the high-temperature post-calcination, but also control the morphology of the resulting Co3O4 to form nanocubes with uniform distribution. More strikingly, mesoporous Co3O4 nanocubes are obtained by further thermal treatment. The structure and morphology of the samples were characterized by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. A possible formation mechanism of mesoporous Co3O4 nanocubes is proposed here. Electrochemical tests have revealed that the prepared mesoporous Co3O4 nanocubes demonstrate a remarkable performance in supercapacitor applications due to the porous structure, which endows fast ion and electron transfer.

No abstract

The first enantioselective aza-Darzens reaction of cyclic imines with a-halogenated ketones was realized under mild reaction conditions by using amino-acid-derived bifunctional phosphonium salts as phase-transfer promoters.A variety of structurally dense tri-and tetrasubstituted aziridine derivatives,c ontaining benzofused heterocycles as well as spiro-structures,w ere readily synthesized in high yields with excellent diastereo-and enantioselectivities (up to > 20:1 d.r. and > 99.9 %ee). The highly functionalizedaziridine products could be easily transformed into different classes of biologically active compounds.Optically pure fused N-heterocycles,e specially aziridinecontaining molecules,are versatile intermediates in chemical synthesis, [1] and they are also prevalent building blocks in many biologically active compounds,i ncluding natural alkaloids and pharmaceutical agents (Scheme 1). [2] Accordingly, an umber of catalytic methods have been devised for the stereoselective construction of such structural motifs over the past two decades. [3][4][5][6][7][8][9] In this context, the aza-Darzens reaction becomes one of the most straightforward and efficient approaches for producing such ring systems. [5] Lewis and Brønsted acid catalyzed aza-Darzens of a-diazoacetates and imines,offering aziridines,were first disclosed by Brookhart, Te mpleton, and co-worker. [6] Thea symmetric variants of these acid-catalyzed aza-Darzens reactions were first reported by Wulff and co-workers [7] and further developed by Maruoka and co-workers, [8] and others, [9] particularly providing cis-o r/and trans-disubstituted aziridines in high yields with excellent stereoselectivities.However,less success has been achieved in direct construction of trisubstituted chiral aziridine scaffolds by this process,a nd only two examples were reported. [10] Maruoka and co-workers dis-closed achiral Brønsted acid catalyzed aziridination between N-a-diazoacylo xazolidinones and N-Boc imines,t hus creating trisubstituted chiral aziridine skeletons. [10a] Quite recently, Tr ost developed aZ n-ProPhenol catalyzed aza-Darzens reaction of chlorinated aromatic ketones with N-Boc aldimines,p roviding an ovel method for constructing trisubstituted chiral aziridine motifs. [10b] Although these impressive advances have been made,h ighly enantioselective preparation of trisubstituted aziridine rings is still synthetically challenging,let alone direct asymmetric synthesis of structurally dense tetrasubstituted chiral aziridine molecules.T ot he best of our knowledge,n og eneral and straightforward catalytic protocol to access optically pure tetrasubstituted aziridines has been reported so far. Therefore,i ti sh ighly desirable to explore autilitarian strategy to fill this void.In this study,w ea ttempted to develop an alternative approach to prepare structurally dense tri-and tetrasubstituted aziridines with readily available catalysts and reagents. In the past decades,a symmetric phase-transfer catalysis (PTC) has been recognized as ap owerful and versatile...

Asymmetric visible-light photocatalysis has recently drawn considerable attention of the scientific community owing to its unique activation modes and significance for the enantioselective green synthesis.

A methodology to assemble the azaanthraquinone skeleton from N-propargylamino quinone by a Au(I)-catalyzed 6-endo-dig cycloisomerization was developed. The catalytic process was applied to the synthesis of alkaloid cleistopholine and its analogues. A mechanism involving benign nucleophilicity of the aminoquinone was proposed.

A palladium-catalyzed asymmetric allylic alkylation effects a dynamic kinetic asymmetric transformation of racemic isoprene monoepoxide and a surrogate for Nazarov's reagent in which a quaternary center is created with exellent ee. The resultant adduct allows easy access to a substrate for ring-closing metathesis to form a cyclopentenone and sets the stage for an 11-step synthesis of the cyclopentyl core of the antibiotic antitumor agent viridenomycin. [reaction: see text]