Chem Catalysis最新文献

An outstanding challenge in the Pd-catalyzed functionalization of allylamines is the control of stereochemistry. Terminal alkenes preferentially undergo Heck-type reactions, while internal alkenes may undergo a mixture of Heck and C–H activation reactions that give mixtures of stereochemical products. In the case of unprotected allylamines, the challenge in achieving C–H activation is that facile in situ formation of Pd nanoparticles leads to preferential formation of trans rather than cis substituted products. In this study, we have demonstrated the feasibility of using mono-protected amino acid ligands as metal-protecting groups to prevent aggregation and reduction, allowing the selective synthesis of free cis-arylated allylamines. This method complements Heck-selective methods, allowing complete stereochemical control over the synthesis of cinnamylamines, an important class of amine that can serve as therapeutics directly or as advanced intermediates. To highlight the utility of the methodology, we have demonstrated rapid access to mu (γ) opioid receptor ligands.

Enantioenriched, substituted saturated heterocycles extensively occur in natural products, bioactive targets, and organic frameworks. Conventional tools for their synthesis often require engineered precursors that limit the flexibility of the synthetic routes and the diversity of target scaffolds. Therefore, the rapid and diverse synthesis of these heterocyclic molecules is highly desired yet challenging. Undoubtedly, the direct asymmetric functionalization of simple and readily accessible heterocyclic substrates represents one of the most straightforward and efficient solutions. Recently, innovative and modular strategies based on alkyl cross-coupling, directing-group-assisted C–H activation, photocatalytic hydrogen atom transfer (HAT), Heck reaction, and hydro- and difunctionalization have been designed to access chiral saturated heterocyclic motifs, paving the way for their more extensive utilization in future pharmaceuticals. In this perspective, recent progress in the preparation of chiral saturated heterocycles is outlined. How these innovations have enabled new levels of molecular selectivity, complexity, and practicality is also emphasized.

High-temperature solid oxide cells (SOCs) can be used as a practical alternative for generation of value-added chemicals and energy-intensive fuels. Here we (1) report a comparative summary of SOC applications and their different structures, (2) appraise fundamentals of SOC configurations and thermal dynamics for generation of chemicals, including H₂, CO, HCN, NO, C₆H₆, and C₁ and C₂ hydrocarbons, together with SOC coupling for generation of CH₄, CH₃OH and NH₃, and (3) assess current research to support future SOC research. We conclude that (1) SOCs can be used as an electrochemical refinery (e-refinery) for sustainable generation of chemicals and (2) because of high-temperature operation, SOCs are advantageous over low-temperature fuel cells and electrolyser technologies in terms of nonprecious metal catalysts, high efficiency, and high kinetics. Findings will be of benefit in practical design for SOCs as an e-refinery for generation of chemicals and, therefore, of wide interest to researchers and manufacturers.

Although enantioselective C−H silylation has progressed rapidly in recent years, little mechanistic information on these reactions is available, especially for C−H silylation with dihydrosilanes toward silicon-stereogenic silanes. Here, we report a thorough combined experimental and theoretical mechanistic study on the rhodium-/Josiphos-catalyzed intramolecular enantioselective C−H silylation of dihydrosilanes for the construction of silicon-stereogenic centers. A rhodium silyl dihydride complex was identified as the resting state in the catalytic cycle, which was generated via a facile silyl metal migration process. This key resting state was also synthesized and characterized by X-ray crystallographic analysis. Density functional theory calculations were conducted to elucidate the full picture of the mechanism and shed light on the origin of the observed enantioselectivity and the racemization process in the reaction. With the understanding of the mechanism, both enantioenriched tetraorganosilanes and monohydrosilanes could be synthesized with decent yields and enantiomeric excess, respectively.

The production of ammonia in a green, environmentally friendly, and sustainable way is crucial for human society. This perspective focuses on the combination of covalent/metal-organic framework (COF/MOF) substrates and single-atom catalysts to produce ammonia through artificial photocatalytic N₂ fixation reactions. The single-atom catalysts demonstrate high activity toward N₂ fixation due to the maximum atomic efficiency, while they are easy to aggregate. COFs/MOFs are crystalline and porous materials that offer suitable platforms to anchor single atoms. Furthermore, the photoelectrochemical properties and local coordination environments are precisely controlled by tuning the structures of COF/MOF substrates, leading to high activity for the NH₃ evolution. The recent progress of COF/MOF-supported single-atom catalysts for photocatalytic N₂ fixation is well concluded. Future opportunities and perspectives are discussed for the further development of advanced photocatalytic N₂ fixation catalysts to produce NH₃.

Pyridines and quinolines are prevalent aza-arene motifs existing in drugs and natural products. It is of great interest to develop a more step- and atom-economy strategy for the construction of quinolines from more accessible pyridines. Herein, a visible-light-induced intermolecular cascade cyclization is developed for the coupling of halopyridies with diynes or dienes to construct tricyclic aza-arenes. Mechanistic studies indicate that the reaction processes include pyridyl radical generation, radical cascade addition, and cyclization processes. A series of fused-ring aza-arenes, such as quinoline, isoquinoline, and 5,6,7,8-tetrahydroquinoline, could be obtained via this protocol. Scale-up reaction and further transformations demonstrate the synthetic utility of this approach.