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排序方式: 共有926条查询结果,搜索用时 174 毫秒
921.
Nuwayo Eric Munyaneza Carlos Posada Zhen Xu Vincenzo De Altin Popiolek Griffin Paddock Charles McKee Dr. Guoliang Liu 《Angewandte Chemie (International ed. in English)》2023,62(36):e202307042
Polystyrene (PS) is one of the least recycled large-volume commodity plastics due to bulkiness of foam products and associated contaminants. PS recycling is also severely hampered by the lack of financial incentive, limited versatility, and poor selectivity of existing methods. To this end, herein we report a thermochemical recycling strategy of “degradation-upcycling” to synthesize a library of high-value aromatic chemicals from PS wastes with high versatility and selectivity. Two cascade reactions are selected to first degrade PS to benzene under mild temperatures, followed by the derivatization thereof utilizing a variety of acyl/alkyl and sulfinyl chloride additives. To demonstrate the versatility, nine ketones and sulfides of cosmetic and pharmaceutical relevance were prepared, including propiophenone, benzophenone, and diphenyl sulfide. The approach is also amenable to sophisticated upcycling reaction designs and can produce desired products stepwise. The facile and versatile approach will provide a scalable and profitable methodology for upcycling PS waste into value-added chemicals. 相似文献
922.
Luca C. Greiner Dr. Norihito Arichi Prof. Dr. Shinsuke Inuki Prof. Dr. Hiroaki Ohno 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2023,135(3):e202213653
Phenyl azides substituted by an (alkylphenyl)ethynyl group facilitate benzylic sp3(C−H) functionalization in the presence of a JohnPhosAu catalyst, resulting in indole-fused tetra- and pentacycles via divergent N- or C-cyclization. The chemoselectivity is influenced depending on the counter-anion, the electron density of the α-imino gold(I) carbene, and the alkyl groups stabilizing the benzylic carbocation originating from a 1,5-hydride shift. An isotopic labeling experiment demonstrates the involvement of an indolylgold(I) species resulting from a tautomerization that is much faster than the deauration. The formation of a benzylic sp3(C−H) functionalization leading to an indole-fused seven-membered ring is also demonstrated. 相似文献
923.
Fen Su Fengfei Lu Kun Tang Xiaokang Lv Zhongfu Luo Fengrui Che Hongyan Long Prof. Xingxing Wu Prof. Dr. Yonggui Robin Chi 《Angewandte Chemie (International ed. in English)》2023,62(45):e202310072
The direct functionalization of inert C(sp3)-H bonds to form carbon-carbon and carbon-heteroatom bonds offers vast potential for chemical synthesis and therefore receives increasing attention. At present, most successes come from strategies using metal catalysts/reagents or photo/electrochemical processes. The use of organocatalysis for this purpose remains scarce, especially when dealing with challenging C−H bonds such as those from simple alkanes. Here we disclose the first organocatalytic direct functionalization/acylation of inert C(sp3)-H bonds of completely unfunctionalized alkanes. Our approach involves N-heterocyclic carbene catalyst-mediated carbonyl radical intermediate generation and coupling with simple alkanes (through the corresponding alkyl radical intermediates generated via a hydrogen atom transfer process). Unreactive C−H bonds are widely present in fossil fuel feedstocks, commercially important organic polymers, and complex molecules such as natural products. Our present study shall inspire a new avenue for quick functionalization of these molecules under the light- and metal-free catalytic conditions. 相似文献
924.
Jian-Fei Ge Xi-Zhang Zou Xin-Ru Liu Chong-Lei Ji Xin-Yuan Zhu Prof. Dr. De-Wei Gao 《Angewandte Chemie (International ed. in English)》2023,62(32):e202307447
Asymmetric cross-couplings based on 1,2-carbon migration from B-ate complexes have been developed efficiently to access valuable organoboronates. However, enantioselective reactions triggered by 1,2-boron shift have remained to be unaddressed synthetic challenge. Here, Ir-catalyzed asymmetric allylic alkylation enabled by 1,2-boron shift was developed. In this reaction, we disclosed that excellent enantioselectivities were achieved through an interesting dynamic kinetic resolution (DKR) process of allylic carbonates at the elevated temperature. Notably, the highly valuable (bis-boryl)alkenes have enabled an array of diversifications to access versatile molecules. Extensive experimental and computational studies were conducted to elucidate the reaction mechanism of DKR process and clarify the origin of excellent enantioselectivities. 相似文献
925.
Jiaqi Zhao Ya Bai Zhenhua Li Dr. Jinjia Liu Dr. Wei Wang Pu Wang Dr. Bei Yang Dr. Run Shi Prof. Geoffrey I. N. Waterhouse Prof. Xiao-Dong Wen Prof. Qing Dai Prof. Tierui Zhang 《Angewandte Chemie (International ed. in English)》2023,62(13):e202219299
The activation of water molecules in thermal catalysis typically requires high temperatures, representing an obstacle to catalyst development for the low-temperature water-gas shift reaction (WGSR). Plasmonic photocatalysis allows activation of water at low temperatures through the generation of light-induced hot electrons. Herein, we report a layered double hydroxide-derived copper catalyst (LD-Cu) with outstanding performance for the low-temperature photo-driven WGSR. LD-Cu offered a lower activation energy for WGSR to H2 under UV/Vis irradiation (1.4 W cm−2) compared to under dark conditions. Detailed experimental studies revealed that highly dispersed Cu nanoparticles created an abundance of hot electrons during light absorption, which promoted *H2O dissociation and *H combination via a carboxyl pathway, leading to the efficient production of H2. Results demonstrate the benefits of exploiting plasmonic phenomena in the development of photo-driven low-temperature WGSR catalysts. 相似文献
926.
Xiling Wang Xiaodan Lin Yiping Jiang Xiangquan Qin Nana Ma Fuquan Yao Sheng Dong Chuanfei Liu Yingang Feng Longyi Jin Mo Xian Zhiqi Cong 《Angewandte Chemie (International ed. in English)》2023,62(13):e202217678
Applications of the peroxidase activity of cytochrome P450 enzymes in synthetic chemistry remain largely unexplored. We present herein a protein engineering strategy to increase cytochrome P450BM3 peroxidase activity for the direct nitration of aromatic compounds and terminal aryl-substituted olefins in the presence of a dual-functional small molecule (DFSM). Site-directed mutations of key active-site residues allowed the efficient regulation of steric effects to limit substrate access and, thus, a significant decrease in monooxygenation activity and increase in peroxidase activity. Nitration of several phenol and aniline compounds also yielded ortho- and para-nitration products with moderate-to-high total turnover numbers. Besides direct aromatic nitration by P450 variants using nitrite as a nitrating agent, we also demonstrated the use of the DFSM-facilitated P450 peroxidase system for the nitration of the vinyl group of styrene and its derivatives. 相似文献