Mononuclear Nonheme Iron(III)‐Iodosylarene and High‐Valent Iron‐Oxo Complexes in Olefin Epoxidation Reactions

High‐spin iron(III)‐iodosylarene complexes are highly reactive in the epoxidation of olefins, in which epoxides are formed as the major products with high stereospecificity and enantioselectivity. The reactivity of the iron(III)‐iodosylarene intermediates is much greater than that of the corresponding iron(IV)‐oxo complex in these reactions. The iron(III)‐iodosylarene species—not high‐valent iron(IV)‐oxo and iron(V)‐oxo species—are also shown to be the active oxidants in catalytic olefin epoxidation reactions. The present results are discussed in light of the long‐standing controversy on the one oxidant versus multiple oxidants hypothesis in oxidation reactions.     

Boehmite nano‐particles functionalized with silylpropylamine‐supported Keggin‐type heteropolyacids: Catalysts for epoxidation of alkenes

Boehmite nano‐particles with a high degree of surface hydroxyl groups were covalently functionalized by 3‐(trimethoxysilyl)‐propylamine to support H₃[PMo₁₂O₄₀], H₃[PW₁₂O₄₀], H₄[SiMo₁₂O₄₀] and H₄[SiW₁₂O₄₀] Keggin‐type heteropolyacids. After characterization of these catalysts by FT‐IR, powder X‐ray diffraction, TG/differential thermal analysis, CHN, inductively coupled plasma and transmission electron microscopy techniques, they were applied to the epoxidation of cis‐cycloocten. The progress of the reactions was investigated by gas–liquid chromatography, and the catalytic procedures were optimized for the parameters involved, such as the solvent and oxidant. The results showed that 25 mg of supported H₃[PMo₁₂O₄₀] catalyst in 1 ml C₂H₄Cl₂ with 0.5 mmol cyclooctene and 1 mmol tert‐butylhydroperoxide at reflux temperature gave 98% yield over 15 min. Recycling experiments revealed that these nanocatalysts could be repeatedly applied up to five times for a nearly complete epoxidation of cis‐cycloocten. The optimized experimental conditions were also used successfully for the epoxidation of some other alkenes, such as cyclohexene, styrene and α‐methyl styrene.     

Mononuclear Nonheme High‐Spin (S=2) versus Intermediate‐Spin (S=1) Iron(IV)–Oxo Complexes in Oxidation Reactions

Mononuclear nonheme high‐spin (S=2) iron(IV)–oxo species have been identified as the key intermediates responsible for the C?H bond activation of organic substrates in nonheme iron enzymatic reactions. Herein we report that the C?H bond activation of hydrocarbons by a synthetic mononuclear nonheme high‐spin (S=2) iron(IV)–oxo complex occurs through an oxygen non‐rebound mechanism, as previously demonstrated in the C?H bond activation by nonheme intermediate (S=1) iron(IV)–oxo complexes. We also report that C?H bond activation is preferred over C=C epoxidation in the oxidation of cyclohexene by the nonheme high‐spin (HS) and intermediate‐spin (IS) iron(IV)–oxo complexes, whereas the C=C double bond epoxidation becomes a preferred pathway in the oxidation of deuterated cyclohexene by the nonheme HS and IS iron(IV)–oxo complexes. In the epoxidation of styrene derivatives, the HS and IS iron(IV) oxo complexes are found to have similar electrophilic characters.     

Controlled epoxidation of poly(styrene‐b‐isoprene‐b‐styrene) block copolymer for the development of nanostructured epoxy thermosets

To be used as templates for nanostructured thermosets, a commercial poly(styrene‐b‐isoprene‐b‐styrene) (SIS) block copolymer (BCP) was epoxidized by three different epoxidation procedures. An exhaustive analysis of methodologies using metal catalyzed/hydrogen peroxide, dimethyldioxirane (DMDO), and meta‐chloroperbenzoic acid (m‐CPBA) was performed to obtain reactive BCPs. The DMDO approach was the best strategy to obtain highly epoxidized SIS BCP (85 mol %) without formation of side products. Careful control in BCP epoxidation by metal catalyzed/hydrogen peroxide and m‐CPBA approaches led to a maximum epoxidation degree (ED) of approximately 60 mol % without the formation of side products. The ED by metal catalyzed/hydrogen peroxide strategy could be further increased to 69 mol %, but a significant amount of crosslinking, ring opening, and polymer chain scission reactions were detected by spectroscopic and chromatographic techniques. The miscibility of epoxidized BCPs with diglycidyl ether of bisphenol‐A epoxy system before and after curing was analyzed to develop nanostructured epoxy thermosets. For ED higher than 69 mol %, BCPs were miscible, while those with lower ED presented macrophase separation. Highly epoxidized BCPs obtained by the DMDO methodology were successfully used to obtain ordered nanodomains inside the epoxy matrix, as determined by atomic force microscopy. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

