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.
Chiral transient directing group (cTDG) strategies give rise to fundamentally new concepts in asymmetric C−H activation and enable the synthesis of chiral molecules without the need of pre‐installation and removal of directing groups. This Minireview provides an overview of recent advances in cTDG for the construction of chiral compounds with different types of chirality.
Improving the reactivity and selectivity is a long pursuing goal in C—H functionalization reactions. In line with this goal, a well‐designed bidentate 2‐(pyridine‐yl)isopropyl amine (PIP amine) ...directing group was developed by our group to achieve the activation of unbiased methylene C(sp3)–H activation, which also found its broad applications in C—H activation reactions catalyzed by base metals, such as Cu, Ni, Co and Fe, to form various C—C and C—X bonds. Moreover, PIP amine has also been applied in the strategic step toward the total synthesis of aeruginosin marine natural products. Its highly tunable structure has triggered the design of a series of chiral auxiliaries for diastereoselective C—H activation. More recently, Pd(II)‐catalyzed enantioselective functionalization of unbiased methylene C(sp3)–H bonds enabled by the cooperative effects between PIP amine and chiral ligands with axially chiral binaphthyl scaffold has also been realized. In this account, we briefly summaries the journey of developing PIP amine for C—H activation, from controlling the reactivity and regioselectivity to stereoselectivity.
The journey of developing PIP amine auxiliary for C—H activation, from controlling the reactivity and regioselectivity to stereoselectivity.
Zika virus (ZIKV) was once considered an obscure member of the large and diverse family of mosquito-borne flaviviruses, and human infections with ZIKV were thought to be sporadic, with mild and ...self-limiting symptoms. The large-scale ZIKV epidemics in the Americas and the unexpected uncovering of a link to congenital birth defects escalated ZIKV infections to the status of a global public health emergency. Recent studies that combined reverse genetics with modelling in multiple systems have provided evidence that ZIKV has acquired additional amino acid substitutions at the same time as congenital Zika syndrome and other birth defects were detected. In this Progress article, we summarize the evolution of ZIKV during its spread from Asia to the Americas and discuss potential links to pathogenesis.
A clear understanding of long-term bio-hydro-thermo-mechanical (BHTM) behaviors of landfilled Municipal Solid Waste (MSW) is essential to better design and manage landfills, which requires the ...development of both analytical and numerical models that can represent typical behaviors of MSW. In this study, a novel multi-phase, multi-component numerical model, which incorporated the diffusion of landfill gas components, changes in the pH of leachate, and its solute migration as well as phase changes, was presented and adopted to investigate long-term coupled behaviors of MSW and the spatial and temporal variations of MSW properties. The numerical simulations were conducted on a typical landfill column and a landfill slope with relatively clear initial and boundary conditions to explore the coupled BHTM interactions of landfilled MSW. Based on the simulation results, the coupled mechanisms of MSW biodegradation, leachate and gas flows, MSW deformation, and heat transfer were revealed, and some significant insights on qualities of both leachate and landfill gas were also given. It has been found that the coupled model associated with its numerical code successfully predicted the long-term behaviors of landfilled MSW and qualities of leachate and landfill gas.
•Mathematical formulations for coupled processes in landfills are given.•Each process in landfills is interpreted in detail with different sub-models.•The existing models for simulating coupled MSW ...behaviors are summarized.•Challenges and perspectives for modeling coupled behaviors of MSW are discussed.
Landfilling is the primary method used for municipal solid waste (MSW) disposal. To design, optimize, and manage landfills with a life span of several decades, a deeper understanding of long-term MSW behaviors is necessary and worthwhile. These behaviors should be modeled using approaches that account for coupled processes so as to capture the evolutionary mechanisms that are mainly dominated by biochemical, mechanical, hydraulic, and thermal processes, as well as the complex interactions among them. Many mathematical models have been developed over the past three decades to address this issue. However, most of them only emphasize some of these processes, with only few models accounting for all the processes. In this review, we present a comprehensive overview of the mathematical and numerical formulations of this coupled problem. Each process occurring in landfills is interpreted in detail using different sub-models and the corresponding parameter values. Then, the existing coupled models for MSW are reviewed, and the challenges and perspectives related to the modeling of the long-term behaviors of MSW are highlighted. We conclude that more reliable constitutive formulations based not only on well-designed laboratory tests but also on field tests are necessary to improve the modeling of MSW behaviors in future.
