Conspectus Directing group (DG) assistance provides a good solution to the problems of reactivity and selectivity, two of the fundamental challenges in C(sp3)–H activation. However, the activation ...of unbiased methylene C(sp3)–H bonds remains challenging due to the high heterolytic bond dissociation energy and substantial steric hindrance. Two main strategies have been developed thus far, that is, use of a strongly coordinating bidentate DG pioneered by Daugulis and use of a weakly coordinating monodentate DG accelerated by pyridine-type ligands, as disclosed by Yu. The seminal work by Daugulis sparked significant interest in the application of the monoanionic bidentate auxiliary in aliphatic C–H activation reactions. Our research has focused on enabling the divergent functionalization and enantiotopic differentiation of unactivated methylene C–H bonds. Inspired by the structure of bidentate 8-aminoquinoline and the accelerating effect of the gem-dimethyl moiety in cyclometalations, we developed a strongly coordinating bidentate 2-(pyridine-yl)isopropyl (PIP) amine DG consisting of a pyridyl group, a gem-dimethyl moiety, and an amino group, which enabled the divergent functionalization of unactivated β-methylene C(sp3)–H bonds to forge C–O, C–N, C–C, and C–F bonds with palladium catalysts. The exclusive β-selectivity was ascribed to the preferential formation of kinetically favored 5,5-bicyclic palladacycle intermediates. DFT calculations revealed that the well-designed gem-dimethyl group was responsible for the lowered energy and compressed bite angle of the key transition state related to C–H cleavage. More recently, the combination of PIP amine with axially chiral ligands was found to promote asymmetric functionalization of unbiased methylene C(sp3)–H bonds, a challenging research topic in the area of C–H activation that remains to be addressed. Two different types of axially chiral ligands, namely, non-C 2-symmetric chiral phosphoric acids (CPAs) and 3,3′-disubstituted BINOLs, have been developed. The former enabled Pd(II)-catalyzed inter- and intramolecular arylation of unbiased methylene C(sp3)–H bonds with high enantioselectivity, whereas the latter promoted a series of asymmetric functionalization reactions, such as alkynylation, arylation, alkenylation/aza-Wacker cyclization, and intramolecular amidation. The unexpectedly high stereocontrol compared with other bidentate DGs might be attributable to steric communication between the ligand and gem-dimethyl moiety of PIP amine. Thus far, the combination of PIP amine DG with 3,3′-disubstituted BINOL ligands is arguably the most general strategy for asymmetric functionalization of unbiased methylene C(sp3)–H bonds. Finally, the ease of installation and removal of PIP under mild conditions and synthetic applications are described.
The construction of carbon-carbon bonds is a central tenet of modern synthetic chemistry. Metal-catalyzed C-H functionalization can serve as a particularly powerful tool for achieving carbon-carbon ...bond formation. This review summarizes the early adventures and recent advancements in catalytic transformation of unactivated C(sp
3
)-H bonds into C(sp
3
)-C(sp
3
) bonds. To date, three main strategies have emerged to enable this transformation, namely, metallocarbene-triggered C(sp
3
)-H alkylation, auxiliary-directed C(sp
3
)-H alkylation, and photo-induced C(sp
3
)-H alkylation. Compared with traditional cross-coupling reactions having both coupling partners activated with functional groups or base-promoted enolate chemistry, catalytic alkylation of unactivated C(sp
3
)-H bonds for C(sp
3
)-C(sp
3
) bond formation not only offers novel disconnections in retrosynthetic analysis, but also represents the future trend in green and atom-economic chemistry.
This review summarizes recent advancements in catalytic direct transformation of unactivated C(sp
3
)-H bonds into C(sp
3
)-C(sp
3
) bonds.
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.
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.
Chiral spirooxindoles are privileged heterocyclic motifs, which are widely found in natural alkaloids and pharmaceuticals. Moreover, the construction of chiral spiro-cyclic frameworks is a ...long-lasting challenge in organic synthesis. The past four years have witnessed significant developments in this field, and this feature article outlines the recent progress in the catalytic asymmetric synthesis of spirooxindoles, including the contributions of our group. The catalytic asymmetric construction of spirooxindoles has greatly benefited from the utilization of oxindole derivatives as starting materials, including isatin derivatives, methyleneindolinones, indolin-2-one derivatives and isatin-derived 3-indolylmethanols. This article is divided into sections according to the size and type of the generated spiro-ring fused at the C3-position of the oxindole core (from three-membered to seven-membered spiro-rings), and representative examples are given with illustrations. In addition, the enantioselective construction of bispirooxindole frameworks is also discussed in the last section.
The past four years have witnessed significant developments in the field of the catalytic asymmetric synthesis of spirooxindoles, and this feature article outlines the recent progress in this area, including the contributions of our group. This article is divided into sections according to the size and type of the generated spiro-ring fused at the C3-position of the oxindole core.
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.
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