胺功能化的拟薄水铝石纳米颗粒负载的Mn-V复合物：高效的烯烃环氧化催化剂

将具有高比表面积和表面高度羟基化的拟薄水铝石纳米颗粒与3-(3甲氧基硅烷)-正丙胺进行共价结合而官能团化,再用于负载硫酸氧钒和六羰基钼络合物。所得样品采用红外光谱、粉末X射线衍射、热重-差热分析、X射线光电子能谱、元素分析、电感耦合等离子体和透射电镜等技术进行了表征,并用于顺-环辛烯的环氧化反应中,优化了诸如溶剂和氧化剂等反应条件。反应过程采用气-液色谱进行监测。重复使用实验表明,该纳米催化剂可重复使用多次,并保持顺-环辛烯接近完全环氧化。所得到的优化反应条件也成功用于其它的取代烯烃的环氧化反应中。     

Dimethyldioxirane epoxidation of 3‐aryl‐1‐(3‐coumarinyl)propen‐1‐ones

Regioselective epoxidation of 3‐aryl‐1‐(3‐coumarinyl)propen‐1‐ones 1–10 by isolated dimethyldioxirane afforded the appropriate epoxides 11–20 in high (76–87%) yields.     

Efficient Noble‐Metal‐Free Catalysts Supported by Three‐Dimensional Ordered Hierarchical Porous Carbon

Development of heterogeneous catalysts has attracted increasing attention, owing to their remarkable catalytic performance and recyclability. Herein, we report well‐developed heterogeneous catalysts with a three‐dimensional ordered hierarchical structure, constructed from nickel or cobalt nanoparticles embedded in porous carbon. The obtained catalysts were fully characterized by several techniques. On account of the uniform distribution of metal nanoparticles in the porous carbon matrix and large diffusion channels that allow for effective mass transport, the catalysts exhibited superior catalytic performance for styrene epoxidation reaction. In particular, the catalysts showed good catalytic activity, high selectivity and excellent recyclability toward the styrene epoxidation. Thus, this facile approach developed allows for fabricating advanced heterogeneous catalysts with high catalytic activities for useful practical applications.     

Synthesis and characterization of novel aromatic polyimides from 4,4‐bis(p‐aminophenoxymethyl)‐ 1‐cyclohexene

A novel diamine, 4,4‐bis(p‐aminophenoxymethyl)‐1‐cyclohexene (CHEDA), was synthesized from 4,4‐bis(hydroxymethyl)‐1‐cyclohexene and p‐chloronitrobenzene by nucleophilic aromatic substitution and subsequent catalytic reduction of the intermediate dinitro compound. A series of aromatic polyimides were prepared from CHEDA and commercial dianhydrides with varying flexibility and electronic character in two‐step direct polycondensation reactions. High molecular weight polyimides with intrinsic viscosities between 0.57 and 10.2 dL/g were obtained. Most of these polyimides, excluding those from PMDA and BPDA, were soluble in polar aprotic solvents such as NMP and DMAc, and many were also soluble in CHCl₃ and THF. DSC analysis revealed glass transitions in the range of 190 to 250°C. No significant weight losses occurred below 450°C in nitrogen and 350°C in air. Bromination and epoxidation of cyclohexene double bond in CHDEA–6FDA (3e) were investigated as examples of possible polymer modifications. Qualitative epoxidation and selective bromination of the double bond were demonstated. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1189–1197, 1999     

Structural elucidation of dioxa‐cage compounds from tetrahydroisobenzofuran‐1(3H)‐one: analysis of NMR data and GIAO chemical shifts calculations

The polycyclic compounds, especially the dioxa‐cages, have attracted considerable attention in recent years. In our work, a series of 9β‐substituted 3‐oxo‐4,11‐dioxatetracyclo[5.2.1.1^5,8.0^2,6]undecane compounds were unexpectedly isolated during bromination, chlorination and epoxidation reactions of the 3‐hydroxy‐3a,4,7,7a‐tetrahydro‐4,7‐methanoisobenzofuran‐1(3H)‐one. After careful analysis of the NMR data, the chemical shifts of the isolated and the expected products were predicted by theoretical calculations using density functional theory and gauge including atomic orbitals. The best correlation between calculated and experimental data was evaluated by comparing mean absolute errors and applying DP4 probability methodology. Results from both approaches indicated a correct structural elucidation. Copyright © 2016 John Wiley & Sons, Ltd.     

