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231.
Guangcan Xu Sbastien Leloux Pinglu Zhang Jorge Meijide Surez Yongmin Zhang Etienne Derat Mickaël Mnand Olivia Bistri‐Aslanoff Sylvain Roland Tom Leyssens Olivier Riant Matthieu Sollogoub 《Angewandte Chemie (International ed. in English)》2020,59(19):7591-7597
The encapsulation of copper inside a cyclodextrin capped with an N‐heterocyclic carbene (ICyD) allowed both to catch the elusive monomeric (L)CuH and a cavity‐controlled chemoselective copper‐catalyzed hydrosilylation of α,β‐unsaturated ketones. Remarkably, (α‐ICyD)CuCl promoted the 1,2‐addition exclusively, while (β‐ICyD)CuCl produced the fully reduced product. The chemoselectivity is controlled by the size of the cavity and weak interactions between the substrate and internal C?H bonds of the cyclodextrin. 相似文献
232.
Anna V. Davies Keegan P. Fitzpatrick Rick C. Betori Karl A. Scheidt 《Angewandte Chemie (International ed. in English)》2020,59(23):9143-9148
As a key element in the construction of complex organic scaffolds, the formation of C?C bonds remains a challenge in the field of synthetic organic chemistry. Recent advancements in single‐electron chemistry have enabled new methods for the formation of various C?C bonds. Disclosed herein is the development of a novel single‐electron reduction of acyl azoliums for the formation of ketones from carboxylic acids. Facile construction of the acyl azolium in situ followed by a radical–radical coupling was made possible merging N‐heterocyclic carbene (NHC) and photoredox catalysis. The utility of this protocol in synthesis was showcased in the late‐stage functionalization of a variety of pharmaceutical compounds. Preliminary investigations using chiral NHCs demonstrate that enantioselectivity can be achieved, showcasing the advantages of this protocol over alternative methodologies. 相似文献
233.
Peng‐Ju Xia Dan Song Zhi‐Peng Ye Yuan‐Zhuo Hu Jun‐An Xiao Hao‐Yue Xiang Xiao‐Qing Chen Hua Yang 《Angewandte Chemie (International ed. in English)》2020,59(17):6706-6710
A photoinduced SET process enables the direct B?H bond activation of NHC–boranes. In contrast to common hydrogen atom transfer (HAT) strategies, this photoinduced reaction simply takes advantage of the beneficial redox potentials of NHC–boranes, thus obviating the need for extra radical initiators. The resulting NHC–boryl radical was used for the borylation of a wide range of α‐trifluoromethylalkenes and alkenes with diverse electronic and structural features, providing facile access to highly functionalized borylated molecules. Labeling and photoquenching experiments provide insight into the mechanism of this photoinduced SET pathway. 相似文献
234.
Jinhu Wei Liangliang Wu Hai‐Xu Wang Xiting Zhang Chun‐Wai Tse Cong‐Ying Zhou Jie‐Sheng Huang Chi‐Ming Che 《Angewandte Chemie (International ed. in English)》2020,59(38):16561-16571
Reliable methods for enantioselective cis‐dihydroxylation of trisubstituted alkenes are scarce. The iron(II) complex cis‐α‐[FeII(2‐Me2‐BQPN)(OTf)2], which bears a tetradentate N4 ligand (Me2‐BQPN=(R,R)‐N,N′‐dimethyl‐N,N′‐bis(2‐methylquinolin‐8‐yl)‐1,2‐diphenylethane‐1,2‐diamine), was prepared and characterized. With this complex as the catalyst, a broad range of trisubstituted electron‐deficient alkenes were efficiently oxidized to chiral cis‐diols in yields of up to 98 % and up to 99.9 % ee when using hydrogen peroxide (H2O2) as oxidant under mild conditions. Experimental studies (including 18O‐labeling, ESI‐MS, NMR, EPR, and UV/Vis analyses) and DFT calculations were performed to gain mechanistic insight, which suggested possible involvement of a chiral cis‐FeV(O)2 reaction intermediate as an active oxidant. This cis‐[FeII(chiral N4 ligand)]2+/H2O2 method could be a viable green alternative/complement to the existing OsO4‐based methods for asymmetric alkene dihydroxylation reactions. 相似文献
235.
