Palladium-catalyzed ortho-C–H silylation of biaryl aldehydes using a transient directing group

A strategy for Pd-catalyzed ortho-C–H silylation of biaryl aldehydes enabled by a transient auxiliary is presented. This protocol provides a broad range of ortho-silylated biaryl aldehydes in good yields. The silyl moiety can be further functionalized under mild conditions, rendering the silylated products useful building blocks. Notably, this protocol also offers an opportunity to establish a platform for expeditious synthesis of structurally diverse axially chiral biaryl aldehydes via sequential atroposelective interannular C–H functionalization/intraanular C–H silylation.     

Synthesis of Axially Chiral Styrenes through Pd-Catalyzed Asymmetric C−H Olefination Enabled by an Amino Amide Transient Directing Group

The atroposelective synthesis of axially chiral styrenes remains a formidable challenge due to their relatively lower rotational barriers compared to the biaryl atropoisomers. Herein, we describe the construction of axially chiral styrenes through Pd^II-catalyzed atroposelective C−H olefination, using a bulky amino amide as a transient chiral auxiliary. Various axially chiral styrenes were produced with good yields and high enantioselectivity (up to 95 % yield and 99 % ee). Carboxylic acid derivatives of the resulting axially chiral styrenes showed superior enantiocontrol over the biaryl counterparts in Co^III-catalyzed enantioselective C(sp³)−H amidation of thioamide. Mechanistic studies suggest that C−H cleavage is the enantioselectivity-determining step.     

Transition Metal-Catalyzed Enantioselective C−H Functionalization via Chiral Transient Directing Group Strategies

Transition metal-catalyzed enantioselective functionalization of C−H bond, the most abundant functionality in organic molecules, has emerged as an expedient synthetic approach to streamline the synthesis of complex chiral molecules. Despite significant progress, traditional directing group-enabled strategies require additional steps for the installation and removal of directing groups from the target molecule. The recently developed asymmetric C−H functionalization using chiral transient directing groups (cTDGs) offers a promising alternative that can circumvent this obstacle and therefore simplify the process. In this Minireview, we briefly discuss the advent and recent advances of this emerging concept, with an emphasis on discussing the creation of various stereogenic centers and the developments of cTDGs. Applications in natural product synthesis and ligand derivatizations are also discussed. We hope this Minireview will highlight the great potential of this strategy and help to inspire further endeavors.     

The computations of reflection coefficients of multilayer structure based on the reformulation of Thomson-Haskell method

A reformulation of the Thomson-Haskell method is presented for calculating the reflection coefficients of multilayer structure immersing in the coupling fluid. Instead of directly multiplying the layer propagator matrix, the new method splits the layer propagator matrix and excursively determines the interface stiffness matrix starting from the bottom half-space with known stiffness. A formulation for the reflection coefficients is derived based on the obtained interface stiffness matrix of the top layer. This scheme can be applied to a single solid layers or layered structures containing both fluid and solid layers. It keeps the simplicity but naturally excludes the exponential growth term and thus can be applied at any frequency range. Its validity and feasibility were experimentally proved by the measurement of the reflection coefficients of a three layered structure of aluminum–glass–aluminum and a sandwiched layer structure of two 250 μm stainless plates filled with 100 μm deionized water based on the inversion of V(z, t) technique. The result of experiments is consistent with the theoretical calculation. The reformulation of the Thomson-Haskell method offers an efficient and effective solution for calculating the acoustic reflection coefficients of multilayer structures of any configurations.     

Site-selective functionalization of remote aliphatic C–H bonds via C–H metallation

Directing group assistance provided a paradigm for controlling site-selectivity in transition metal-catalyzed C–H functionalization reactions. However, the kinetically and thermodynamically favored formation of 5-membered metallacycles has greatly hampered the selective activation of remote C(sp³)–H bonds via larger-membered metallacycles. Recent development to achieve remote C(sp³)–H functionalization via the C–H metallation process largely relies on employing specific substrates without accessible proximal C–H bonds. Encouragingly, recent advances in this field have enabled the selective functionalization of remote aliphatic C–H bonds in the presence of equally accessible proximal ones by taking advantage of the switch of the regiodetermining step, ring strain of metallacycles, multiple non-covalent interactions, and favourable reductive elimination from larger-membered metallacycles. In this review, we summarize these advancements according to the strategies used, hoping to facilitate further efforts to achieve site- and even enantioselective functionalization of remote C(sp³)–H bonds.

