Copper Nanocrystal Plane Effect on Stereoselectivity of Catalytic Deoxygenation of Aromatic Epoxides
摘要:
Previous studies have shown that crystal planes of heterogeneous catalysts could display enhanced activity, such that higher turnover or chemoselectivity could be achieved. Here we report an example where the reaction stereoselectivity was significantly affected by the catalyst crystal planes. In copper-catalyzed deoxygenation reaction of aromatic epoxides, copper cubes, wires, and plates gave the olefin products with different cis/trans selectivities, whereas homogeneous copper catalysts showed poor selectivity. Scanning tunneling microscope and density functional theory studies revealed that the different adsorption mode and higher adsorption strength of epoxide oxygen on Cu{100} plane were responsible for the observed variation of selectivity. The copper-catalyzed deoxygenation reaction provided new practical access to cis-olefins from readily available aromatic epoxides. Our work also indicated that nanocrystal catalysts may provide useful stereochemical control in organic reactions.
描述了从MCPBA现场分离Grubbs第二代催化剂的方法的开发。在这些反应中,将Grubbs催化剂溶于由1-丁基-3-甲基咪唑六氟磷酸盐和二氯甲烷的混合物(1:1 v / v)组成的溶剂中,并完全封装在由聚二甲基硅氧烷(PDMS)制成的套管中。通过交叉复分解或闭环复分解反应的一系列分子被添加到套管的内部并使其反应。在最后一步中,将溶于MeOH / H(2)O(1:1 v / v)的间氯过氧苯甲酸(MCPBA)添加到PDMS顶针的外部。有机小分子通过PDMS扩散,与MCPBA反应形成环氧化物,但Grubbs催化剂仍被封装。该结果是重要的,因为Grubbs催化剂以MCPBA与Grubbs的比例为3000:1催化分解MCPBA。该两步级联序列的产率为67%至83%。该序列背后的概念是,小的有机分子通过PDMS具有较高的通量,而大分子(例如Grubbs催化剂)和离子试剂(例如MCPBA)具有通过P
Asymmetric vanadium- and iron-catalyzed oxidations: new mild (R)-modafinil synthesis and formation of epoxides using aqueous H2O2 as a terminal oxidant
作者:Kerstin A. Stingl、Katharina M. Weiß、Svetlana B. Tsogoeva
DOI:10.1016/j.tet.2012.07.052
日期:2012.10
phenyl sulfoxide and the epoxidation of several alkenes, including terminal ones, have been realized by using new iron(III) complexes, generated in situ from primary amine-derived non-symmetrical Schiffbase ligands and aqueous H2O2 as environmentally benign oxidant. Further investigations on vanadium catalysis and the application of both catalytic systems in the synthesis of enantiomerically-enriched
A Novel Epoxidation Reaction of Olefins Using a Combination of Chloramine-M, Benzaldehyde, and Benzyltriethylammonium Chloride
作者:Dan Yang、Chi Zhang、Xue-Chao Wang
DOI:10.1021/ja993472q
日期:2000.5.1
products. Good to excellent diastereoselectivities were obtained for epoxidation of two substitutedcyclohexenes. Chloramine-T was found to give a slower reaction than Chloramine-M. cis-N-Sulfonyloxaziridine D is proposed to be the epoxidizing agent in this novel epoxidation reaction on the basis of the mechanistic studies.
A Biomimetic Iron Catalyst for the Epoxidation of Olefins with Molecular Oxygen at Room Temperature
作者:Kristin Schröder、Benoît Join、Arlin Jose Amali、Kathrin Junge、Xavi Ribas、Miquel Costas、Matthias Beller
DOI:10.1002/anie.201004623
日期:2011.2.7
It's no sacrifice: A bio‐inspired iron system, in which a β‐keto ester serves as a sacrificial cosubstrate, readily epoxidizes olefins under ambient conditions with air. Aromatic olefins are oxidized in high yields with excellent chemoselectivity. Mechanistic investigations point out substantial differences to well‐known radical‐based autoxidations.
Organic photochemistry. 77. Simultaneous capture of two distinct radical-ion intermediates generated from the EDA complexes of three-membered compounds with TCNE by photoexcitation and in the dark
作者:Tsutomu Miyashi、Masaki Kamata、Toshio Mukai
DOI:10.1021/ja00243a035
日期:1987.4
Irradiation of the electrondonor-acceptor (EDA) complexes of 2,2-diaryl-1-methylenecyclopropanes, 1,1,2,2-tetraarylcyclopropanes, 2,3-diaryloxiranes, or 2,3-diarylaziridines with tetracyanoethylene (TCNE) under aerated conditions involved oxygenation and/or the (3 + 2) cycloaddition with TCNE. The same oxygenation took place in the dark when the EDA complexes of 2,2-diaryl-1-methylenecyclopropanes
The reaction of potassiumsuperoxide with diethylchlorophosphate in the presence of 18-crown-6 ether gave at least two oxidizing agents, one of which was electrophilic and used in the oxidation of alkenes, whilst the other, nucleophilic in type, was important in the oxidation of sulphoxides.