Lin Yu Leiyang Lv Zihang Qiu Zhangpei Chen Ze Tan Yu‐Feng Liang Chao‐Jun Li 《Angewandte Chemie (International ed. in English)》2020,59(33):14009-14013
We have developed an unprecedented Pd‐catalyzed formal hydroalkylation of alkynes with hydrazones, which are generated in situ from naturally abundant aldehydes, as both alkylation reagents and hydrogen donors. The hydroalkylation proceeds with high regio‐ and stereoselectivity to form (Z)‐alkenes, which are more difficult to generate compared to (E)‐alkenes. The reaction is compatible with a wide range of functional groups, including hydroxy, ester, ketone, nitrile, boronic ester, amine, and halide groups. Furthermore, late‐stage modifications of natural products and pharmaceutical derivatives exemplify its unique chemoselectivity, regioselectivity, and synthetic applicability. Mechanistic studies indicate the possible involvement of Pd‐hydride intermediates. 相似文献
236.
237.
在微波作用下,采用高效催化剂体系,于中等极性非质子溶剂中经卤素交换氟化高效制备了系列含氟芳香醛(酮)类化合物,产品收率53·3%~92·6%,反应时间较常规加热最多可缩短80%以上。采用中等极性反应溶剂,还可突出表现出微波对反应促进的“非热效应”,从而大大拓宽了氟化反应溶剂的选择范围。 相似文献
238.
Three mesoporous molecular sieves loaded silicotungstic acids, named HSiW/SBA-15, HSiW/MCM-41, HSiW/MCM-48, were prepared and characterised by XRD, FT-IR, TEM and SEM. The catalytic performance of the prepared materials for the Baeyer-Villiger oxidation of cyclic ketones was carried out in the presence of 30%H2O2 under mild conditions. These loading materials were proved to be efficient and reusable catalysts, they all exhibited excellent catalytic performance for the Baeyer-Villiger oxidation of cyclic ketones with 30% H2O2 as oxidant. Many cyclic ketones were efficiently converted to the corresponding lactones with up to 90% conversions and high selectivities under the optimum reaction conditions. Cyclic ketones were efficiently oxidised by mesoporous materials sopported silicotungstic acid to the corresponding lactones with 30%H2O2 as oxidant. All of the catalysts showed promising recyclability in the reactions. 相似文献
239.
《Journal of Coordination Chemistry》2012,65(1-3):1-16
Kinetic and mechanistic studies of the oxidation of olefins, sulfides, and sulfoxides by [RuIV(bpy)2(O)- (PR3)](ClO4)2 (bpy = 2,2′-bipyridine; R = ethyl or phenyl) complexes have been conducted in both methylene chloride and acetonitrile. In all cases, the rate law shows a first-order dependence on both the concentration of (oxo)ruthenium(IV) species and the target substrate. In addition, product distributions of substrate oxidation exhibit a strong dependence on both the particular phosphine ligand and the solvent utilized in the experiment. On the basis of labelling experimcnts and kinetic evidence, a mechanism is proposed involving a two-electron, oxygen atom insertion into the target substrate. Notably, an (oxidized substrate)ruthenium(II) complex has been isolated and characterized for the oxidation of styrene by the (oxo)(triethylphosphine)ruthenium(IV) complex, where a cyclic voltammogram of this complex displays one quasi-reversible Ru(III)/Ru(II) couple with an E1/2 = 1.24 V vs SSCE. Kinetic analysis of styrene oxidation indicates that the formation of benzaldehyde from styrene does not occur simply by two sequential two-electron steps. In this regard, alternative mechanisms are discussed. 相似文献
240.