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(sp
)-H bonds
larger-membered metallacycles. Recent development to achieve remote C(sp
)-H functionalization
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(sp
)-H bonds.
Rational design of non‐noble metal catalysts with robust and durable electrocatalytic activity for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction ...(HER) is extremely important for renewable energy conversion and storage, regenerative fuel cells, rechargeable metal–air batteries, water splitting etc. In this work, a unique hybrid material consisting of Fe3C and Co nanoparticles encapsulated in a nanoporous hierarchical structure of N‐doped carbon (Fe3C‐Co/NC) is fabricated for the first time via a facile template‐removal method. Such an ingenious structure shows great features: the marriage of 1D carbon nanotubes and 2D carbon nanosheets, abundant active sites resulting from various active species of Fe3C, Co, and NC, mesoporous carbon structure, and intimate integration among Fe3C, Co, and NC. As a multifunctional electrocatalyst, the Fe3C‐Co/NC hybrid exhibits excellent performance for ORR, OER, and HER, outperforming most of reported triple functional electrocatalysts. This study provides a new perspective to construct multifunctional catalysts with well‐designed structure and superior performance for clean energy conversion technologies.
A hybrid material of Fe3C‐Co/NC is synthesized through a facile template‐removal method, where Fe3C and Co nanoparticles are encapsulated in a nanoporous N‐doped hierarchical structure integrating 1D carbon nanotubes and 2D carbon nanosheets. As a multifunctional electrocatalyst, such a hybrid exhibits superior catalytic performances for oxygen reduction reaction, oxygen evolution reaction and hydrogen evolution reaction simultaneously.
Atroposelective synthesis of axially chiral biaryls by palladium‐catalyzed C−H olefination, using tert‐leucine as an inexpensive, catalytic, and transient chiral auxiliary, has been realized. This ...strategy provides a highly efficient and straightforward access to a broad range of enantioenriched biaryls in good yields (up to 98 %) with excellent enantioselectivities (95 to >99 % ee). Kinetic resolution of trisubstituted biaryls bearing sterically more demanding substituents is also operative, thus furnishing the optically active olefinated products with excellent selectivity (95 to >99 % ee, s‐factor up to 600).
No attachements: The title reaction employs tert‐leucine as a transient chiral auxiliary and provides efficient access to enantioenriched biaryls in good yields (up to 98 %) with excellent enantioselectivities (up to >99 % ee). Kinetic resolution of trisubstituted biaryls bearing sterically more demanding substituents is also operative, thus furnishing the optically active olefinated products with excellent selectivity (up to >99 % ee, s‐factor up to 600).
The discovery of proper ligands to simultaneously modulate the reactivity and effectively control the stereoselectivity is a central topic in the field of enantioselective C−H activation. Herein, we ...reported the synthesis of axially chiral biaryls by Pd‐catalyzed atroposelective C−H olefination. A novel chiral spiro phosphoric acid, STRIP, was identified as a superior ligand for this transformation. A broad range of axially chiral quinoline derivatives were synthesized in good yields with excellent enantioselectivities (up to 98 % ee). Density functional theory was used to gain a theoretical understanding of the enantioselectivities in this reaction.
The discovery of proper ligands to simultaneously modulate the reactivity and effectively control the stereoselectivity is a central topic in the field of enantioselective C−H activation. Herein, the synthesis of axially chiral biaryls by Pd‐catalyzed atroposelective C−H olefination is reported. A broad range of axially chiral quinoline derivatives were synthesized in good yields with excellent enantioselectivities (up to 98 % ee).
Transition-metal-catalyzed, coordination-assisted C(sp
)-H functionalization has revolutionized synthetic planning over the past few decades as the use of these directing groups has allowed for ...increased access to many strategic positions in organic molecules. Nonetheless, several challenges remain preeminent, such as the requirement for high temperatures, the difficulty in removing or converting directing groups, and, although many metals provide some reactivity, the difficulty in employing metals outside of palladium. This review aims to give a comprehensive overview of coordination-assisted, transition-metal-catalyzed, direct functionalization of nonactivated C(sp
)-H bonds by covering the literature since 2004 in order to demonstrate the current state-of-the-art methods as well as the current limitations. For clarity, this review has been divided into nine sections by the transition metal catalyst with subdivisions by the type of bond formation. Synthetic applications and reaction mechanism are discussed where appropriate.
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