Functionality,Effectiveness, and Mechanistic Evaluation of a Multicatalyst‐Promoted Reaction Sequence by Electrospray Ionization Mass Spectrometry

A multicatalytic three‐step reaction consisting of epoxidation, hydrolysis, and enantioselective monoacylation of cyclohexene was studied by using mass spectrometry (MS). The reaction sequence was carried out in a one‐pot reaction using a multicatalyst. All reaction steps were thoroughly analyzed by electrospray ionization (ESI) MS (and MS/MS), as well as high‐resolution MS for structure elucidation. These studies allow us to shed light on the individual mode of action of each catalytic moiety. Thus, we find that under the epoxidation conditions, the catalytically active N‐methyl imidazole for the terminal acylation step is partially deactivated through oxidation. This observation helps to explain the lower efficiency of the catalyst in the last step compared to the monoacylation performed separately. All reactive intermediates and products of the reaction sequence, as well as of the side‐reactions, were monitored, and we present a working mechanism of the reaction.     

Total Synthesis of (−)‐Pepluanol B: Conformational Control of the Eight‐Membered‐Ring System

The first total synthesis of the Euphorbia diterpenoid pepluanol B in both racemic and enantioenriched form involves 20 steps from a known bicyclic diol. This synthesis features an unprecedented bromo‐epoxidation to control the eight‐membered‐ring conformation. In addition, salient reactions for the construction of the tetracyclic backbone include a sterically challenging aldol reaction to establish the quaternary center, a ring closing metathesis (RCM) to forge the eight‐membered ring, and a diastereoselective cyclopropanation to assemble the embedded cyclopropane motif.     

3-次苄基6-氟-硫色满酮与3-氨基-1,2,4-三氮唑的环缩合反应研究

本文考察了溶剂、温度、反应时间和7-芳基等对3-次苄基6-氟-硫色满酮与3-氨基-1,2,4-三氮唑的环缩合反应的影响。实验结果表明在环缩合反应中同时生成了并四环的二氢嘧啶和嘧啶。而且高温时,并四环二氢嘧啶可以在没有脱氢剂的条件下直接脱氢生成嘧啶。文中合成的化合物结构经氢核磁共振谱、质谱、元素分析和X-射线单晶衍射确证。并对同时生成并四环二氢嘧啶和嘧啶的环缩合反应的机理进行了探讨。     

On‐Demand Electrochemical Epoxidation in Nano‐Electrospray Ionization Mass Spectrometry to Locate Carbon–Carbon Double Bonds

Reported here is the first on‐demand electrochemical epoxidation incorporated into the standard nano‐electrospray ionization mass spectrometry (nanoESI‐MS) workflow for double‐bond identification. The capability lies in a novel tunable electro‐epoxidation of double bonds, where onset of the reaction can be controlled by simply tuning the spray voltage. On‐demand formation of mono‐/multiple epoxides is achieved at different voltages. The electro‐epoxidized products are then fragmented by tandem MS to generate diagnostic ions, indicating the double bond position(s). The process is completed within seconds, holding great potential for high‐throughput analysis. The rapid switch‐on/off electro‐epoxidation of a single sample, the low sample consumption, the demonstrated applicability to complex lipids containing multiple double bonds, and the advantage of not requiring extra apparatus make this method attractive for use in lipid‐related biological studies.     

Ruthenium carbonyl complexes in catalytic epoxidation of olefins co‐catalyzed by isobutyl‐aldehyde

The present work shows the catalytic activity of a series of carbonyl ruthenium complexes in the epoxidation of olefins co‐catalyzed by isobutyl‐aldehyde. The complexes display catalytic activity in the epoxidation of the cyclohexene with high selectivity. Copyright © 2006 John Wiley & Sons, Ltd.     

Schiff base‐functionalized boehmite nanoparticle‐supported molybdenum and vanadium complexes: efficient catalysts for the epoxidation of alkenes

Boehmite nanoparticles, with high surface area and high degree of surface hydroxyl groups, were prepared via hydrothermal‐assisted sol–gel processing of aluminium 2‐butoxide. The produced powder was covalently functionalized with 3‐(trimethoxysilyl)propylamine, and then, in order to support vanadium oxosulfate and molybdenum hexacarbonyl complexes, all the terminal amine groups were changed to Schiff bases by refluxing with salicylaldehyde. These catalysts were applied in the epoxidation of cis‐cyclooctene and other olefins with tert‐BuOOH in CCl₄. The catalytic procedures for both catalysts were optimized for various parameters such as solvent and oxidant. Recycling experiments revealed that these heterogeneous nano‐catalysts could be repeatedly applied for the epoxidation of alkenes. Copyright © 2015 John Wiley & Sons, Ltd.     