Recent advances in site-selective functionalization of remote aliphatic C–H bonds in organometallic pathways are summarized.     

Atroposelective synthesis of N-aryl peptoid atropisomers via a palladium(ii)-catalyzed asymmetric C–H alkynylation strategy

The introduction of chirality into peptoids is an important strategy to determine a discrete and robust secondary structure. However, the lack of an efficient strategy for the synthesis of structurally diverse chiral peptoids has hampered the studies. Herein, we report the efficient synthesis of a wide variety of N-aryl peptoid atropisomers in good yields with excellent enantioselectivities (up to 99% yield and 99% ee) by palladium-catalyzed asymmetric C–H alkynylation. The inexpensive and commercially available l-pyroglutamic acid was used as an efficient chiral ligand. The exceptional compatibility of the C–H alkynylation with various peptoid oligomers renders this procedure valuable for peptoid modifications. Computational studies suggested that the amino acid ligand distortion controls the enantioselectivity in the Pd/l-pGlu-catalyzed C–H bond activation step.

The introduction of chirality into peptoids is an important strategy to determine a discrete and robust secondary structure.     

Two new cadmium(II) coordination polymers based on imidazole‐containing ligands: synthesis,structural characterization and fluorescence properties

The judicious selection of suitable ligands is vitally important in the construction of novel metal–organic frameworks (MOFs) with fascinating structures and interesting properties. Recently, imidazole‐containing multidentate ligands have received much attention. Two new Cd^II coordination frameworks, namely, poly[tris{μ‐1,4‐bis[(1H‐imidazol‐1‐yl)methyl]benzene‐κ²N³:N^3′}tetrakis(nitrato‐κ²O,O′)dicadmium], [Cd₂(NO₃)₄(C₁₄H₁₄N₄)₃]_n, (I), and poly[[bis{μ₃‐1,3,5‐tris[(1H‐imidazol‐1‐yl)methyl]benzene‐κ³N³:N^3′:N^3′′}cadmium] hexafluorosilicate], {[Cd(C₁₈H₁₈N₆)₂](SiF₆)}_n, (II), have been synthesized and characterized by elemental analysis, IR spectroscopy and single‐crystal X‐ray diffraction. In polymer (I), the 1,4‐bis[(1H‐imidazol‐1‐yl)methyl]benzene ligand bridges Cd²⁺ ions with a distorted seven‐coordinated pentagonal bipyramidal geometry, forming a one‐dimensional ladder chain, and the nitrate anions coordinate to the Cd²⁺ ions in a terminal bidentate fashion. In the crystal, adjacent chains are further connected by C—H…O hydrogen bonds to generate a two‐dimensional (2D) supramolecular structure. Polymer (II) exhibits a 2D layered structure in which 1,3,5‐tris[(1H‐imidazol‐1‐yl)methyl] benzene ligands join Cd²⁺ centres having a six‐coordinated octahedral structure. The layers are connected by hexafluorosilicate anions via C—H…F hydrogen‐bond interactions, giving rise to a three‐dimensional supramolecular network structure in the solid state. In addition, powder X‐ray diffraction (PXRD) patterns were recorded, thermogravimetric analyses (TGA) carried out and fluorescence properties investigated.     

Peppermint oil decreases the production of virulence-associated exoproteins by Staphylococcus aureus

The present study aimed to evaluate the antimicrobial activity of peppermint oil against Staphylococcus aureus, and further investigate the influence of peppermint oil on S. aureus virulence-related exoprotein production. The data show that peppermint oil, which contained high contents of menthone, isomenthone, neomenthol, menthol, and menthyl acetate, was active against S. aureus with minimal inhibitory concentrations (MICs) ranging from 64-256 μg/mL, and the production of S. aureus exotoxins was decreased by subinhibitory concentrations of peppermint oil in a dose-dependent manner. The findings suggest that peppermint oil may potentially be used to aid in the treatment of S. aureus infections.