Dimethyldioxirane as a new and effective oxidation agent for the epoxidation of α,ω‐di(isobutenyl)polyisobutylene: A convenient synthesis of α,ω‐di(2‐methyl‐3‐hydroxypropyl)‐polyisobutylene

The synthesis and characterization of α,ω‐di(2‐methyl‐2,3‐epoxypropyl)polyisobutylene are reported. The epoxidation of α,ω‐di(isobutenyl)polyisobutylene was achieved at room temperature with dimethyldioxirane, which proved to be a very effective reagent for epoxidation without the formation of byproducts. A very good agreement was found for the conversion determined by ¹H NMR and matrix‐assisted laser desorption/ionization mass spectrometry (MALDI HMS). The epoxy end groups were converted quantitatively into aldehyde termini with zinc bromide as a catalyst. The aldehyde groups were then reduced with LiAlH₄ into primary hydroxyl functions to obtain α,ω‐di(2‐methyl‐3‐hydroxylpropyl)polyisobutylene with high efficiency. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3974–3986, 2002     

4‐Methyltetrahydropyran (4‐MeTHP): Application as an Organic Reaction Solvent

4‐Methyltetrahydropyran (4‐MeTHP) is a hydrophobic cyclic ether with potential for industrial applications. We herein report, for the first time, a comprehensive study on the performance of 4‐MeTHP as an organic reaction solvent. Its broad application to organic reactions includes radical, Grignard, Wittig, organometallic, halogen‐metal exchange, reduction, oxidation, epoxidation, amidation, esterification, metathesis, and other miscellaneous organic reactions. This breadth suggests 4‐MeTHP can serve as a substitute for conventional ethers and harmful halogenated solvents. However, 4‐MeTHP was found incompatible with strong Lewis acids, and the C?O bond was readily cleaved by treatment with BBr₃. Moreover, the radical‐based degradation pathways of 4‐MeTHP, THP and 2‐MeTHF were elucidated on the basis of GC‐MS analyses. The data reported herein is anticipated to be useful for a broad range of synthetic chemists, especially industrial process chemists, when selecting the reaction solvent with green chemistry perspectives.     

Synthesis of porous supports containing N‐(p‐hydroxyphenyl)‐ or N‐(3‐4‐dihydroxybenzyl) maleimide‐anchored titanates and application as catalysts for transesterification and epoxidation reactions

N‐(p‐acetoxyphenyl)maleimide and N‐(piperonyl)maleimide were polymerized in suspension to give macroporous supports. After deprotection of the p‐acetoxyphenyl and of the piperonyl groups, resins with pendant p‐hydroxyphenyl and catechol units were obtained. These results illustrate a very easy and convenient way to synthesize phenol and catechol containing supports. Polymer‐supported transesterification and epoxidation catalysts were obtained by immobilization of Ti(OiPr)₄ and TiCl₄. These catalysts were efficient for both reactions and could be recycled several times although some titanium leaching (≤ 20%) was observed in each case. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2879–2886, 2000     

Post modification of zinc based coordination polymer to prepare Zn‐Mo‐ICP nanoparticles as efficient self‐supported catalyst for olefin epoxidation

Preparation, characterization, and catalytic properties of bimetallic coordination polymer constructed from 2‐aminoterephthalic acid as linker, zinc cations as node, and cis‐dioxo molybdenum units as catalytic active sites are reported via two pathways. Molybdenum centers were placed in N,O positions created by condensation reaction of 2‐aminoterephthalic acid with salicylaldehyde while zinc cations coordinated via carboxylic acid groups of linker to achieve infinite chains of metalo‐ligand. The obtained coordination polymer was fully characterized and its catalytic properties in the epoxidation of olefins with tert‐butyl hydroperoxide (TBHP) described. In comparison with previously reported heterogenized molybdenum catalysts, this new coordination polymer exhibited good conversion as well as high selectivity in the epoxidation of olefins. The catalyst is stable under ambient conditions and could be reused as active catalyst for at least five times.     

A green epoxidation system with poly(4‐vinylpyridine) microsphere‐supported molybdenum catalyst

The immobilization of molybdenum (Mo) compounds on poly(4‐vinylpyridine) (P4VP) microspheres for catalytic epoxidation was reported. P4VP‐supported Mo compounds were highly efficient and selective for the epoxidation of cis‐cyclooctene using hydrogen peroxide (H₂O₂) as oxygen source. When ethanol was used as solvents, outstanding catalytic activity and selectivity were observed for Mo‐containing catalysts in the epoxidation of cis‐cyclooctene. A completely green epoxidation system based on H₂O₂ and cleaner solvent has been achieved, and the heterogenized Mo catalyst can be recovered for five times without loss of its activity. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 558–562, 2010